DE102010020860B4 - Mikroferoskop - Google Patents

Abstract

Optical measuring system (10) for measuring at least one component of the deformation and / or the elongation of a measurement object (22) in at least one predetermined or predeterminable direction by means of laser speckle digital holography, comprising: a laser speckle digital holography device (12, 12- 1, 12-2, 12-3) for illuminating a scanning area of the measurement object (22), which has an out-of-plane and / or an in-plane laser speckle digital holography arrangement with at least two coherent beams, the laser Speckle digital holography device (12, 12-1, 12-2, 12-3) is constructed as a module with a housing, and a beam generating device which is designed to generate the at least two coherent beams; anda beam steering device configured to redirect the at least two coherent beams; a microscope objective (24) whose optical axis is substantially parallel to a vertical direction and which is in the optical path of the at least a portion of the light reflected by the measurement object (22) is arranged, the optical measuring system (10) being characterized in that, when viewed in the vertical direction, the laser speckle digital holography device (12, 12-1, 12-2, 12-3) below or above the microscope objective ( 24) and / or a microscope body (26) is arranged.

Description

The invention relates to optical measuring systems and optical measuring methods based on digital holography for measuring deformations and / or strains on objects, in particular on micro objects. The microobjects preferably have a cross section of less than 1 mm ² .

In the field of solid-state mechanics, laser speckle methods, in particular digital holography also called ESPI (English: Electronic Speckle Pattern Interferometry), are increasingly being used in the areas of non-destructive material testing, component optimization and deformation and strain measurement. They have a high measuring accuracy and, compared to other measuring methods, require less time and effort to prepare and carry out the deformation analysis tests.

In in-plane digital holography (ESPI) devices, the object to be measured (measurement object) is illuminated symmetrically by two coherent beams (object beams) at a predetermined angle. The interfering light of the two object beams, which is superimposed and interfering on the measurement object surface, is diffusely reflected and focused and recorded on a two-dimensional detector (usually a CCD camera).

In out-of-plane digital holography (ESPI) devices, the measurement object is illuminated only by an object beam. A reference beam coherent with the object beam is coupled into the beam path of the detector. The interfering light of the object beam and the reference beam is focused and recorded on the detector (usually a CCD camera).

Usually, an image is taken before and after the deformation of the measurement object. It is also possible to use a phase step method. For this purpose, several speckle images of the measurement object with different phase positions of one of the two illumination waves are recorded. By evaluating the recorded speckle images, the component of the deformation or elongation of the measurement object in the plane of the two illumination waves (in-plane or object plane) can be calculated using image processing.

The citations US 2009 0 128 825 A1 . Xu, L. et al .: "Studies of digital microscopic holography wth applications to microstructure testing", Applied Optics, Vol. 40, No. 28, pages 5046 to 5051 . JP 2007240465 A and JP 2007113974 A , each describe optical holographic measuring systems for measuring deformations and / or strains of a measurement object.

The object of the invention is to provide an improved optical measuring system based on digital holography (ESPI) and a corresponding method which are suitable for measuring deformations and / or strains on objects and in particular on micro-objects.

This object is achieved by an optical measuring system with the features according to claim 1, a method for measuring components of the deformation and / or elongation of objects with the features according to claim 11. Preferred embodiments of the invention are defined in the dependent claims.

• eine Laser Speckle Digital-Holographie Vorrichtung (nachfolgend Digital-Holographie oder ESPI Vorrichtung genannt) zum Beleuchten eines Abtastbereichs eines Messobjekts, welche eine out-of-plane und/oder eine in-plane Digital-Holographie Anordnung mit zumindest zwei kohärenten Strahlen aufweist,
• ein Mikroskopobjektiv dessen optische Achse im Wesentlichen parallel zu einer vertikalen Richtung ist und welches in dem optischen Pfad des zumindest einen Teils des vom Messobjekt reflektierten Lichts angeordnet ist,
• wobei, wenn gesehen in der vertikalen Richtung, die Digital-Holographie Vorrichtung unterhalb oder oberhalb des Mikroskopobjektivs und/oder eines Mikroskopgrundkörpers angeordnet ist.

According to a first aspect of the invention, an optical measuring system for measuring at least one component of the deformation and / or the elongation of a measurement object in at least one predetermined or predeterminable direction by means of digital holography, comprising:

• a laser speckle digital holography device (hereinafter referred to as digital holography or ESPI device) for illuminating a scanning area of a measurement object, which has an out-of-plane and / or an in-plane digital holography arrangement with at least two coherent beams,
• a microscope objective whose optical axis is essentially parallel to a vertical direction and which is arranged in the optical path of the at least part of the light reflected by the measurement object,
• wherein, when viewed in the vertical direction, the digital holography device is arranged below or above the microscope objective and / or a microscope body.

The vertical or vertical direction is the direction perpendicular or perpendicular to the surface of the earth or to the center of the earth. The at least two coherent beams in an in-plane digital holography (ESPI) arrangement include a first object beam and a second object beam for illuminating a scanning area of the measurement object at two different predetermined or predefinable angles. The lighting is usually symmetrical, i.e. the first and second angles are equal in magnitude, but have different signs. In an out-of-plane digital holography (ESPI) arrangement, the two coherent beams comprise a first object beam for illuminating a scanning area of the measurement object at a predetermined or predeterminable angle and a reference beam for coupling / superimposition with at least part of the light reflected by the object.

• eine Strahlerzeugungseinrichtung, welche ausgelegt ist, die zumindest zwei kohärenten Strahlen zu erzeugen, und
• eine Strahllenkungseinrichtung, welche ausgelegt ist, die zumindest zwei kohärenten Strahlen umzulenken.

Digital holography (ESPI) is constructed as a module with a housing. In particular, the digital holography (ESPI) device with an in-plane and / or out-of-plane digital holography (ESPI) arrangement comprises:

• a beam generating device, which is designed to generate the at least two coherent beams, and
• a beam steering device which is designed to deflect the at least two coherent beams.

In a digital holography (ESPI) device with an out-of-plane digital holography (ESPI) arrangement, the beam generating device is designed to generate at least one first object beam and at least one reference beam. The beam steering device is designed to deflect the first object beam onto a measurement object in such a way that a scanning area of the measurement object is illuminated by the first object beam at a predetermined or predeterminable first angle, and the reference beam in the optical path of at least part of the light of the first object beam reflected by the measurement object couple. In a digital holography (ESPI) device with an in-plane digital holography (ESPI) arrangement, the beam generating device is designed to generate at least a first and a second object beam which is coherent with the first object beam. The beam steering device is designed such that the first and the second object beam are deflected onto the measurement object in such a way that the scanning area of the measurement object is illuminated by the first object beam at a first predetermined or predeterminable angle and is illuminated by the second object beam at a second predefined or predefinable angle.

In order to implement an out-of-plane and an in-plane digital holography (ESPI) arrangement, the beam generating device can be designed or can be used to generate at least a first object beam, a second object beam and a reference beam. The beam deflection device can be designed to deflect the first object beam, the second object beam and the reference beam as described above.

By integrating the digital holography (ESPI) device with a microscope objective or with a microscope in an entire optical (microscopic) measuring system, it is possible to measure the contactless deformation and / or strain of micro objects (e.g. micro membrane, piezomotors, Y-forks, etc.) with a cross section of less than 1 mm ² . Thus, the optical measuring system and the measuring method can be used in particular in areas in which the resolution of a simple optical observation of small areas, due to the lack of magnification, is not sufficient. The application of laser speckle methods to micro-objects or micro-components with a cross-section of less than 1 mm ² has hardly been carried out so far, although the trend in industry is towards ever smaller components. As a result of miniaturization, it is becoming increasingly necessary to develop a non-contact measurement method that can provide the industry with the necessary material parameters. Since there are currently no or only very few studies on the deformation behavior of microcomponents, an understanding of the behavior of the deformations and / or the resulting strains would be of great benefit for the optimization of such components. The arrangement of the digital holography device with respect to the microscope objective or in relation to the microscope body can vary. The digital holography device is preferably arranged below the microscope objective and / or the base of the microscope. The arrangement of the digital holography device below the microscope objective (ie between the measurement object and the microscope objective) enables better illumination of the measurement object. Further advantages are a more precise in-plane examination of the measurement object and the possibility of making the lighting arms and thus the digital holography device as small or compact as possible. Furthermore, an arrangement of the digital holography device below the microscope objective is advantageous because the microscope base is located above the digital holography device and the microscope objective and thus does not impede the installation of the digital holography device and / or the measurement. However, it is also possible to arrange the digital holography device above the microscope objective and / or the microscope body.

The digital holography (ESPI) device preferably has an out-of-plane digital holography (ESPI) arrangement with at least two coherent beams, the at least two coherent beams having a first object beam for illuminating a scanning area of a measurement object under a predetermined or predeterminable one first angle; and comprise a reference beam for coupling in the optical path of at least part of the light reflected by the measurement object, and wherein a reference beam expansion device comprising at least two (arranged one after the other) diffusers is arranged in the optical path of the reference beam.

In conventional out-of-plane digital holography (ESPI) devices, different optical elements, such as mirrors, lenses, etc., are used to expand the reference beam. However, this has the disadvantage that the adjustment of such beam expansion systems is relatively complex. Furthermore, optical elements such as lenses or mirrors have an insufficient quality of the beam profile even when they are only slightly contaminated, for example by dust. According to the first aspect of the invention, a simple reference beam expansion device is proposed, which is particularly suitable for a microscopic measuring system based on the principle of digital holography. The reference beam expansion device comprises at least two diffusers, which are arranged one after the other, ie in series, in the optical path of the reference beam. Diffusers are, in particular, diffusely scattering, reflecting, refractive or diffractive optical elements. The two diffusers can each be essentially flat ground glasses, which are arranged essentially parallel to one another. The ground glasses are preferably arranged essentially perpendicular to the axis of the reference beam.

The reference beam can easily be expanded by using two diffusers (e.g. two ground glasses). The quality of the beam profile is very good and the resulting speckle size of the reference beam is relatively small. This can be particularly advantageous for use in a microscopic measuring system. The reference beam expansion device is easily adjustable and adjustable. One of the two diffusers (e.g. ground glasses) can e.g. fixed and the other movable and / or displaceable or displaceable. By moving one of the two diffusers relative to the other, the speckle size can be adjusted in a simple and efficient manner.

An intensity setting device is preferably arranged between the two diffusers, the intensity setting device preferably comprising a displaceably arranged gray wedge (double diffuser, in particular double ground glass system with integrated gray wedge). A gray wedge is usually made of black colored neutral glass. The gray wedge can be cemented with a compensating wedge to avoid blasting. The gray wedge can be arranged movably or displaceably. For example, the position of the gray wedge can be adjusted with a shifting mechanism which e.g. operated by an adjusting screw can be varied. An advantage of intensity adjustment using a gray wedge is the neutral, i.e. essentially change in intensity independent of wavelength and polarization. The gray wedge is also available in small sizes and can be easily adjusted using a screw and spring system. Advantages of a double diffuser, especially double ground glass system with an integrated gray wedge are a particularly favorable expansion with small speckles and a better dosing of the intensity of the reference beam.

The digital holography (ESPI) device preferably has an in-plane digital holography (ESPI) arrangement with at least two coherent beams, the at least two coherent beams the first object beam and a second object beam for illuminating the scanning area of the measurement object under a predetermined one or predeterminable second angle. In particular, the digital holography (ESPI) device can also be designed such that, in addition to an out-of-plane digital holography (ESPI) arrangement, an in-plane digital holography (ESPI) arrangement is also realized. The digital holography (ESPI) device can preferably be switched between the out-of-plane arrangement and the in-plane arrangement. The switching is preferably carried out by switching between the second object beam and the reference beam. The optical measuring system preferably further comprises a switch device which is designed to switch between the second object beam and the reference beam. The switch device can comprise at least one closure device and / or an optical switch.

The digital holography (ESPI) device may further comprise a phase shifting device, which is designed, when a voltage is applied, to cause a change in the optical path of at least one of the two coherent beams.

The beam path of the second object beam and the beam path of the reference beam preferably have a common section, the phase shifting device being arranged in the common section of the second object beam and the reference beam. Thus, a change in the optical path of both the reference beam and the second object beam is brought about or implemented by a phase shifting device. The number of optical components in the digital holography (ESPI) device can thus be reduced.

The phase shift device can, for example, comprise at least one mirror which can be displaced or displaced by means of a piezo actuator. The phase shifting device preferably comprises a double mirror phase shifter (90 ° double mirror phase shifter) with at least two essentially plane mirrors which are arranged such that the normals form an angle of essentially 90 ° to the plane of the respective mirror; and a piezo actuator for moving the Double mirror phase shifter. Advantages of a phase shift device with a double mirror phase shifter can be the extensive elimination of the undesired angle dependence of the adjustment path and the shift of the optical axis.

• - Aufnehmen eines Referenzbilds beim Anlegen einer Anfangspannung an die Phasenschiebungseinrichtung;
• - Schrittweise bzw. graduelles Erhöhen der Spannung an die Phasenschiebungseinrichtung und Aufnehmen eines Bilds nach jeder Erhöhung bzw. entsprechend der graduellen Erhöhung;
• - Berechnen der Spannungen V_1min und V_2min , bei welchen die Abweichung der Intensität eines jeden Bilds von der Intensität des Referenzbilds als Funktion der angelegten Spannung die ersten zwei Minima aufweist;
• - Zuordnen der Spannungsdifferenz ΔV = V_2min - V_1min einer Veränderung des optischen Wegs von Δλ (durch die Phasenschiebungseinrichtung), wobei λ die Wellenlänge der zumindest zwei kohärenten Strahlen ist.

The optical measuring system can further comprise a control device, which is designed to control and / or regulate the phase shifting device. The control device can be designed to carry out an automatic calibration process of the phase shifting device. The automatic calibration procedure includes the following steps:

• Taking a reference image when an initial voltage is applied to the phase shifter;
• - Gradually or gradually increasing the voltage to the phase shifter and taking an image after each increase or corresponding to the gradual increase;
• - Calculate the stresses V _1min and V _2min in which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima;
• - Assigning the voltage difference ΔV = V _2min - V _{1min to} a change in the optical path from Δλ (by the phase shifter) where λ is the wavelength of the at least two coherent rays.

From the calculated voltage difference .DELTA.V can be calculated automatically by evenly dividing the (for example three) voltage differences required for the individual measurements. The automatic adjustment / calibration of the phase shifting device can considerably simplify the operability of the optical measuring system. Furthermore, the random measurement deviations, such as those that occur during manual adjustment, can be considerably reduced, which leads to an increase in measurement accuracy.

Here, the intensity (total intensity) of an image is the sum of the intensities of each point of the image. The recorded image is usually a pixel image with a plurality of pixels, with a gray value being assigned to each pixel. In this case, the intensity (total intensity) of the image is calculated as the sum of the gray values of all pixels in the image.

The calibration can be carried out in in-plane as well as in out-of-plane measurement mode. The calibration described above can be used with any in-plane, out-of-plane and digital holography (ESPI) arrangements which can be switched between in-plane and out-of-plane and which use phase shifting by means of optical elements arranged on piezo actuators.
The automatic piezo calibration procedure considerably simplifies the usability and secondly reduces the random measurement errors that arise during manual adjustment.

The optical measuring system can further comprise a light source. The optical measuring system can also comprise a two-dimensional detector, which is arranged in the optical path of the at least part of the light reflected by the measurement object. The detector (for example a CCD camera) is in particular designed and arranged, in the case of an in-plane arrangement, to record an interference image of the light of the first and second object beams reflected by the measurement object (which may be focused on the detector by the microscope objective). In the case of an out-of-plane arrangement, the detector is in particular designed and arranged in such a way that it records an interference image of the light of the first object beam and the reference beam reflected by the measurement object (which may be focused on the detector by the microscope objective).

Furthermore, the optical measurement system can comprise an image evaluation device which is designed to determine or calculate the component of the deformation and / or elongation of the measurement object in at least one predetermined or predeterminable direction on the basis of the images of the scanning area of the measurement object recorded by a detector.

The image evaluation device can comprise at least one computing unit, which is or is designed or programmed using suitable image evaluation software to determine or calculate information about the component of the deformation and / or elongation of the measurement object in at least one predetermined or predeterminable direction on the basis of the interference images recorded by the detector , Conventional methods for determining the components of the deformation and / or elongation of a measurement object in at least one predetermined or predeterminable direction can be used on the basis of speckle interference images recorded using digital holography (ESPI), in particular using a phase shift method.

• - Beleuchtung eines Abtastbereichs des Messobjekts mittels der Digital-Holographie Vorrichtung;
• - Erfassen zumindest eines Interferenzbildes;
• - Berechnen zumindest einer Komponente der Verformung und/oder der Dehnung des Messobjekts in zumindest einer vorgegebenen oder vorgebbaren Richtung anhand des zumindest einen vom Detektor erfassten Interferenzbildes.

According to a second aspect of the invention, a method for measuring at least one deformation and / or expansion component of objects in at least one predetermined or predefinable direction proposed by means of an optical measuring system according to a preferred embodiment of the invention. The process includes the steps:

• - Illumination of a scanning area of the measurement object by means of the digital holography device;
• - capturing at least one interference image;
• - Calculating at least one component of the deformation and / or the elongation of the measurement object in at least one predetermined or predeterminable direction on the basis of the at least one interference image detected by the detector.

• - Aufnehmen eines Referenzbilds beim Anlegen einer Anfangspannung an die Phasenschiebungseinrichtung;
• - Schrittweise Erhöhen der Spannung an die Phasenschiebungseinrichtung und Aufnehmen eines Bilds nach jeder Erhöhung;
• - Berechnen der Spannungen V_1min und V_2min , bei welchen die Abweichung der Intensität eines jeden Bilds von der Intensität des Referenzbilds als Funktion der angelegten Spannung die ersten zwei Minima aufweist;
• - Zuordnen der Spannungsdifferenz ΔV = V_2min - V_1min eine Veränderung des optischen Wegs durch die Phasenschiebungseinrichtung von Δλ, wobei λ die Wellenlänge der zumindest zwei kohärenten Strahlen ist.

A digital holography (ESPI) device which has a phase shifting device is preferably used in the method for measuring at least one component of the deformation and / or elongation of a measurement object in at least one predetermined or predeterminable direction. The phase shifting device is designed such that when a voltage is applied, it causes a change in the optical path of the at least one of the two coherent beams. The method preferably comprises an automatic calibration of the phase shift device, comprising the steps:

• Taking a reference image when an initial voltage is applied to the phase shifter;
• Incrementally increasing the voltage to the phase shifter and taking an image after each increment;
• - Calculate the stresses V _1min and V _2min in which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima;
• - Assigning the voltage difference ΔV = V _2min - V _1min a change in the optical path through the phase shifting _device from Δλ , in which λ is the wavelength of the at least two coherent rays.

According to a third aspect of the invention, an optical measuring system for measuring at least one component of the deformation and / or elongation of a measurement object in at least one predetermined or predeterminable direction by means of digital holography (ESPI) is proposed, comprising a digital holography (ESPI) device which has an out-of-plane digital holography (ESPI) arrangement with at least two coherent beams, the at least two coherent beams having a first object beam for illuminating a scanning area of a measurement object at a predetermined or predeterminable first angle; and comprise a reference beam for coupling in the optical path of at least part of the light reflected by the measurement object, and wherein a reference beam expansion device comprising at least two (arranged one after the other) diffusers is arranged in the optical path of the reference beam.

The reference beam expansion device comprises at least two diffusers which are arranged one after the other in the optical path of the reference beam, i.e. are arranged in series. The two diffusers can each be essentially flat ground glasses, which are arranged essentially parallel to one another. The ground glasses are preferably arranged essentially perpendicular to the axis of the reference beam.

As already explained above, the use of two diffusers (e.g. two of ground glasses) allows the reference beam to be expanded in a simple manner. The quality of the beam profile is very good and the resulting speckle size of the reference beam is relatively small. The reference beam expansion device is easily adjustable and adjustable. One of the two diffusers (e.g. ground glasses) can e.g. fixed and the other movable and / or displaceable or displaceable. By moving one of the two diffusers relative to the other, the speckle size can be adjusted in a simple and efficient manner.

An intensity setting device is preferably arranged between the two diffusers, the intensity setting device preferably comprising a displaceably arranged gray wedge (double diffuser, in particular double ground glass system with integrated gray wedge).

The digital holography (ESPI) device preferably also has an in-plane digital holography (ESPI) arrangement with at least two coherent beams, the at least two coherent beams the first object beam and a second object beam for illuminating the scanning area of the measurement object under one include predetermined or predeterminable second angle. In other words, the digital holography (ESPI) device is also designed to implement an in-plane digital holography (ESPI) arrangement in addition to an out-of-plane digital holography (ESPI) arrangement.

The digital holography (ESPI) device can preferably be switched between the out-of-plane arrangement and the in-plane arrangement. The switching is preferably carried out by switching between the second object beam and the reference beam. This preferably further comprises optical measuring system a switch device which is designed to switch between the second object beam and the reference beam. The switch device can comprise at least one closure device and / or an optical switch.

The digital holography (ESPI) device may further comprise a phase shifting device, which is designed, when a voltage is applied, to cause a change in the optical path of at least one of the two coherent beams.

The beam path of the second object beam and the beam path of the reference beam preferably have a common section, the phase shifting device being arranged in the common section of the second object beam and the reference beam. Thus, a change in the optical path of both the reference beam and the second object beam is brought about or implemented by a phase shifting device. The number of optical components in the digital holography (ESPI) device can thus be reduced.

The phase shift device can, for example, comprise at least one mirror which can be displaced or displaced by means of a piezo actuator. The phase shifting device preferably comprises a double mirror phase shifter (90 ° double mirror phase shifter) with at least two essentially plane mirrors which are arranged such that the normals form an angle of essentially 90 ° to the plane of the respective mirror; and a piezo actuator for shifting the double mirror phase shifter. Advantages of a phase shift device with a double mirror phase shifter can be the extensive elimination of the undesired angle dependence of the adjustment path and the shift of the optical axis.

• - Aufnehmen eines Referenzbilds beim Anlegen einer Anfangspannung an die Phasenschiebungseinrichtung;
• - Schrittweise bzw. graduelles Erhöhen der Spannung an die Phasenschiebungseinrichtung und Aufnehmen eines Bilds nach jeder Erhöhung bzw. entsprechend der graduellen Erhöhung;
• - Berechnen der Spannungen V_1min und V_2min , bei welchen die Abweichung der Intensität eines jeden Bilds von der Intensität des Referenzbilds als Funktion der angelegten Spannung die ersten zwei Minima aufweist;
• - Zuordnen der Spannungsdifferenz ΔV = V_2min - V_1min einer Veränderung des optischen Wegs von Δλ (durch die Phasenschiebungseinrichtung), wobei λ die Wellenlänge der zumindest zwei kohärenten Strahlen ist.

The optical measuring system according to the third aspect can further comprise a control device, which is designed to control and / or regulate the phase shifting device. The control device can be designed to carry out an automatic calibration process of the phase shifting device. The automatic calibration procedure includes the following steps:

• Taking a reference image when an initial voltage is applied to the phase shifter;
• - Gradually or gradually increasing the voltage to the phase shifter and taking an image after each increase or corresponding to the gradual increase;
• - Calculate the stresses V _1min and V _2min in which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima;
• - Assigning the voltage difference ΔV = V _2min - V _{1min to} a change in the optical path from Δλ (by the phase shifter) where λ is the wavelength of the at least two coherent rays.

The calibration can be carried out in in-plane as well as in out-of-plane measurement mode. The calibration can be used with any in-plane, out-of-plane and digital holography (ESPI) arrangements which can be switched between in-plane and out-of-plane and which use phase shifting by means of optical elements arranged on piezo actuators.

The optical measurement system according to the third aspect can further comprise a microscope objective, which is arranged in the optical path of the at least part of the light reflected by the measurement object. Thus, the optical measuring system and the measuring method can be used in particular in areas in which the resolution of a simple optical observation of small areas is not sufficient due to the lack of magnification.

The optical measurement system according to the third aspect can further comprise a light source. The optical measuring system can also comprise a two-dimensional detector, which is arranged in the optical path of the at least part of the light reflected by the measurement object. Furthermore, the optical measuring system can comprise an image evaluation device which is designed to determine or calculate the component of the deformation and / or elongation of the measuring object in at least one predetermined or predeterminable direction on the basis of the images of the scanning region of the measuring object recorded by a detector.

• - Beleuchtung eines Abtastbereichs des Messobjekts mit dem ersten Objektstrahl unter einem vorgegebenen oder vorgebbaren ersten Winkel;
• - Erfassen zumindest eines Interferenzbildes des vom Messobjekt reflektierten Lichts und des Referenzstrahls mittels eines Detektors;
• - Berechnen zumindest einer Komponente der Verformung und/oder der Dehnung des Messobjekts in zumindest einer vorgegebenen oder vorgebbaren Richtung anhand des zumindest einen vom Detektor erfassten Bildes.

According to a fourth aspect of the invention, a method for measuring at least one deformation and / or strain component of objects in at least one predetermined or predeterminable direction by means of an optical measuring system according to a preferred embodiment of the invention is proposed. The process includes the steps:

• - Illumination of a scanning area of the measurement object with the first object beam at a predetermined or predeterminable first angle;
• - Detecting at least one interference image of the light reflected by the measurement object and the reference beam by means of a detector;
• - Calculating at least one component of the deformation and / or the elongation of the measurement object in at least one predetermined or predeterminable direction on the basis of the at least one image captured by the detector.

• - Aufnehmen eines Referenzbilds bei einer Anfangspannung an die Phasenschiebungseinrichtung;
• - Schrittweises bzw. graduelles Erhöhen der Spannung an die Phasenschiebungseinrichtung und Aufnehmen eines Bilds nach jeder Erhöhung bzw. in entsprechenden Intervallen;
• - Berechnen der Spannungen V_1min und V_2min , bei welchen die Abweichung der Intensität eines jeden Bilds von der Intensität des Referenzbilds als Funktion der angelegten Spannung die ersten zwei Minima aufweist;
• - Zuordnen der Spannungsdifferenz ΔV = V_2min - V_1min einer Veränderung des optischen Wegs (durch die Phasenschiebungseinrichtung) von Δλ,

wobei λ die Wellenlänge der zumindest zwei kohärenten Strahlen ist durchzuführen.Likewise, according to a fifth aspect of the invention, an optical measuring system for measuring components of the deformation and / or the stretching of objects in at least one predetermined or predeterminable direction by means of digital holography is proposed, comprising a digital holography (ESPI) device which has an out -of-plane digital holography (ESPI) arrangement and / or an in-plane digital holography (ESPI) arrangement with at least two coherent beams. The digital holography device comprises a phase shifting device which, when a voltage is applied, is designed to effect a change in the optical path of the at least one of the two coherent beams; and a control device that is configured to control and / or regulate the phase shifting device. The control device is designed to be an automatic calibration method of the phase shift device with the steps:

• Capturing a reference image at an initial voltage to the phase shifter;
• - Gradually or gradually increasing the voltage to the phase shifter and taking an image after each increase or at corresponding intervals;
• - Calculate the stresses V _1min and V _2min in which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima;
• - Assigning the voltage difference ΔV = V _2min - V _{1min to} a change in the optical path (through the phase shifting _device ) of Δλ .

where λ is the wavelength of the at least two coherent beams.

The automatic piezo calibration procedure considerably simplifies the usability and secondly reduces the random measurement errors that arise during manual adjustment.

As described above, the optical measurement system according to the fifth aspect can furthermore comprise a microscope objective which is arranged in the optical path of the at least part of the light reflected by the measurement object. Furthermore, the optical measuring system can also be a light source; and / or a two-dimensional detector which is arranged in the optical path of the at least part of the light reflected by the measurement object; and / or an image evaluation device which is designed to determine or calculate information on the at least one component of the deformation and / or the elongation of the measurement object in at least one predetermined or predeterminable direction based on the images of the scanning region of the measurement object recorded by a detector.

• - Aufnehmen eines Referenzbilds beim Anlegen einer Anfangspannung an die Phasenschiebungseinrichtung;
• - Schrittweise Erhöhen der Spannung an die Phasenschiebungseinrichtung und Aufnehmen eines Bilds nach jeder Erhöhung;
• - Berechnen der Spannungen V_1min und V_2min , bei welchen die Abweichung der Intensität eines jeden Bilds von der Intensität des Referenzbilds als Funktion der angelegten Spannung die ersten zwei Minima aufweist;
• - Zuordnen der Spannungsdifferenz ΔV = V_2min - V_1min eine Veränderung des optischen Wegs durch die Phasenschiebungseinrichtung von Δλ, wobei λ die Wellenlänge der zumindest zwei kohärenten Strahlen ist.

According to a sixth aspect of the invention, a method for measuring at least one component of the deformation and / or elongation of a measurement object in at least one predetermined or predeterminable direction by means of a digital holography (ESPI) device is proposed. The digital holography (ESPI) device has an out-of-plane and / or an in-plane digital holography (ESPI) arrangement with at least two coherent beams, the at least two coherent beams having a (first) object beam and a second Object beam or a reference beam, wherein the digital holography (ESPI) device comprises a phase shifting device, which is designed, upon application of a voltage, to cause a change in the optical path of the at least one of the two coherent beams. The method comprises an automatic calibration of the phase shift device, which comprises the steps:

• Taking a reference image when an initial voltage is applied to the phase shifter;
• Incrementally increasing the voltage to the phase shifter and taking an image after each increment;
• - Calculate the stresses V _1min and V _2min in which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima;
• - Assigning the voltage difference ΔV = V _2min - V _1min a change in the optical path through the phase shifting _device from Δλ , in which λ is the wavelength of the at least two coherent rays.

The optical measuring systems according to embodiments of the invention are in particular for measuring deformation and / or strain Particularly suitable in the micro range in the plane (in-plane) and / or perpendicular to the plane (out-of-plane) of the measurement object. The advantages of these systems are, in particular, the high stability and reliability of the measurement data, the very good contrast of the phase images with preferably microscopic resolution.

• 1 den prinzipiellen Aufbau eines optischen Messsystems für in-plane Messungen mittels Digital-Holographie (ESPI);
• 2 den prinzipiellen Aufbau eines optischen Messsystems für out-of-plane Messungen mittels Digital-Holographie (ESPI);
• 3 den prinzipiellen Aufbau eines optischen Messsystems für in-plane und out-of-plane Messungen mittels Digital-Holographie (ESPI);
• 4 eine schematische Darstellung eines optischen (mikroskopischen) Messsystems;
• 5 das Prinzip der Phasenschiebung mittels Variation des optischen Wegunterschiedes zweier Strahlen;
• 6 ein Beispiel einer Phasenschiebungseinrichtung mit einem Spiegel;
• 7 ein Beispiel einer Phasenschiebungseinrichtung mit einem Doppelspiegelphasenschieber;
• 8 ein Beispiel einer Strahlerzeugungsvorrichtung umfassend zwei Strahlteiler und eine Lichtfalle;
• 9 ein Beispiel einer Strahlaufweitung des Objektstrahls mit einem Konkavspiegel;
• 10 die Topologie des Strahlengangs in einer Digital-Holographie Vorrichtung gemäß einer ersten Ausführungsform;
• 11 die Topologie des Strahlengangs in einer Digital-Holographie Vorrichtung gemäß einer zweiten Ausführungsform;
• 12 die Topologie des Strahlengangs in einer Digital-Holographie Vorrichtung gemäß einer dritten Ausführungsform;
• 13 die Topologie des Strahlengangs in einer Digital-Holographie Vorrichtung gemäß einer vierten Ausführungsform;
• 14 die Topologie des Strahlengangs in einer Digital-Holographie Vorrichtung gemäß einer fünften Ausführungsform;
• 15 einen Ausschnitt (Befehls-Subfenster) aus einem Bildschirmfenster bzw. graphischen Benutzeroberfläche der Steuerungs- und Auswertungssoftware;
• 16 die Abhängigkeit der Intensitätsabweichung des jeweiligen Phasenbilds zum Referenzbild;
• 17 ein beispielhaftes Pixelbild

zeigen. In den Figuren werden die gleichen Bezugszeichen für gleiche oder ähnliche Elemente oder Komponenten verwendet. Einzelne Merkmale einzelner Ausführungsformen können zu weiteren Ausführungsformen kombiniert werden.Further objects, features and advantages of the present invention will become apparent from a detailed description of preferred embodiments of the present invention with reference to the drawings, in which:

• 1 the basic structure of an optical measuring system for in-plane measurements using digital holography (ESPI);
• 2 the basic structure of an optical measurement system for out-of-plane measurements using digital holography (ESPI);
• 3 the basic structure of an optical measuring system for in-plane and out-of-plane measurements using digital holography (ESPI);
• 4 a schematic representation of an optical (microscopic) measuring system;
• 5 the principle of phase shifting by varying the optical path difference between two beams;
• 6 an example of a phase shifter with a mirror;
• 7 an example of a phase shifter with a double mirror phase shifter;
• 8th an example of a beam generating device comprising two beam splitters and a light trap;
• 9 an example of a beam expansion of the object beam with a concave mirror;
• 10 the topology of the beam path in a digital holography device according to a first embodiment;
• 11 the topology of the beam path in a digital holography device according to a second embodiment;
• 12 the topology of the beam path in a digital holography device according to a third embodiment;
• 13 the topology of the beam path in a digital holography device according to a fourth embodiment;
• 14 the topology of the beam path in a digital holography device according to a fifth embodiment;
• 15 a section (command subwindow) from a screen window or graphical user interface of the control and evaluation software;
• 16 the dependence of the intensity deviation of the respective phase image on the reference image;
• 17 an exemplary pixel image

demonstrate. In the figures, the same reference symbols are used for the same or similar elements or components. Individual features of individual embodiments can be combined to form further embodiments.

1 to 3 each show the basic structure of different embodiments of an optical (microscopic) measuring system 10 for deformation and / or strain measurements using digital holography (ESPI).

The optical (microscopic) measuring system 10 includes a digital holography device 12-i (i = 1 to 3); a microscope lens 30 ; a two-dimensional detector 30 , preferably a CCD camera, with which interference images (phase images) of the scanning area of the measurement object can be recorded; as well as an optional light source 14 , The microscope lens 24 is in the optical path between the detector 30 and the measurement object 22 arranged to realize the desired enlargement. In the optical path between the detector 30 and the measurement object 22 there may also be other elements, such as the base of the microscope 26 and / or a camera adapter 28 ,

Furthermore, the optical (microscopic) measuring system 10 an image evaluation device 32 which is designed to provide information about at least one component of the deformation and / or the elongation of the measurement object in at least one predetermined or predeterminable direction on the basis of that from the detector 30 to determine recorded interference images. Method for evaluating interference images which have been recorded by means of digital holography (ESPI) (in particular using phase shift) in order to determine information about in-plane and / or out-of-plane components of the deformation and / or expansion of objects , are known per se and are not explained in detail.

The optical (microscopic) measuring system can also be used 10 a control device (not in the 1 to 3 shown), which is designed, the image acquisition by the detector 30 , preferably in real time, and / or the Phase shift, and / or to control or regulate the shutter actuation.

1 shows the basic structure of an optical measuring system 10 with an in-plane digital holography (ESPI) device 12-1 or expressed differently with a digital holography (ESPI) device which has an in-plane arrangement.

The in-plane digital holography (ESPI) device 12-1 comprises a beam generating device (not in 1 shown), which is designed to comprise at least two coherent beams, comprising a first object beam O1 and a second object beam 02 , to create. The (widened) object rays 01 and 02 are deflected in this way by means of a beam steering device, a scanning area of the object to be measured (measurement object) 22 to illuminate from different directions. Usually the measurement object 22 essentially illuminated symmetrically, the angle of incidence of the two object beams on the surface of the measurement object 22 are essentially the same in amount.

The object rays are separated by a split from the light source 14 coming beam (usually a laser beam) generated in two coherent partial beams. The two partial beams (object beams 01 and 01 ) are then by means of suitable beam expansion devices 16 . 18 expanded and by means of at least one suitable beam steering device onto the measurement object 22 directed. A phase shift device is in the optical path of one of the two object beams 20 arranged.

The light of the two object beams superimposed and / or interfering on the surface of the measurement object is reflected diffusely by the microscope objective 24 on the CCD chip of the CCD camera 30 focused and recorded. By evaluating the recorded speckle images with the image evaluation device 32 the components of the deformation and / or the elongation of the measurement object can be calculated or ascertained in the plane of the two illumination waves or in the plane of the measurement object (in-plane components).

2 shows the basic structure of an optical (microscopic) measuring system 10 with an out-of-plane digital holography (ESPI) device 12-2 or expressed differently with a digital holography (ESPI) device which has an out-of-plane arrangement.

The out-of-plane digital holography (ESPI) device 12-2 comprises a beam generating device (not in 2 shown), which is designed to have at least two coherent beams (comprising a first object beam 01 and a reference beam R ) to create. The object beam is similar to the in-plane structure 01 and the reference beam R by dividing one from the light source 14 coming beam (usually a laser beam) generated in two coherent partial beams. The two partial beams (object beam and reference beam) are then made using suitable beam expansion devices 16 and 17 widened. The expanded object beam O1 is directed onto the measurement object by means of a beam steering device. The expanded reference beam R is by means of the beam steering device in the beam path of the CCD camera 30 coupled. To adjust the intensity ratio between the object beam and the reference beam, the optical path of the reference beam can R (Reference beam path) an intensity setting device 34 to be ordered.

The phase shifter 20 can both in the optical path of the object beam O1 as well as in the optical path of the reference beam R to be ordered. However, the phase shift device is preferred 20 in the optical path of the reference beam R arranged. It has been shown that this increases the accuracy of the microscopic measuring system.

The reference beam R can be coupled into the microscopic out-of-plane (moop) measuring system at different points. The possible reference beam coupling points are in 2 as nodes R1 . R2 . R3 . R4 shown. In particular, the reference beam can be both before and after the microscope objective 24 be coupled. However, an interface is suitable, which serves as a node R3 in 2 is shown, particularly good for the coupling of the reference beam R , At this point the microscope's beam path is essentially parallel. This enables a high quality coupling with a homogeneous intensity profile. In addition, the beam path extension of the microscope is possible at this point, which is necessary due to the height of the coupling module. In addition, this location fulfills the requirement to be able to use the eyepiece-side coupling system of a conventional microscope.

The interfering light of the reference beam R and the light of the first object beam reflected by the measurement object 01 is from the detector 30 detected and on an image evaluation device 32 transmitted.

3 shows the basic structure of an optical (microscopic) measuring system with a digital holography (ESPI) device 12-3 which is between an in-plane measuring mode (or a in-plane arrangement) and an out-of-plane measurement mode (or out-of-plane arrangement) can be switched or varied. The digital holography (ESPI) device 12-3 is designed to generate at least three coherent beams, comprising a first object beam O1 , a second object beam 02 and a reference beam R , The two object rays O1 and 02 , are directed to a scanning area of the measurement object by means of a beam deflection device 22 directed. The scanning area of the measurement object 22 is from the object rays 01 and 02 from different directions, preferably illuminated essentially symmetrically. The reference beam R is in the optical path of the target 22 reflected light.

In in-plane measurement mode (or with an in-plane arrangement) - as in connection with 1 described - the two object beams O1 and 02 by means of appropriate beam expansion devices 16 and 18 and / or beam steering devices expanded and onto the measurement object 22 directed. The reference beam R by means of the switch device 36 , switched off. In out-of-plane measurement mode - as in connection with 2 described - the measurement object 22 only from one of the two object beams 01 or 02 illuminated and the reference beam R coupled in the beam path of the camera. The other object beam is switched on 36 switched off.

The switch between the in-plane measurement mode and the out-of-plane measurement mode is accordingly carried out by switching between the second object beam 02 and the reference beam R , In the out-of-plane measuring mode, in which the first object beam O1 and the reference beam R are used, the reference beam path is switched on. In the in-plane measuring mode, in which the two object beams 01 and 02 used, becomes the first object beam O1 the object beam 02 switched on.

The union of the in-plane and out-of-plane digital holography (ESPI) principles in the digital holography (ESPI) device according to this embodiment is based on the commonality that both in-plane and out-of-plane digital Holography (ESPI) measurement method use at least one object beam. At the in 3 shown three-dimensional digital holography (ESPI) device 12-3 is the first object beam O1 the shared object beam. It can also be referred to as the common optical path of the in-plane and out-of-plane digital holography (ESPI) devices.

Furthermore, for reasons related to control or control technology and / or software, it is advantageous to have a common phase shifting device 20 to be used for both measuring modes. This also saves installation space, components (for example connectors) and costs for a second phase shifting device. The phase shifter 20 can both in the optical path of the first object beam used jointly in the two measurement modes 01 as well as in the optical path of the reference beam R to be ordered. However, it has been found that the accuracy of the out-of-plane measurement is higher when there is a phase shift of the reference beam R is carried out.

In a preferred embodiment, by dividing the light source 14 coming beam initially produces two partial beams. The first sub-beam is called an object beam O1 used. The phase shift device is in the optical path of the second partial beam 20 arranged. The second sub-beam is divided into two further sub-beams, which are the second object beam O2 and the reference beam R form. Switching between the second object beam 02 and the reference beam R done by the switch device 36 , The switch device 36 comprises a first 38 and a second 40 optical shutter (shutter) and optionally at least one optical switch 42 ,

It is also advantageous if all beams (ie the object beam 01 , the object beam 02 and the reference beam R ) can be switched separately from each other. A separate piezo adjustment can thus be carried out, for example. For this reason, the optical path of the first object beam can optionally be used O1 also a second switch device 44 comprising at least one optical shutter.

The intensity ratio between the first object beam O1 and the reference beam R an intensity setting device is preferred in the reference beam path 34 arranged.

In the 1 to 3 The optical measuring systems shown can be constructed in a modular manner, the digital holography (ESPI) device being able to be designed as an independent module (hereinafter also referred to as an interferometry module or “microferoscope”). The interferometry module can be set up to match the coupling system on the eyepiece side of a microscope, preferably a stereomicroscope (eg Leica Mz16). The interferometry module can thus be mounted on a microscope (eg a stereomicroscope) without great effort. The microscope in which the interferometry module is integrated preferably has a modular structure, which is highly variable due to the possible use of different modules and their allows different combinations. In addition, this design enables the subsequent integration of a wide variety of optical components, such as beam splitters, filters or fiber couplers.

4 shows a schematic representation of an optical (microscopic) measuring system 10 , The modular digital holography (ESPI) device 12 is below the microscope 23 or the microscope optics (comprising the microscope objective). The optical axis of the microscope or microscope objective is essentially parallel to the vertical direction z. In the 4 The digital holography (ESPI) device shown has an in-plane digital holography arrangement, the measurement object being composed of two coherent object beams O1 and O2 is illuminated. Advantages of arranging the digital holography (ESPI) device below the microscope objective (or below the microscope optics) can in particular be improved illumination of the measurement object, greater accuracy of the examination or measurement, in particular with an in-plane digital holography (ESPI) arrangement , a smaller or more compact construction of the digital holography (ESPI) device (in particular the lighting arms), and a simpler integration of the digital holography (ESPI) device with a microscope.

An expansion option for simultaneous measurement of the in-plane deformations in two directions (x-x and y-y) can preferably be implemented by constructing a second, structurally identical interferometry module (possibly without reference beam coupling). In particular, the microscopic measuring system can comprise two interometry modules, which are or are arranged essentially at 90 ° to one another and 45 ° to the plateau of the column system.

Preferred embodiments of the optical measuring system 10 comprising a digital holography (ESPI) device and optionally a microscope objective are described in more detail below:

light source

The light source can be external to the digital holography (ESPI) device or to the interferometry module. The coupling of the beam generated by the light source into the digital holography (ESPI) device can be implemented, for example, by means of at least one glass fiber cable and at least one collimator. However, it is also possible for the light source to be firmly integrated in the digital holography (ESPI) device. The advantages of an internal light source are in particular that there is no need to set the coupling and the expensive and sensitive fiber optic cables can be dispensed with. The light source preferably has a laser or a laser diode. Alternatively, however, other light sources can also be used, e.g. Fluorescent tubes in combination with appropriate filters.

Beam steering device

The beam steering device comprises at least one optical element, e.g. a mirror, a beam splitter cube, etc. In particular, for beam steering or beam deflection, in addition to mirrors, beam splitter cubes can also be used as beam-guiding elements, the reflected beam usually emerging perpendicularly to the optical axis of the beam input or of the transmitted beam and thus being deflected. One or more mirrors, preferably plane mirrors, each with an adjustable mirror table, can also be used. The mirrors preferably have a coating which preferably has a very good and almost constant degree of reflection in the range of the laser wavelengths provided.

switch device

The merging of the in-plane and out-of-plane digital holography (ESPI) devices into an entire three-dimensional system requires a switchover between two beam paths. For this, e.g. optical switches (beam switches) and / or closure devices (shutter devices) are used. An optical switch is designed to deflect essentially 100% of the incident light in the set or predetermined direction. The optical switch can e.g. include at least one mirror on a servo-adjustable turntable. A closure device is designed to split the incident light into at least two partial beams, to open the closure in the direction to be set and to close the closure in the second direction. An exemplary shutter device may include a beam splitter and two shutter panels.

As already explained above, it is advantageous if all beams (ie the object beam O1 , the object beam O2 and the reference beam R ) can be switched separately from each other. The result of using an optical switch is that at least one additional shutter must be installed or an exact middle position (both beam paths closed) must be set up. In addition, the reproducibility of the absolute servo positioning angles of the servo-adjustable turntable on which the turnout mirror is arranged is not always guaranteed with conventional servo devices. However, in order to be able to measure in-plane and out-of-plane deformations during the same load on the object (ie in one step), can be switched twice during a measurement. If after switching the switch mirror is no longer in the same position as when the reference pictures were taken, the normal pictures are taken with a speckle pattern shifted to the reference pictures. This falsifies the phase images and thus the measurement.

The disadvantage of the lost luminous flux at the closed shutter (shutter) can, however, be neglected, since the light sources (especially laser sources) generally have sufficient power reserves. The locking system has therefore proven to be advantageous.

Phase shift means

The phase shift can be determined by varying the optical path difference between two partial beams (beam 1 , Beam 2 ) can be realized as in 5 shown schematically. This variation of the optical path difference can take place, for example, by moving a mirror by means of a piezoelectric actuator (piezo actuator), as in 6 shown schematically. In particular, the optical path change can be done by a 90 ° deflection mirror M1 , which is moved perpendicular to the mirror surface. However, this procedure has the disadvantage that the adjustment path is dependent on the equation 2 · cos 45 ° and there is a shift in the optical axis of the output beam by Δl · cos 45 °. For comparison, the output beam is shown in dashed lines.

A preferred alternative realization of the optical path change is therefore proposed, by means of which the undesired dependence of the adjustment path and the displacement of the optical axis can be largely eliminated. The optical path change and thus the phase shift takes place through two opposite (180 °) mirrors. One of the two mirrors can be moved by means of a piezo element or piezo actuator. This leads to a change in the optical path and thus to a phase shift. If the offset angles are very small, the influences on the beam geometry when one of the two mirrors are displaced are also small.

Another realization of the optical path change can take place by means of a 90 ° double mirror phase shifter 45 according to the retroreflector principle, as in FIG 7 shown schematically. The laser beam is over two rectangular mirrors M1 . M2 guided. These are shifted in parallel with each other. The 90 ° double mirror phase shifter essentially completely eliminates the problems described. In addition to the straight path factor ( 2Δl ) the condition is advantageously met that the beam path change takes place coaxially. Another advantage is that the phase shift ( .DELTA.l ) this phase shifting device has the same dependence on the piezo voltage as in existing shearography sensors and in the Michelson design (for "classic" piezo adjustment).

Ray generating device

The beam generating device is designed to generate at least two coherent beams. Preferably, the at least two coherent beams are generated by dividing the beam from the light source (e.g. a laser beam) into partial beams. The beam can be split, for example, using beam splitter cubes. The two object beams preferably have the same intensities. A lower intensity is usually sufficient for the reference beam.

The beam of the light source arriving in the three-dimensional digital holography (ESPI) device can be divided into three partial beams, for example with two beam splitter cubes connected in series, each of which has a splitting ratio R / T = 50/50. As a result, the beam coming from the light source with an intensity I is split into two partial beams with the same intensity I / 4 and one partial beam with an intensity I / 2. If the same division ratios are to be used in order to obtain equally high beam intensities, the intensity of a partial beam can be reduced, for example by using a filter. However, this solution has the consequence that an additional attenuator is introduced in the digital holography (ESPI) device. In the coherent optics, however, it is generally preferred to install as few attenuators as possible in the division path in order to reduce the occurrence of interfering interference effects. The causes of these interference effects can be reflections in the filter and / or scattered light occurring on the filter surface, as well as the large gradient of the strong intensity gradient over a short distance.

Furthermore, beam splitter cubes connected in series with an unequal splitter ratio can be used for beam splitting. The first beam splitter cube can e.g. have a division ratio of 67/33 and the second beam splitter cube have a division ratio of 50/50. All partial beams then have the same intensity, namely one third of the intensity of the beam originating from the light source. The system is therefore advantageously largely loss-free (except for component efficiencies). However, beam splitter cubes with a broken splitter ratio are required for this. Beam splitter cubes with broken splitter ratios are usually custom-made, which can increase the cost of the entire system.

Another way of obtaining equal division ratios is to divide the beam coming from the light source into four partial beams, each of which has a quarter of the total intensity. Since only three partial beams are required, one partial beam is derived from the digital holography (ESPI) device or, for example, absorbed in a light trap, as in 8th shown schematically. The beam splitting device accordingly comprises three beam splitter cubes BS1 . BS2 . BS3 and a light trap LF ,

The principle of operation of a light trap is that the incident light beam is reflected as often as possible in a hollow sphere. The highly absorbent surface absorbs a large part of the luminous flux with every reflection. In this way, the beam becomes weaker with every reflection, it "runs".

The advantage of this system is that the light trap can be manufactured inexpensively, e.g. with the help of a 3D printer. In particular, the light trap can be printed in matt black using a rapid prototyping process. The rough surface of this light trap increases light absorption. The disadvantage of the lost luminous flux in the light trap branch can generally be neglected, since the light sources to be used, in particular laser sources, have sufficient power reserves.

beam expansion

The object and reference beams generated by splitting a beam coming from the light source are usually expanded. This can e.g. by means of one or more lenses (lens system). The advantage of beam expansion using a lens is that the lens can be installed and exchanged relatively easily (for example, to set a different focal length). Furthermore, a single lens requires a relatively small amount of space. Disadvantages of beam expansion by means of a lens are the tendency towards non-homogeneous beam profiles and errors even with little contamination, for example due to dust. The setting of the illumination field position is also relatively complex.

A microscope objective can also be used for beam expansion. The microscope objective is relatively easy to install and easy to replace. Different focal lengths are also possible. The beam profile is better than the beam profile of a simple lens. However, a microscope objective is usually difficult to adjust because the beam has to enter exactly coaxially. Furthermore, the setting of the illumination field position is relatively complex. Furthermore, the intensity of the expanded beam is relatively low and the efficiency is relatively low.

The beam expansion can also be done by means of one or more diffusers, e.g. Ground glasses. Advantages of beam expansion using one or more diffusers (especially ground glasses) is that they can be easily installed and adjusted. The beam profile is also of good quality. The system is also easy to adjust, since it is sufficient, for example, to mount a mirror behind a fixed diffuser (e.g. a ground glass) so that it can move or adjust. Furthermore, a ground glass can simultaneously serve as a housing window, which protects the housing of the digital holography (ESPI) device from dust ingress.

With a diffuser (e.g. with a ground glass), normal size speckles can be obtained, whereas the use of a second ground glass or additional ground glasses makes it possible to reduce the speckle size. This can be particularly advantageous for use in a microscopic measuring system. One of the two diffusers (e.g. ground glasses) is preferably arranged to be movable or adjustable (e.g. in a holder). The speckle size can be adjusted to a certain extent by moving this diffuser. The second diffuser (e.g. the second ground glass) can be permanently installed, preferably at a location where it provides an inexpensive speckle size in the optical measuring system.

Furthermore, a double iris diaphragm can optionally be used to set the speckle size on the chip of the CCD camera. A small diameter aperture leads to large speckles and vice versa. The speckle size of the object image is also influenced by the aperture diaphragm of the microscope. A suitable speckle size can be specified by the reference beam expansion using two diffusers (e.g. two ground glasses). The speckle image of the object can be adapted to that of the reference beam using the aperture diaphragm of the microscope.

It is therefore advantageous, in an out-of-plane arrangement, to expand at least the reference beam with a beam expansion device which comprises two diffusers (e.g. ground glasses) arranged one after the other.

Disadvantages of a beam expansion using one or more diffusers (eg ground glasses) can be a strong beam expansion at a short distance and a limited variable degree of expansion. It is also usually necessary to place the diffuser (e.g. the ground glass) relatively close to the measurement object in order to avoid a small spot or Illuminate the scanning area accordingly bright. In this case, however, a lighter center can arise in the beam profile.

The object beam / object beams can therefore be expanded by means of other beam expansion devices, for example by using at least one concave mirror 46 , as in 9 shown schematically. The geometry of the beam expansion is determined by the laser beam diameter d, the mirror focus f and the distance from the object s. Advantages of beam expansion with a concave mirror are simple adjustment and a very good beam profile. Exchangeable concave mirrors can be used to achieve different degrees of expansion and / or illumination field diameter. The system is easily adjustable, as a mirror is mounted on an adjustable mirror table, and the lighting field position can be adjusted. Furthermore, a deflecting mirror can optionally be saved. To ensure good beam profiles for a long time, the system must be protected from dust. The concave mirror can thus be positioned behind a float glass window in the housing of the digital holography (ESPI) device, which protects the digital holography (ESPI) device from dust ingress. A disadvantage of the beam expansion by means of a concave mirror, however, is that an elliptical beam profile is generated when the input and output beams are not coaxial.

Coupling of the reference beam and intensity introduction device)

In the out-of-plane arrangement or in the out-of-plane measurement mode, the reference beam is preferably coupled in such a way that the microscope beam path is not offset. This means that the direction and position of the axis up to the camera tube can be retained. Therefore, the use of beam-displacing components, such as a beam splitter plate, is less advantageous. Beam splitter cubes are preferably used instead for coupling the reference beam into the microscope beam path. The input and output beams can thus be coaxial with one another. A beam splitter with a splitting ratio T / R = 90/10 provides a good basic ratio between the object image and the reference beam intensity on the chip of the CCD camera. The fine adjustment can be carried out with an upstream intensity setting device.

In particular, an intensity setting device can be arranged in the optical path of the reference beam in order to adjust the intensity ratio between the object beam and the reference beam. The intensity can be set, for example, with a pair of circular polarization filters. In measurement mode, however, it can be difficult to adjust the intensity of the reference beam with a pair of circular polarization filters, since the housing of the digital holography (ESPI) device usually has to be opened for this. Furthermore, depending on the direction of polarization of the coupled laser, up to four differently sized maxima occur over 360 °. The assignment of "0%" and "100%" intensity is difficult. It is also difficult to assign the change in intensity to a specific direction of rotation. Furthermore, a lot of stray light is generated in the housing by the pair of polarization filters.

In order to achieve adjustability from the outside of the housing and in particular a clear assignment of the adjustment direction to the change in intensity, a linear system, such as a gray wedge, is preferably used. The gray wedge is usually made of black colored neutral glass. To avoid the beam offset, the gray wedge can be cemented or connected with a compensation wedge. The gray wedge can be arranged movably or displaceably. For example, the position of the gray wedge can be varied with a sliding mechanism, which is actuated by an adjusting screw.

One advantage of the gray wedge is the neutral, i.e. essentially change in intensity independent of wavelength and polarization. The gray wedge is also available in small sizes and can preferably be adjusted using a screw and spring system.

The gray wedge can be arranged between the two diffusers (e.g. ground glasses). One of the ground glasses can be arranged in front of and one behind the gray wedge (double ground glass system with integrated gray wedge). The advantages of this system are a particularly favorable expansion with small speckles and a better dosage of the intensity. Another advantage is the compact design.

The ground glass in front of the beam splitter cube can be permanently installed as a camera screen. If necessary, the ground glass can be glued in front of the gray wedge at the point at which it delivers an inexpensive speckle size in this system. The second ground glass can be mounted in a holder.

Spatial filter

Furthermore, the microscopic measuring system can comprise a spatial light filter, for example a short or a long pass filter. The filter is preferably selected such that the wavelength used is in the range of the transmission maximum of the Filters lies. In order to enable measurement operation with room lighting (fluorescent tubes), a long pass filter glass (eg long pass filter glass Schott "OG590" = orange glass with edge wavelength λ _c = 590 nm) can be used, since this blocks out or absorbs a large part of the fluorescent tube light. The filter glass can be mounted in a lens ring, which ring can be screwed onto the lens if necessary.

Topology of the beam path

• - die als ein Interferometriemodul aufgebaute Digital-Holographie (ESPI) Vorrichtung kann mit dem Kupplungssystem eines Mikroskops zwischen Mikroskopgrundkörper und Kameratubus montiert werden;
• - geringe Bauhöhe, um die Strahlengangverlängerung des Mikroskops möglichst kurz zu halten;
• - Vermeidung von Strahlkreuzungen, um z.B. eine Strahlführung in einem Kanal zu ermöglichen;
• - Strahlführung in einer Ebene, um eine Erweiterung der Optik der Digital-Holographie (ESPI) Vorrichtung für eine weitere in-plane-Messrichtung in eine zweite Eben zu ermöglichen. Eine Strahlführung in einer Ebene hat insbesondere den Vorteil, dass eine separate Laserquelle zur unabhängigen Leistungsregelung der beiden in-plane-Richtungen verwendet werden kann, ohne dass eine gegenseitige Beeinflussung stattfindet;
• - Die Strahleinkopplung erfolgt vorzugsweise auf der Geräterückseite, gegebenenfalls mit Bauraum für eine Laserdiode;
• - Das Bauelementverhältnis $B=\frac{{\displaystyle \sum BaulementePfadO1}}{{\displaystyle \sum BaulementePfadO2}},$
  
  definiert als das Verhältnis zwischen der Summe der Bauelemente entlang des optischen Pfad des ersten Objektstrahls und der Summe der Bauelemente entlang des optischen Pfads des zweiten Objektstrahls, beträgt vorzugweise ungefähr 1, um die gleiche Intensität beider Objektstrahlen zu gewährleisten. Dabei werden Spiegel und Strahlteiler gleich bewertet, da deren Wirkungsgrade ähnlich sind.

The beam path in the digital holography device can have different configurations. The topology of the beam path is preferably designed according to one or more of the following aspects:

• - The digital holography (ESPI) device, constructed as an interferometry module, can be mounted with the coupling system of a microscope between the microscope base body and the camera tube;
• - Low overall height in order to keep the beam path extension of the microscope as short as possible;
• - Avoiding beam crossings, for example to enable beam guidance in a channel;
• - Beam guidance in one plane in order to enable an expansion of the optics of the digital holography (ESPI) device for a further in-plane measurement direction in a second plane. Beam guidance in one plane has the particular advantage that a separate laser source can be used for independent power control of the two in-plane directions, without mutual interference taking place;
• - The beam coupling is preferably carried out on the back of the device, if necessary with space for a laser diode;
• - The component ratio $B=\frac{{\displaystyle \Sigma BaulementePfadO1}}{{\displaystyle \Sigma BaulementePfadO2}}.$
  
  defined as the ratio between the sum of the components along the optical path of the first object beam and the sum of the components along the optical path of the second object beam, is preferably approximately 1 in order to ensure the same intensity of both object beams. The mirrors and beam splitters are rated equally because their efficiencies are similar.

10 shows the beam topology according to a first embodiment. The one from the light source 14 coming beam is through a first beam splitter cube BS1 divided into a first and a second partial beam. The first partial beam is divided into a third and a fourth partial beam by means of a second beam splitter cube BS2. The third sub-beam passes through the mirror after being deflected M7 as a second object beam from the digital holography (ESPI) device. The fourth beam is from a light trap LF absorbed.

The second beam is created using a third beam splitter cube BS3 divided into two further (fifth and sixth) partial beams. The fifth partial beam passes through the mirror after being deflected M5 and M6 as the first object beam 01 from the digital holography (ESPI) device. The sixth sub-beam emerges as a reference beam from the digital holography (ESPI) device.

In the optical path of the second partial beam between the first beam splitter cube BS1 and the third beam splitter cube BS2 is arranged a phase shift device. The phase shifter comprises a 90 ° double mirror phase shifter 45 according to the retroreflector principle with two mirrors M1 and M2 , The double mirror phase shifter can be operated using a piezo actuator PA be moved. Furthermore, the phase shift device comprises the mirror M3 and the mirror M4 , which are preferably arranged such that the optical axis of the first partial beam is not offset after passing through the double mirror phase shifter.

11 shows the radiation topology according to a second embodiment. The one from the light source 14 coming beam is through a first beam splitter cube BS1 divided into a first and a second partial beam. The first partial beam is divided into a third and a fourth partial beam by means of a second beam splitter cube BS2. The third sub-beam occurs as the first object beam O1 from the digital holography (ESPI) device. The fourth beam is from a light trap LF absorbed. The second sub-beam is generated using a third beam splitter cube BS3 divided into two further (fifth and sixth) partial beams. The fifth sub-beam occurs as the second object beam O2 from the digital holography (ESPI) device. The sixth sub-beam is through the mirror M4 and M5 deflected and emerges as a reference beam from the digital holography (ESPI) device.

In the optical path of the second partial beam between the first BS1 and the third beam splitter cube BS3 a phase shifter is arranged. The phase shifter comprises a 90 ° double mirror phase shifter 45 according to the retroreflector principle with two mirrors M1 and M2 , The double mirror phase shifter 45 can by means of a piezo actuator PA be moved or relocated. Furthermore, the phase shift device comprises a third mirror M3 ,

12 shows the beam topology according to a third embodiment. The one from the light source 14 coming beam is through a first beam splitter cube BS1 divided into a first and a second partial beam. The first partial beam is generated by means of a second beam splitter cube BS2 divided into a third and a fourth partial beam. The third beam is through a mirror M6 deflected and emerges as the first object beam from digital holography (ESPI) device. The fourth beam is from a light trap LF absorbed. The second sub-beam is generated using a third beam splitter cube BS3 divided into two further (fifth and sixth) partial beams. The fifth sub-beam occurs as the second object beam 02 from the digital holography (ESPI) device. The sixth sub-beam is through the mirror M4 and M5 deflected and occurs as a reference beam R from the digital holography (ESPI) device.

In the optical path of the second partial beam between the first BS1 and the third beam splitter cube BS2 is arranged a phase shift device. The phase shifter comprises a 90 ° double mirror phase shifter 45 according to the retroreflector principle with two mirrors M1 and M1 , The double mirror phase shifter can be operated using a piezo actuator PA be moved or relocated. Furthermore, the phase shift device comprises a further mirror M3 , The mirror M3 and the third beam splitter cube BS1 can form a unit.

13 shows the radiation topology according to a fourth embodiment. The one from the light source 14 coming beam is through a first beam splitter cube BS1 divided into a first and a second partial beam. The first partial beam is generated by means of a second beam splitter cube BS2 divided into a third and a fourth partial beam. The third sub-beam passes through the mirror after being deflected M5 as the first object beam O1 from the digital holography (ESPI) device. The fourth beam is from a light trap LF absorbed. The second sub-beam is generated using a third beam splitter cube BS3 divided into two further (fifth and sixth) partial beams. The fifth sub-beam occurs as the second object beam 02 from the digital holography (ESPI) device. The sixth sub-beam is made using two mirrors M3 and M4 deflected and occurs as a reference beam R from the digital holography (ESPI) device.

In the optical path of the second partial beam between the first beam splitter cube BS1 and the third beam splitter cube BS2 a phase shifter is arranged. The phase shifter comprises a double mirror phase shifter 45 with two mirrors M1 and M2 , The double mirror phase shifter can be operated using a piezo actuator PA be moved or relocated.

14 shows the radiation topology according to a fifth embodiment. The beam coming from the light source is through a mirror M3 deflected and then by a first beam splitter cube BS1 divided into a first and a second partial beam. The first partial beam is generated by means of a second beam splitter cube BS2 divided into a third and a fourth partial beam. The third sub-beam is through the mirror M6 and M7 deflected and occurs as the first object beam O1 from the digital holography (ESPI) device. The fourth beam is from a light trap LF absorbed. The second sub-beam is generated using a third beam splitter cube BS3 divided into two further (fifth and sixth) partial beams. The fifth sub-beam occurs as the second object beam O2 from the digital holography (ESPI) device. The sixth sub-beam is made using two mirrors M4 and M5 deflected and emerges as a reference beam from the digital holography (ESPI) device.

In the optical path of the second partial beam between the first BS1 and the third beam splitter cube BS3 a phase shifter is arranged. The phase shifter comprises a 90 ° double mirror phase shifter 45 with two mirrors M1 and M2 , The double mirror phase shifter can be shifted or shifted by means of a piezo actuator. The first beam splitter cube BS1 and the third beam splitter cube BS2 can be integrated in a beam splitter cube unit.

In all embodiments, the beam guidance is preferably in one plane. Furthermore, closures for switching the individual beams on and off can be installed. Furthermore, in all embodiments, beam expansion devices, which are each designed, preferably become the first object beam O1 , the second object beam O2 and the reference beam R expand, built or provided.

detector

A CCD camera, for example a FireWire CCD camera, can be used as a two-dimensional detector. The advantage of the FireWire CCD camera is that no frame grabbers or other additional devices are required to connect the camera to a computer. The CCD camera can be a full-frame CCD camera in which a mechanical lock prevents light from falling on the CCD sensor during the reading process. The CCD camera can also be a frame transfer CCD camera, in which the charges very quickly after exposure to a darkened area of the CCD chip be moved. The saved image can then be read out during the next exposure time, charge packet by charge packet. Furthermore, the CCD camera can be an interline transfer CCD camera, in which the charge of each pixel is transferred laterally into a covered buffer cell. This transfer takes place for all pixels at the same time. Only then are the loads moved to the readout amplifier. No mechanical lock is necessary. The exposure time can be controlled electronically, which enables very short exposure times.

The design-related smaller light-sensitive area (poorer light sensitivity) can be compensated for by small converging lenses. These lie over each pixel and focus the light, which increases the sensor's sensitivity to light again ("lens-on-chip" technology).

Bildauswertunasvorrichtuna

The image evaluation device can comprise at least one computing unit which is designed or programmed by means of suitable image evaluation software to determine information about components of the deformation and / or the elongation of the measurement object in at least one predetermined or predeterminable direction on the basis of the interference images recorded by the detector.

The electrical and / or optical noise of each image recorded by the detector can advantageously be largely removed with a phase filter. Furthermore, the area of interest of the respective phase image can be selected with a mask and the phase image can be converted or converted into a continuous curve using a demodulation routine. By entering the necessary boundary parameters (such as illumination angle, measuring distance and laser wavelength), the result is in the form of a so-called “false color image” and / or a 3D image, each with a value scale. A profile section of the 3D image can also be output in the 2D system.

The quality of the real-time recordings can be increased by integrating a "difference factor". The image captured by the detector (CCD camera) is multiplied by this factor in order to increase the contrast of the captured image.

control device

The control device can comprise at least one computing unit, which is designed or programmed by means of suitable control software in such a way as to control or regulate the image recording, the phase shift, and / or the shutter actuation. The control device is accordingly in signal connection with the camera, and / or the phase shifting device and / or the switch device. The image evaluation software and the control software can be integrated in a control and evaluation software package.

• - Take Screenshot: Hiermit kann das momentan sichtbare Bild gespeichert werden;
• - Take Reference Image: Hiermit wird ein Referenzbild für die Bildauswertung aufgenommen und gegebenenfalls live angezeigt;
• - Take Delta Reference Image: Hiermit werden z.B. vier Bilder mit unterschiedlicher Phasenverschiebung aufgenommen.
• - Calibrate Piezo: Hiermit wird eine digitale Piezokalibrierung (nachfolgend in Detail beschrieben) gestartet;
• - Difference Factor: Mit diesem Faktor wird das aufgenommene Bild multipliziert, um den Kontrast zu erhöhen;
• - Select Camera: Dieses Feld öffnet einen Dialog, in dem eine Kamera und die dazugehörige Auflösung auswählt werden können;
• - Shutter, Gain, Brightness: Dies sind Parameter der Kamera, die eingestellt werden können;
• - Connect: Hiermit wird die Verbindung zu einem Modul „Optotronik“ hergestellt;
• - Piezo Voltage: Hiermit kann die Spannung der Piezoausgänge manuell eingestellt werden (zum Beispiel zu Testzwecken);
• - Laser Power: Dient zur Einstellung der Laserleistung;
• - Mode: In diesem Feld kann eine von z.B. vier, für die Messmodi voreingestellten, Verschlussstellungskombinationen ausgewählt oder zum Einstellen der einzelnen Strahlen eine manuelle Betätigung durchführt werden. Je nach Auswahl werden die Objektstrahlen und der Referenzstrahl ein- oder ausgeschaltet. Die Optionen können z.B. sein:
  • - „In Plane“: Die Objektstrahlen 1 und 2 sind an bzw. werden eingeschaltet.
  • - „Out Of Plane“: Der Objektstrahl 1 und der Referenzstrahl sind an bzw. werden eingeschaltet.
  • - „Manual“: Die Einstellungen werden durch die unteren Auswahlfelder getroffen.
  • - „All Off“ Alle Strahlen sind ausgeschaltet.

15 shows a section (command subwindow) 50 from a screen window or a graphical user interface of the control and evaluation software, which implements a real-time mode (I-I0), a delta mode (with phase shift), a shutter actuation and a digital piezo adjustment. The command subwindow can include several subwindows or input / output fields, such as:

• - Take screenshot: This can save the currently visible image;
• - Take Reference Image: This is used to record a reference image for image evaluation and, if necessary, to display it live;
• - Take Delta Reference Image: For example, four images with different phase shifts are recorded.
• - Calibrate Piezo: This starts a digital piezo calibration (described in detail below);
• - Difference Factor: This factor is multiplied to increase the contrast;
• - Select Camera: This field opens a dialog in which a camera and the associated resolution can be selected;
• - Shutter, Gain, Brightness: These are parameters of the camera that can be adjusted;
• - Connect: This establishes the connection to an "Optotronik"module;
• - Piezo Voltage: With this the voltage of the piezo outputs can be set manually (for example for test purposes);
• - Laser Power: used to set the laser power;
• - Mode: In this field, one of, for example, four shutter position combinations preset for the measuring modes can be selected or a manual operation can be carried out to set the individual beams. Depending on the selection, the object beams and the reference beam are switched on or off. The options can be, for example:
  • - "In Plane": The object rays 1 and 2 are on or are switched on.
  • - "Out Of Plane": The object beam 1 and the reference beam are on or are switched on.
  • - "Manual": The settings are made through the lower selection fields.
  • - "All Off" All beams are switched off.

Furthermore, the microscopic measuring system can comprise an optotronic module, which e.g. comprises three sub-modules for controlling the laser diodes, for outputting piezo voltages and / or for controlling the servos used. The optotronic module can be in signal connection with the computing unit and the CCD camera.

Before a measurement is carried out, it is advantageous to carry out an adjustment / calibration of the piezo actuators used for phase shifting (piezo adjustment / piezo calibration), since a very high degree of accuracy is important for the phase shifting (sub-µm range). The required deflection or displacement of the piezo actuator depends on several factors, in particular on the optical structure, on the wavelength of the laser used and on the piezo amplifier characteristic. Furthermore, the required deflection or displacement of the piezo actuator is dependent on the characteristic curve of the piezo stack, since when voltage [V] is applied, piezos have no linear characteristic curve with respect to deflection [d]. In order to compensate for these sources of error as well as possible, it is advantageous to carry out an adjustment or calibration of the piezo actuator.

Piezo adjustment with Michelson interferometer setup

A first piezo adjustment / piezo calibration can be carried out with the help of a Michelson setup. On the one hand, this construction has the advantage that it is very similar to the final device in the beam path. On the other hand, with the help of a Michelson structure, it is very easy to change the size (width) of the strips.

Piezo adjustment directly in digital holography (ESPI) device

An additional piezo adjustment / piezo calibration directly in the end device (i.e. directly in the optical measuring system) is also advantageous to e.g. to compensate for the inaccuracies or angular errors caused by the assembly. As a result, the assembly costs can be reduced considerably, since the individual mirrors and also the piezo mirror do not have to be assembled with a close tolerance. The piezo adjustment / piezo calibration is preferably carried out repeatedly, since changing environmental conditions (temperatures, etc.), prolonged non-use or vibrations may make it necessary to carry out a new adjustment or calibration in order to reduce measurement result inaccuracies. In order to obtain the best possible measurement result, it is recommended to carry out a piezo adjustment / piezo calibration before each measurement process. An automatic, “digital” piezo adjustment / piezo calibration is preferably carried out.

Automatic piezo adjustment / piezo calibration

The piezo actuator of the phase shift unit can be calibrated / adjusted in an in-plane or an out-of-plane construction. For this purpose, a reference image is taken at an initial voltage on the piezo actuator. The initial voltage is preferably determined in such a way that the piezo actuator operates essentially in the linear range. Then the tension is increased gradually or gradually. After each increase, a phase image is taken, or during the increase, corresponding phase images are taken (preferably with a predetermined or predeterminable timing). The increase in voltage only changes the phase of one beam, but not the phase of the other beam. Adding the two beams creates an interference pattern. Since the addition of two sine waves of the same frequency again results in a sine wave of the same frequency, the intensity changes at a certain point in the interference pattern after a sine function in such a way that when the optical path is shortened by λ, the intensity also goes through exactly one period.

In other words, if no interference factors occur, the phase-shifted image is again identical to the reference image after a change in the optical path by λ. Since the intensity changes after a sine function and the reference image is constant, the intensity deviation also changes from the phase image to the reference image after a sine function. This deviation is added for all pixels of each image. Since this is carried out for all phase images during the calibration, there is a function which maps the piezo voltage to the intensity deviation from the reference image.

In this function there are minima wherever the respective phase image is most similar to the reference image. The distance between these minima corresponds to the voltage difference .DELTA.V , where the optical path is around Δλ changed (shortened or extended). The first two minima V _1min and V _2min can be determined automatically. From the voltage difference .DELTA.V = V _2min - V _1min , the (eg three) required can be divided evenly Voltage differences for the individual images can be calculated.

16 shows the dependence of the intensity deviation of the respective phase image on the reference image. The intensity deviation of the individual phase images is plotted on the Y axis. The piezo voltage V is plotted on the X axis. To determine the intensity or total intensity of each image, all gray values which are assigned to the individual pixels in the respective image are added. 17 shows an exemplary pixel image comprising nine pixels. A gray value is assigned to each pixel.

To determine the overall intensity of an image, all gray values are preferably added. The intensity or overall intensity GW of in 17 The pixel image shown is calculated as follows: $$\text{GW}=255+204+178+153+127+102+76+51+0=\mathrm{1146th}$$

The deviation of the intensity or total intensity of each image from the intensity or overall intensity of the reference image is on the Y axis of the in 17 shown graphic plotted.

As already described above, the automatic calibration of the phase shifting device on the one hand considerably simplifies the operability of the optical measuring system and, on the other hand, the random measurement deviations, such as those that occur during manual adjustment, are reduced.

An example of a microscopic measuring system is described below. The beam path in the microscopic measuring system corresponds to that in 14 shown beam path. This beam path has optical advantages on the one hand and on the other hand the arrangement in the longitudinal direction is optimal in order to be installed in a basic housing. The number of optical elements which the laser beam coming from the light source (laser) penetrates is the same for the object beam 1 and the object beam 2.

In this example, an adjustable collimator holder is used to fine-tune the beam coupling. The optical elements are arranged on or on plate pins so that the individual optical elements or assemblies can be easily adjusted, require a small installation space and are very cheap. The beam is switched by a switch device (shutter device) comprising an object beam shutter (shutter) and a reference beam shutter (shutter). The switch device is controlled via the control device. The phase shift is carried out by a 90 ° double mirror phase shifter, since no angle error can occur with this system.

The beams are split by successively connected beam splitters. All beam splitters preferably have a beam splitting ratio of 50:50. The division compensation is achieved by using a light trap manufactured using the rapid prototyping process. The object beams are widened by a concave mirror. With this mirror, the lighting position can be adjusted, particularly in the X and Y directions. Furthermore, the concave mirrors are relatively easy to replace. By using mirrors with different focal lengths, the lighting diameter can be precisely adapted to the magnification scale. In addition, this system offers the possibility of adjusting the lighting position in the X and Y directions and adjusting the lighting diameter. The reference beam is expanded with two ground glasses connected in series. The intensity setting of the reference beam is preferably carried out with a gray wedge. The position of the gray wedge can be varied with a sliding mechanism, which is operated by an adjusting screw. The phase shift takes place by means of a 90 ° double mirror phase shifter. This has the advantage that no angular errors occur.

The digital holography (ESPI) device is constructed as a one-stop interferometry module. The housing of the interferometry module is designed so that it matches the modular system of the microscope used (Leica MZ16 in the specific example). This means that the module housing of the digital holography (ESPI) device can be mounted on a microscope without essentially having to modify the microscope. Furthermore, it is possible to set up the interferometry module in such a way that it can be used with different microscopes. For this, e.g. connectors adapted to the respective microscope can be used, which can be screwed onto the basic housing.

The housing is preferably constructed as a milled part, so that the system is as rigid as possible and therefore not susceptible to vibration. All optical components are housed in the housing. It is also possible to manufacture the housing from investment casting.

To make the module as small as possible, the optical elements such as to position the mirrors very close to each other. The optical elements are therefore preferably arranged in channels of the housing, so that the rays running in the channels cannot influence one another. In order to further reduce reflections inside the housing, this area is coated with matt black textured paint.

LIST OF REFERENCE NUMBERS

10

optical measuring system

12, 12-i, i = 1-3

Digital holography (ESPI) device

14

light source

16, 18

Objekstrahlaufweitungsvorrichtung

17

Reference beam expander

20

Phase shift device

22

measurement object

23

microscope

24

microscope objective

26

Microscope body

28

Microscope Camera Adapter

30

Detector (CCD camera)

32

Image evaluation device

34

Intensity adjustment means

36, 44

switch device

38, 40

optical shutter

42

optical switch

45

Doppespiegelphasenschieber

46

concave mirror

50

Command subwindow of the control and evaluation software

01/02

first object beam

R

reference beam

BS1-BS3

beamsplitter

M1-M8

mirror

PA

piezo actuator

LF

light trap

Claims (12)

Optical measuring system (10) for measuring at least one component of the deformation and / or the elongation of a measurement object (22) in at least one predetermined or predeterminable direction by means of laser speckle digital holography, comprising: a laser speckle digital holography device (12, 12- 1, 12-2, 12-3) for illuminating a scanning area of the measurement object (22), which has an out-of-plane and / or an in-plane laser speckle digital holography arrangement with at least two coherent beams, the laser Speckle digital holography device (12, 12-1, 12-2, 12-3) is constructed as a module with a housing, and a beam generating device, which is designed to generate the at least two coherent beams; and a beam steering device configured to deflect at least two coherent beams; a microscope objective (24), the optical axis of which is essentially parallel to a vertical direction and which is arranged in the optical path of the at least part of the light reflected by the measurement object (22), the optical measurement system (10) being characterized in that when viewed in the vertical direction, the laser speckle digital holography device (12, 12-1, 12-2, 12-3) is arranged below or above the microscope objective (24) and / or a microscope base body (26). Optical measuring system (10) according to Claim 1 , wherein the laser speckle digital holography device (12, 12-2, 12-3) has a laser speckle out-of-plane laser speckle digital holography arrangement with at least two coherent beams, the at least two coherent beams having a first object beam (01) for illuminating a scanning area of the measurement object (22) at a predetermined or predeterminable first angle and a reference beam (R) for coupling into the optical path of at least part of the light reflected by the measurement object (22), and in the optical path of the reference beam a reference beam expansion device (17) comprising at least two successively arranged diffusers is arranged. Optical measuring system (10) according to Claim 2 , wherein the two diffusers are each essentially flat ground glasses, the ground glasses being arranged essentially parallel to one another. Optical measuring system (10) according to Claim 2 or 3 , an intensity setting device being arranged between the first and the second of the two diffusers, the Intensity setting device preferably comprises a slidably arranged gray wedge. Optical measuring system (10) according to one of the preceding claims, wherein the laser speckle digital holography device (12, 12-1, 12-3) has an in-plane laser speckle digital holography (ESPI) arrangement with at least two coherent beams, wherein the at least two coherent beams comprise the first object beam (O1) and a second object beam (02) for illuminating the scanning area of the measurement object at a predetermined or predeterminable second angle. Optical measuring system (10) according to one of the preceding claims, wherein the laser speckle digital holography device (12, 12-1, 12-2, 12-3) further comprises a phase shifting device (20) which is designed when a voltage is applied to cause a change in the optical path of the at least one of the two coherent beams (O1, R). Optical measuring system (10) according to Claim 6 , wherein the phase shifting device (20) comprises: a double mirror phase shifter (45) comprising two essentially plane mirrors (M1, M2) which are arranged such that the normal to the plane of the respective mirror enclose an angle of essentially 90 °, and one Piezo actuator (PA) for moving the double mirror phase shifter. Optical measuring system (10) according to Claim 6 or 7 , further comprising a control device which is designed to control and / or regulate the phase shifting device (20), wherein the control device is designed to carry out an automatic calibration method of the phase shifting device (20), comprising: taking a reference image when applying an initial voltage the phase shifter (20); - incrementally increasing the voltage to the phase shifter (20) and taking an image after each increase; Calculating the voltages V _1min and V _2min at which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima; Assigning the voltage difference ΔV = V _2min - V _{1min to} a change in the optical path of Δλ, where λ is the wavelength of the at least two coherent beams. Optical measuring system (10) according to one of the preceding claims further comprising a two-dimensional detector (30) which is arranged in the optical path of the at least part of the light reflected by the measurement object (22). Optical measuring system (10) according to one of the preceding claims further comprising an image evaluation device (32) which is designed on the basis of the images of the scanning area of the measurement object (22) recorded by a detector (30), which at least one component of the deformation and / or the To determine the elongation of the measurement object (22) in at least one predetermined or predeterminable direction. Method for measuring at least one component of the deformation and / or elongation of a measurement object in at least one predetermined or predeterminable direction by means of an optical measurement system (10) according to one of the preceding claims, comprising the steps: - Providing the optical measuring system (10) according to one of the preceding claims; - Illumination of a scanning area of the measurement object (22) by means of the laser speckle digital holography device (12, 12-1, 12-2, 12-3) of the optical measurement system (10); - capturing at least one interference image; - Calculating the at least one component of the deformation and / or the elongation of the measurement object (22) in at least one predetermined or predeterminable direction using the at least one interference image detected by the detector (30). Method for measuring at least one component according to the deformation and / or elongation of a measurement object Claim 11 , wherein the laser speckle digital holography device (12, 12-1, 12-2, 12-3) comprises a phase shifting device (20), which is designed, when a voltage is applied, to change the optical path of the at least one of the two coherent To effect rays (O1, 02, R), and wherein the method comprises an automatic calibration of the phase shifter (20) with the following steps: - taking a reference image when an initial voltage is applied to the phase shifter (20); - Gradually increasing the voltage to the phase shifter (20) and taking an image after each increase; Calculating the voltages V _1min and V _2min at which the deviation of the intensity of each image from the intensity of the reference image as a function of the applied voltage has the first two minima; and - assigning the voltage difference ΔV = V _2min - V _{1min to} a change in the optical path of Δλ, where λ is the wavelength of the at least two coherent beams.

Images