CN102252824A - Compound differential type long-focus measuring device based on Talbot effect - Google Patents

Abstract

The invention discloses a compound differential long focal length measuring device based on the Taber effect. The light from the laser source passes through the polarizer, λ/4 wave plate, microscopic objective lens and collimator, and is divided into two beams by the splitter prism, one of which enters the standard lens, the first grating and the second grating, and passes through the first frosted glass Moiré fringes are formed on the surface, and the first CCD collects the fringes and inputs them into the computer to calculate the angle α ₁ to obtain the standard lens focal length. Moiré fringes are formed on the second frosted glass, and the second CCD collects the fringes and inputs them into the computer to calculate the fringe angle α ₂ ; make a differential correction on α ₁ and _{α 2} to obtain the long focal length value to be measured, and compare the focal length of the standard lens with its known standard value The difference is then corrected to the measured long focal length value to obtain the measured long focal length lens focal length value. The invention adopts the method of twice difference to eliminate the external interference, and can realize the high-precision measurement of the long focal length lens.

Description

Compound differential long focal length measuring device based on Taber effect

technical field

The invention belongs to the field of optical testing, in particular to a compound differential long focal length measuring device based on the Taber effect.

Background technique

In the fields of optics, astronomy and military affairs, the long focal length lens is a very critical basic component, playing an increasingly important role, and the required focal length is getting larger and larger, and the aperture is also getting larger. In large systems, such as the National Ignition Facility, long focal length lenses are the key light-gathering elements. The use of long focal length lenses requires corresponding detection technology, but there are still many difficulties in high-precision detection, especially the measurement accurate to several millimeters or even hundreds of microns. At present, there are many focal length measurement technologies. For example, a spherometer can accurately measure to 2 meters, with an accuracy of one ten-thousandth. However, as the focal length increases to tens of meters to tens of meters, most of the current methods need to stretch the beam very long, which is difficult to eliminate the influence of external interference, especially air disturbance and external vibration, and the optical path itself As the focal length increases, the aberration in the center also increases the influence on the measurement of the focal point position, and it is difficult to achieve high-precision measurement. Therefore, the easy-to-implement long focal length precision measurement method and device have a very large application space.

Contents of the invention

The object of the present invention is to provide a compound differential long focal length measuring device based on the Taber effect to address the deficiencies of the prior art.

A compound differential long focal length measurement device based on the Taber effect includes a laser light source, a polarizer, a λ/4 wave plate, a microscopic objective lens, a collimating mirror, a beam splitter, a long focal length lens to be measured, a reflector, a standard lens, The first grating, the second grating, the first ground glass, the first CCD, the third grating, the fourth grating, the second ground glass and the second CCD; the light emitted by the laser light source passes through the polarizer, λ/4 wave plate, and the microscope objective lens After being combined with the collimator, it is divided into two beams by a dichroic prism, one of which is incident on the standard lens, the first grating and the second grating, forming Moiré fringes on the first frosted glass, and the first CCD collects the fringes and inputs them into the computer to calculate the angle α ₁ , to obtain the focal length of the standard lens; the other light is incident on the long focal length lens to be measured, reflected by the mirror and incident on the third grating and the fourth grating, forming Moiré fringes on the second frosted glass, and the second CCD collects the fringes Enter the computer to calculate the fringe angle α ₂ to obtain the focal length of the long focal length lens to be measured; make a difference correction to the measured long focal length value of α ₁ and α ₂ obtained above, and continue to correct the measured long focal length by the difference between the measured standard focal length and the actual standard focal length value, so as to obtain the focal length value of the long focal length lens to be measured with high precision.

The first grating, the second grating, the third grating and the fourth grating are periodical linear gratings with a uniform structure, each period is 20-100 microns, and the thickness is 0.5-3 mm. The first grating and the third grating are placed on the electrically controlled displacement stage. The second grating and the fourth grating are placed on the electrically controlled angular displacement stage.

The beneficial effects of the present invention are:

1. The present invention uses the composite differential formula to improve the measurement accuracy, and eliminates the errors caused by external disturbances such as external air disturbance, vibration, and light source instability through two differential methods, and can also accurately correct the measured value, thereby obtaining Very accurate long focal length value, the accuracy can reach 1/10,000.

2. The present invention utilizes the Taber effect and Moiré fringe technology. This diffraction measurement technology has higher precision than the existing interferometry. It does not need to elongate the optical path. It has a compact structure and high measurement accuracy, and can achieve long focal lengths High-precision measurement of the focal length of lenses and optical systems.

3. The optical path of the present invention is compact, simple and easy to realize. The computer automatically controls the movement of the grating to adjust the Taber distance and the included angle of the grating, which can realize automatic measurement and data processing.

Description of drawings

Fig. 1 is a structural schematic diagram of a composite differential long focal length measuring device based on the Taber effect;

Fig. 2 is a flow chart of the composite difference of the present invention.

Detailed ways

The working principle of the present invention: the light beam emitted by the laser light source passes through the polarizing plate and the λ/4 wave plate, enters the microscopic objective lens and the collimating lens, and forms a parallel beam, which is divided into two beams by a beam splitter, one of which is The light beam is incident on the standard lens, the first grating and the second grating, and Moiré fringes are formed on the first frosted glass behind the second grating. The first CCD collects the fringes and inputs them into the computer to calculate the angle α ₁ to obtain the focal length of the standard lens; The light is incident on the long-focus lens to be measured, reflected by the mirror and incident on the third grating and the fourth grating, forming Moiré fringes on the second frosted glass, and the second CCD collects the fringes and inputs them into the computer to calculate the fringe angle α 2 , and obtain the fringe angle α ₂ to be measured Long focal length lens focal length. The fringe angle α 1 calculated from the moiré fringes collected by the first CCD ₁₃ and the angle α ₂ obtained from the calculation of the moiré fringes collected by the second CCD 17 are subjected to the first differential operation to obtain a revised new fringe angle α ₁ , Calculate the preliminary focal length value of the long focal length lens to be measured according to _α1 ; calculate the measured value of the standard lens focal length according to the angle _α2 calculated by the moiré fringes collected by the second CCD17, and make the second value with the accurate value of the focal length of the standard lens Then, continue to correct the initial focal length value of the long focal length lens to be measured, so as to obtain the focal length value of the long focal length lens to be measured. Such compound differential processing can eliminate the influence of factors such as air disturbance, external vibration, and light source instability, and obtain The focal length value of the high-precision long focal length lens. Among them, the polarizer and the λ/4 wave plate can ensure the unidirectional transmission of the beam, and avoid reflecting stray light from entering the laser and affecting the laser output, thus affecting the measurement accuracy.

As shown in Figure 1, a compound differential long focal length measurement device based on the Taber effect includes a laser light source 1, a polarizer 2, a λ/4 wave plate 3, a microscopic objective lens 4, a collimating mirror 5, a beam splitting prism 6, Long focal length lens 7 to be measured, reflecting mirror 8, standard lens 9, first grating 10, second grating 11, first ground glass 12, first CCD 13, third grating 14, fourth grating 15, second ground glass 16 and The second CCD17; after the light emitted by the laser light source 1 passes through the polarizer 2, the λ/4 wave plate 3, the microscopic objective lens 4 and the collimating mirror 5, it is divided into two beams by the beam splitter 6, and one of the beams is incident on the standard lens 9 , the first grating 10 and the second grating 11 form moiré fringes on the first frosted glass 12, and the first CCD13 collects the fringes and inputs them into the computer to calculate the angle α ₁ to obtain the focal length of the standard lens; the other light is incident on the long focal length to be measured The lens 7 is reflected by the mirror 8 and incident on the third grating 14 and the fourth grating 15, forming Moire fringes on the second frosted glass 16, and the second CCD 17 collects the fringes and inputs them into the computer to calculate the fringe angle α ₂ to obtain the long focal length to be measured Lens focal length; the fringe angle α ₁ calculated from the moiré fringes collected by the first CCD13 and the angle α ₂ obtained from the calculation of the moiré fringes collected by the second CCD17 are used for the first differential operation to obtain a revised new fringe angle α ₁ , calculate the preliminary focal length value of the long focal length lens to be measured according to α ₁ ; calculate the measured value of the focal length of the standard lens based on the angle α ₂ calculated from the moiré fringes collected by the second CCD17, and compare this value with the accurate value of the focal length of the standard lens Perform the second differential operation, and then continue to correct the preliminary focal length value of the long focal length lens to be measured, thereby obtaining a high-precision focal length value of the long focal length lens to be measured.

The first grating 10, the second grating 11, the third grating 14 and the fourth grating 15 are periodic linear gratings with a uniform structure, the period is 20-100 microns, and the thickness is 0.5-3 mm; the first grating 10 and the third grating 14 are placed on the electronically controlled displacement stage, which can automatically control the first grating 10 and the third grating 14 to move in the direction of the optical axis; the second grating 11 and the fourth grating 15 are placed on the electrically controlled angular displacement On the stage, the rotation of the second grating 11 and the fourth grating 15 in the direction perpendicular to the optical axis can be automatically controlled.

As shown in Figure 2 is the composite difference flowchart of the composite differential long focal length measurement method and device based on Taber effect, calculates the Moiré fringe angle _α that the first CCD13 collects and the Moiré fringe angle α that the second CCD17 collects ₂ After the first difference processing, the corrected α ₁ is obtained, so as to obtain the preliminary focal length value of the long focal length lens to be measured. The first difference can eliminate the influence of factors such as air disturbance, vibration and instability of the light source, because the two CCDs collect The fringe image is obtained by the two-way light beams separated by the beam splitting prism 6, which is a common path system; the measured value of the focal length of the standard lens is calculated according to the Moiré fringe angle _α2 collected by the second CCD17, and the value is compared with the already obtained The accurate focal length value of the standard lens is known for the second differential processing, and the obtained correction amount is introduced into the preliminary focal length value of the long focal length lens to be measured, thereby obtaining an accurate and high-precision focal length value of the long focal length lens to be measured. The second time Differential processing can further eliminate errors, so as to obtain high-precision long focal length lens focal length value.

Claims (4)

1. A compound differential long focal length measuring device based on the Taber effect, characterized in that it includes a laser light source (1), a polarizer (2), a λ/4 wave plate (3), a microscope objective lens (4), a quasi- Straight mirror (5), beam splitting prism (6), long focal length lens to be measured (7), reflector (8), standard lens (9), first grating (10), second grating (11), first frosted glass (12), the first CCD (13), the third grating (14), the fourth grating (15), the second frosted glass (16) and the second CCD (17); the light emitted by the laser light source (1) passes through the polarizer After (2), λ/4 wave plate (3), microscope objective lens (4) and collimating mirror (5), it is divided into two beams by the beam splitter prism (6), one of which is incident on the standard lens (9), The first grating (10) and the second grating (11) form Moiré fringes on the first ground glass (12), and the first CCD (13) collects the fringes and inputs them into the computer to calculate the angle α ₁ to obtain the focal length of the standard lens; One path of light is incident on the long focal length lens (7) to be measured, reflected by the mirror (8) and incident on the third grating (14) and the fourth grating (15), forming Moiré fringes on the second frosted glass (16), The second CCD (17) collects fringes and inputs them into the computer to calculate the fringe angle α ₂ to obtain the focal length of the long focal length lens to be measured; to correct the long focal length value to be measured by differentially correcting the above obtained α ₁ and α ₂ , the measured standard focal length and the actual standard The focal length difference continues to correct the long focal length value to be measured, thereby obtaining the high-precision focal length value of the long focal length lens to be measured. 2. A compound differential long focal length measuring device based on the Taber effect according to claim 1, characterized in that the first grating (10), the second grating (11), the third grating (14 ) and the fourth grating (15) are periodic linear gratings with a uniform structure, the period is 20-100 microns, and the thickness is 0.5-3 mm. 3. A compound differential long focal length measurement device based on the Taber effect according to claim 1, characterized in that the first grating (10) and the third grating (14) are placed on the electronically controlled displacement stage superior. 4. A compound differential long focal length measuring device based on the Taber effect according to claim 1, characterized in that, the second grating (11) and the fourth grating (15) are placed at an electrically controlled angular displacement on stage.

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