DE202007018689U1 - Device for stabilizing the focus position in optics for high-power laser radiation for laser material processing - Google Patents

Abstract

System for the active readjustment of the focus position for optics for high-power laser radiation for laser material processing, consisting of the following components:
a. Sensor for determining the focus position,
b. Control computer which processes the sensor data and calculates correction data for the movable axis of the optics,
c. Movable axis of the optics for changing or correcting the focus position, wherein the movable axis is realized, either
i. with a guiding machine as an axis, at whose control the correction data are transmitted, or
ii. with an additional axis between guide machine and optics, which makes the correction of the focus position by shifting the entire optics, or
iii. with an integrated into the optics additional axis, by means of which a lens or a partial lens system is movably mounted in the optics and so the focus position can be moved.

Description

The The present invention relates to a system and an apparatus for Focus position stabilization for optics for high-power laser radiation for laser material processing.

optical Elements always have an, albeit very small, absorption. For beam guidance or imaging of laser radiation with very high average power this leads to a warming and thus inevitably to a temperature gradient within the optical elements. Due to the temperature dependence The refractive index of optical glasses therefore creates an additional Refractive power (thermally induced refractive power or "thermal Lens").

The thermally induced refractive power leads to a shift the focus of the laser radiation. For example, the focus of a Laser beam of several kW of power, by the illustration of the comes from an optical fiber emerging radiation, after turning on the laser power by a few tenths to some Millimeter moved towards the optics, taking a few seconds takes up to minutes until the temperature gradient and thus the Focus position has stabilized. Whether this change of focus position has an impact on the editing process or not, depends on how big the depth of field of the laser beam is what the so-called Rayleigh length a measure is.

Of the Progress in laser technology has become more and more powerful Beam sources with high beam quality out. When imaging the laser radiation of such sources, the effect becomes the thermal lens getting bigger.

Especially big and therefore disturbing is this effect in optics with high magnification, which in modern laser systems (Fiber laser, disk laser) are increasingly being used.

The The resulting problem is therefore in the change the focus position of a laser processing optics in dependence the irradiated laser power.

In order to minimize this problem, which has long been known in principle, some proposals have been made. So will in the EP 0 365 511 described a coupled by a gas flow coupling window, which can be applied in principle to lenses. In the EP 1 380 870 It is proposed to use lenses with a planar flange to improve the heat conduction. By applying these methods, the laser beam-induced focus shift can at best be reduced, but not avoided.

To solve this problem is out of the JP 0 112 2688 A It is known to detect the thermally induced refractive power change of a focusing lens by a sensor system which measures the temperature in the center of the lens by means of an infrared radiation pyrometer and the temperature at the lens edge by means of a thermo-element. The temperature difference results in the change in the refractive power of the lens. depending on the refractive power change of the focusing lens, the focus position can then be readjusted.

The the latter method is limited in use on lens materials with an absorption that leads to a significant Temperature increase leads, as the measurement of a Temperature by radiation pyrometer succeeds only to a few degrees exactly. However, the temperature increase is only in the range less degrees, as is the case with high purity quartz lenses is, this method is far too inaccurate. In addition, that must Radiation pyrometers work in a spectral range in which the lens to be measured does not transmit the light but absorbs it, otherwise no measurement is possible. For lenses made of quartz, which have a particularly broad spectral transmission range is this process so practically impossible to carry out.

Since in a laser processing machine z. For example, for cutting, which are often equipped with a CO ₂ laser, the beam guide predominantly directly, ie does not take place by means of an optical fiber, there are numerous influences in such a device, which lead to change the beam parameters: thermal induced refractive powers of the laser Auskoppelfensters, the collimator optics and the focusing optics, but also the change of the beam path length in the procedure of the guiding machine. Accordingly complicated are known devices to keep the beam parameters on the workpiece as constant as possible.

Such genus typical device is in the GB 2 354 845 A described in which various signals are generated as a function of the thermal load of Auskoppelfenster, collimator and focusing and in dependence of the optical path and used for an adjustment or adjustment of collimator and focusing.

By contrast, such measures, which are sometimes very costly, are not applicable to optical fiber-guided high-power solid-state lasers, such as the Nd: YAG laser, diode, disk laser and fiber laser, since the effects have other orders of magnitude and the refractive power change in high-purity quartz lenses, which are predominantly used here, practically not by measuring the Temperature change is determinable.

The One reason is that the share of absorbed power much lower, and on the other hand, that is not the temperature of the lens edge, and only that is measurable enough, relevant for the refractive power change, but the temperature difference between the lens center and the lens edge, or more specifically the radial one Temperature gradient of the lens.

outgoing From this prior art, it is the object of the present Invention, system and apparatus available to make, which allows the focus position of a Laser processing optics during the machining process to keep constant and the drift of the laser processing optics during of the machining process to be compensated by suitable devices.

Solved the object of the invention by the features the independent claims.

According to the invention Accordingly, a device for stabilizing the focus position in optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in Axially mounted is movable and by a servomotor is driven, provided, wherein in a storage unit of Control calibration data are stored to the optics used and during operation the controller from the data of the Data acquisition means the instantaneous, time-dependent laser beam-induced Deviation of the focus position from the nominal position by means of calibration data is calculated, and depending on the calculated deviation the focus position from the desired focus position means Calibration data a servo motor is driven so that thereby the deviation of the focus position is compensated and the corrected Focus position so that the target focus position corresponds.

In A preferred embodiment of the invention is used as a means for Data acquisition uses an optical focus position sensor, through which a signal is delivered that of the deviation of the actual Focus position is dependent on the target focus position.

at this embodiment of the invention provides the sensor directly already the data of the deviation of the actual focus position of the target position.

Farther an embodiment of the invention is provided in which by the Data Acquisition Device Information about the instantaneous laser power be transmitted to the controller and by the controller from the time-dependent laser power data, the time-dependent Focusing position is calculated and from this a correction value for adjustment the lens group is determined.

Further is provided that the dependence of the focus position determined by the current laser power time-dependent is, wherein the determined data stored as calibration data in the memory unit or calculated on the basis of the determined data calibration data and filed.

moreover is inventively provided that the means To capture data, an interface to which the Information about the instantaneous laser power from the laser source or a higher-level control becomes. Alternatively, it is provided that the means for detecting Data include an optical sensor, through which a fraction the power of the laser beam is received and by the one of the received power dependent signal is delivered, which is subsequently transmitted to the controller.

One Another object of the present invention is a device for stabilizing the focus position in optics for high-power laser radiation for laser material processing with a control, with means for Collection of data and with an optic, in which at least one Part of the optical system movably mounted in the axial direction is and is driven by a servomotor. Such Device is by means for collecting data, which is a optical sensor, either for measuring the instantaneous Intensity of the laser beam or for measuring the axial Focusing position is suitable marked.

Farther is in a device according to the invention with an optic consisting of collimator and focusing, that the collimator or the focusing is axially adjustable and is usable for correcting the focus position.

In a further embodiment is provided according to the invention, that in an existing of 4 lens groups optics, the first group has the function of a collimator, the second group a positive refractive power, the third group a negative refractive power and the fourth group has a positive refractive power, either the second or the third lens group is axially adjustable and is suitable for correcting the focus position.

According to the invention, it is further intended that the means for acquiring data include an optical sensor which receives a fraction of the power of the laser beam and one of the received power dependent signal provides.

Preferably then the optical sensor detects the intensity of the whole Beam cross section and thus provides a proportional to the power Signal.

alternative the optical sensor detects only the intensity in the center of the beam and thus provides a signal proportional to the power density, or the optical sensor has several over the beam cross section distributed active surfaces, which the intensity distribution of the beam can be detected.

Farther is inventively provided that the optical Sensor arranged behind a highly reflective deflection mirror is and detects the transmitted residual radiation, or that the optical sensor in addition to an antireflection-coated Auskoppelspiegel is arranged and detects the reflected residual radiation.

According to the invention Also provided first calibration data, which for calculation serve the deviation of the focus position and second calibration data, which serve to adjust the focus position. This data will be either determined or obtained by calculations.

Farther are method and apparatus of the present invention for High-power solid-state lasers, in particular fiber, disk and diode lasers and Nd: YAG lasers with powers above 500 W, preferably provided above 1000 W.

According to the invention, the following components are required:
At least a part of the optical system which serves to image the laser radiation is movably mounted in the direction of the optical axis by means of a linear guide. This part of the optical system may be: a single lens of the imaging system, or a group of lenses, e.g. The collimating lens system or the focusing lens system, or the entire lens system itself.

The movable subsystem is driven by a servomotor. For the control of the servomotor, a control is needed the one arithmetic unit, a storage unit and a data acquisition unit or data interface. Via the data interface the controller gets information about the current one Laser power. This information may be from the laser source, from the higher-level control or by a sensor unit to be delivered. The arithmetic unit of the controller processes the time-dependent information about the laser power and calculates a time-dependent correction value. With this correction value, the servomotor is controlled. For the Calculating the correction value, the controller needs the behavior predict the imaging optics, the characteristic of optics must therefore be known to the controller. This characteristic becomes unique recorded and stored in the memory unit.

The Focus position is actively readjusted according to the invention. There are a number of possibilities.

• 1) Sensor zur Ermittlung der Fokusposition.
• 2) Steuerrechner, der die Sensordaten verarbeitet und daraus Korrekturdaten für die verfahrbare Achse der Optik berechnet.
• 3) Verfahrbare Achse der Optik zur Änderung bzw. Korrektur der Fokusposition. Diese Achse kann auf unterschiedliche Weise realisiert werden: a. Als Achse wird die Führungsmaschine (z. B. Roboter oder Portal) verwendet, an der die Optik befestigt ist. In diesem Fall sollten die Korrekturdaten an die Steuerung der Führungsmaschine übergeben werden. b. Zwischen Führungsmaschine und Optik wird eine zusätzliche Achse eingebaut, die die Korrektur der Fokusposition durch Verschieben der ganzen Optik vornimmt. c. In der Optik ist eine Linse oder ein Teil-Linsensystem mittels einer Zusatzachse beweglich gelagert, wodurch die Fokusposition verschoben werden kann. Die Zusatzachse ist also in die Optik integriert und damit die zusätzlich bewegten Massen besonders gering.

A first group of possible embodiments includes the following system components:

• 1) Sensor for determining the focus position.
• 2) control computer, which processes the sensor data and calculates correction data for the movable axis of the optics.
• 3) Movable axis of the optics for changing or correcting the focus position. This axis can be realized in different ways: a. The axis used is the guide machine (eg robot or portal) to which the optics are attached. In this case, the correction data should be transferred to the control of the leading machine. b. Between guide machine and optics, an additional axis is installed, which makes the correction of the focus position by moving the entire optics. c. In the optics, a lens or a partial lens system is movably mounted by means of an additional axis, whereby the focus position can be shifted. The additional axis is thus integrated into the optics and thus the additional moving masses are particularly low.

• 1) Mittel zum Erfassen der momentanen Laserleistung. Diese Mittel können sein: a. Eine Datenschnittstelle, welche Daten über die aktuelle Laserleistung von der übergeordneten Steuerung empfängt. b. Ein in der Optik angebrachter Sensor, der die Laserleistung misst. Z. B. kann das eine Photodiode sein, die einen minimalen, aber konstanten Bruchteil der Laserstrahlung empfängt.
• 2) Steuerrechner, der die Laserleistungsdaten verarbeitet, die zeitliche Änderung der Fokusposition berechnet und daraus Korrekturdaten für die verfahrbare Achse der Optik bestimmt.
• 3) Verfahrbare Achse der Optik zur Änderung bzw. Korrektur der Fokusposition. Diese Achse kann auf unterschiedliche Weise realisiert werden: a. Als Achse wird die Führungsmaschine (z. B. Roboter oder Portal) verwendet, an der die Optik befestigt ist. In diesem Fall müssen die Korrekturdaten an die Steuerung der Führungsmaschine übergeben werden. b. Zwischen Führungsmaschine und Optik wird eine zusätzliche Achse eingebaut, die die Korrektur der Fokusposition durch Verschieben der ganzen Optik vornimmt. c. In der Optik ist eine Linse oder ein Teil-Linsensystem mittels einer Zusatzachse beweglich gelagert, wodurch die Fokusposition verschoben werden kann. Die Zusatzachse ist also in die Optik integriert und damit die zusätzlich bewegten Massen besonders gering.

A second group of possible embodiments includes the following system components:

• 1) means for detecting the instantaneous laser power. These means may be: a. A data interface that receives data about the current laser power from the higher-level controller. b. An optically mounted sensor that measures laser power. For example, this may be a photodiode that receives a minimum but constant fraction of the laser radiation.
• 2) control computer, which processes the laser power data, calculates the time change of the focus position and determines therefrom correction data for the movable axis of the optics.
• 3) Movable axis of the optics for changing or correcting the focus position. This axis can be realized in different ways: a. The axis used is the guide machine (eg robot or portal) to which the optics are attached. In this case, the correction must be data are passed to the control of the guiding machine. b. Between guide machine and optics, an additional axis is installed, which makes the correction of the focus position by moving the entire optics. c. In the optics, a lens or a partial lens system is movably mounted by means of an additional axis, whereby the focus position can be shifted. The additional axis is thus integrated into the optics and thus the additional moving masses are particularly low.

Further advantageous features of the invention are in the subclaims described. The invention will be more apparent from the figures described; it shows:

1 A schematic representation of the invention in the embodiment with adjustable collimator and the internal detection of the laser power by decoupling a fraction of the beam and the use of a detector for measuring the total beam intensity.

2 A schematic representation of the invention in the adjustable focus, angled beam guide embodiment and the internal laser power measurement by measuring a fraction of the beam behind the highly reflective deflection mirror and using a multiple active area detector to measure the beam intensity distribution.

3 A schematic representation of the invention in the embodiment with adjustable lens group and the internal detection of the laser power by decoupling a fraction of the beam and the use of a detector for measuring the beam intensity in the beam center.

4 A schematic representation of the invention in the embodiment with adjustable focus and the detection of the focus position by using an autofocus sensor.

Preferred is the combination of the following components:
An optically integrated sensor 41 for measuring the laser power, a computing unit 40 for calculating the focus shift and the required correction, and an optically integrated additional axis in the form of a lens or a partial lens system ( 21 . 22 or 24 ), which with a linear guide ( 31 . 32 ) is movably mounted and driven in the beam axis ( 30 ). Such a device operates autonomously, since neither data from external components are needed and no data must be transmitted to other controllers. The integration of such a laser processing optics, which automatically corrects their focus position, in existing laser processing systems is particularly simple.

The sensor integrated into the optics 41 For measuring the laser power is preferably a photodiode, which receives a very small constant fraction of the laser beam. For this purpose, in the optical path of the optics is an antireflective coated or non-coated plane-parallel plate 26 arranged at an angle to the optical axis. In spite of the antireflection coating, a fraction of the radiation is reflected to the side (typically a few parts per thousand), which is then reflected by the likewise laterally arranged photodiode 41 falls and so generates a signal proportional to the laser power. As an alternative to the use of an anti-reflective flat plate, the laser beam can pass through a highly reflective coated plane plate in the optical path of the optical system 27 be deflected, with the photodiode 41 then in the direction of the beam behind the plane plate and receives the transmitted residual radiation (also typically a few parts per thousand).

Furthermore, it is provided to equip the integrated into the optics additional axis with a larger adjustment. The additional axis then serves not only for the laser power-dependent correction of the focus position, but in addition to the targeted adjustment of the focus position 15 in the direction of the beam axis. Thus, various tasks can be fulfilled, for. As the correction of the focus position for workpiece tolerances, or for setting a desired defocusing, which may be useful to increase the seam quality at the beginning and end of a seam.

For this purpose, the optic is preferably constructed of a total of four groups, as in 3 shown. The first group 21 (in the beam direction) is a group with positive refractive power, consisting of 2 to 4 lenses (preferably 2), which has the function of a collimator, after which the beam 12 that is, collimated, ie, approximately parallel. The second group 22 also has a positive refractive power and consists of 1 or 2 lenses (preferably 1 lens). Due to the positive refractive power of the second group, the beam now converges. It closes a third group 23 with negative refractive power, consisting of 1 or 2 lenses, after which the beam now diverges, that is widened. Finally, the fourth group follows 24 with a total of positive refractive power, consisting of 1 to 4 lenses, which finally focuses the beam. For adjusting the focus position 15 is either the second group 22 or the third group 23 movably mounted, preferably the second group 22 , The resulting benefits are: the collimator (group 1) 21 can be easily exchanged to change the magnification of the optical system; also the focus (group 4) 24 , Furthermore, with a suitable choice of the refractive powers and the distances of the groups 2 to 4 an adjustment of the focus position 15 with constant focus size or magnification possible.

10

Lichtleitfaserspitze

11

divergent laser beam

12

collimated laser beam

15

laser beam focus in nominal z position

18

laser beam focus with z-position correction without focus shift

19

laser beam focus without z-position correction with focus shift

21

first Lens group (collimator)

22

lens group

23

lens group

24

latest Lens group (focusing)

26

Beamsplitter for the laser radiation antireflex-coated

27

Beamsplitter highly reflective coated for the laser radiation

30

servomotor

31

linear guide

32

carriage

40

control with computing and storage unit

41

optical sensor

42

schematic Identification of the active surface of the sensor

43

optical Focus position sensor or autofocus sensor

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• EP 0365511 [0007]
• - EP 1380870 [0007]
• - JP 01122688 A [0008]
• GB 2354845A [0011]

Claims (15)

System for active readjustment of the focus position for optics for high-power laser radiation for laser material processing, consisting of the following components: a. Sensor for detection the focus position, b. Control computer that processes the sensor data and from this correction data for the movable axis of the optics calculated, c. Movable axis of optics to change or Correction of the focus position, wherein the movable axis realized is, either i. with a guiding machine as an axis, at whose control the correction data are transmitted, or ii. with an additional axis between guide machine and optics showing the correction of the focus position by shifting the entire optics makes, or iii. with one in the optics integrated additional axis, by means of which in the optics a lens or a partial lens system is movably mounted and so the focus position can be moved. System for active readjustment of the focus position for optics for high-power laser radiation for laser material processing, consisting of the following components: a. Means for detecting the instantaneous laser power, which is a data interface can handle what data about the current laser power receives from the parent controller, or around a sensor mounted in the optics of the laser power measures, z. B. a photodiode, the minimum but constant Fraction of the laser power receives, as well b. one Control computer processing the laser performance data, the temporal change calculates the focus position and from this correction data for the movable axis of the optics determines, as well as a c. movable Axis of the optics for changing or correcting the focus position, wherein the movable axis is realized, either i. With a guiding machine as an axis, on whose control the Correction data are transmitted, or ii. with a additional axis between guiding machine and Optics, which correct the focus position by moving the entire optics makes, or iii. with one in the optics integrated additional axis, by means of which in the optics a lens or a partial lens system is movably mounted and so the focus position can be moved. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that the means for detecting Data include an optical sensor, either for measurement the instantaneous intensity of the laser beam or for measurement the axial focus position is suitable, wherein the optical sensor receives a fraction of the power of the laser beam, detects the intensity of the entire beam cross section and thus provides a signal proportional to the power. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that the means for detecting Data include an optical sensor, either for measurement the instantaneous intensity of the laser beam or for measurement the axial focus position is suitable, wherein the optical sensor receives a fraction of the power of the laser beam, detects the intensity in the center of the beam and thus a provides signal proportional to the power density. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that the means for detecting Data include an optical sensor, either for measurement the instantaneous intensity of the laser beam or for measurement the axial focus position is suitable, wherein the optical sensor receives a fraction of the power of the laser beam, provides a dependent of the received power signal and a plurality of active areas distributed over the beam cross section has, with which the intensity distribution of the beam detected can be. Device for stabilizing the focal position in optics for high-power laser radiation for laser material processing with a controller, with means for detecting data and with an optics in which at least a part of the optical system is movably mounted in the axial direction and driven by a servomotor, characterized characterized in that in an existing collimator and focusing optics, the collimator or the focusing is axially adjustable and can be used to correct the focus position and the means for detecting data include an optical sensor, either for measuring the instantaneous intensity of the laser beam or for measurement the axial focus position on, wherein the optical sensor receives a fraction of the power of the laser beam, detects the intensity of the entire beam cross section and thus provides a signal proportional to the power. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that at one of collimator and focusing existing optics of the collimator or focusing is axially adjustable and usable to correct the focus position and the means for collecting data is an optical sensor include, either to measure the instantaneous intensity the laser beam or for measuring the axial focus position suitable is, wherein the optical sensor is a fraction of the power of Laser beam receives the intensity in the beam center recorded and thus a proportional power density signal supplies. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that at one of collimator and focusing existing optics of the collimator or focusing is axially adjustable and usable to correct the focus position and the means for collecting data is an optical sensor include, either to measure the instantaneous intensity the laser beam or for measuring the axial focus position suitable is, wherein the optical sensor is a fraction of the power of Laser beam receives, one of the received power dependent signal provides and several over the Beam cross section has distributed active surfaces, which the intensity distribution of the beam can be detected. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that in one of 4 lens groups existing optics, with the first group acting as a collimator the second group has a positive power, the third group a negative refractive power and the fourth group a positive refractive power has either the second or the third lens group axially is adjustable and is suitable for correcting the focus position and the means for collecting data include an optical sensor, either for measuring the instantaneous intensity of the Laser beam or for measuring the axial focus position suitable is, wherein the optical sensor is a fraction of the power of Laser beam receives the intensity of the whole Beam cross section recorded and thus a proportional to the power Signal supplies. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that in one of 4 lens groups existing optics, with the first group acting as a collimator the second group has a positive power, the third group a negative refractive power and the fourth group a positive refractive power has either the second or the third lens group axially is adjustable and is suitable for correcting the focus position and the means for collecting data include an optical sensor, either for measuring the instantaneous intensity of the Laser beam or for measuring the axial focus position suitable is, wherein the optical sensor is a fraction of the power of Laser beam receives the intensity in the beam center recorded and thus a proportional power density signal supplies. Device for stabilizing the focus position at Optics for high-power laser radiation for laser material processing with a controller, with means for collecting data and with an optics in which at least a part of the optical system in axially movable and is supported by a servomotor is driven, characterized in that in one of 4 lens groups existing optics, with the first group acting as a collimator the second group has a positive power, the third group a negative refractive power and the fourth group a positive refractive power has either the second or the third lens group axially is adjustable and is suitable for correcting the focus position and the means for collecting data include an optical sensor, either for measuring the instantaneous intensity of the Laser beam or for measuring the axial focus position suitable is, wherein the optical sensor is a fraction of the power of Laser beam receives, one of the received power dependent signal provides and several over the Beam cross section has distributed active surfaces, which the intensity distribution of the beam can be detected. Device according to one of the preceding claims, characterized in that the optical sensor is disposed behind a highly reflective deflection mirror and detects the transmitted residual radiation. Device according to at least one of the preceding Claims, characterized in that the optical sensor arranged next to an antireflection-coated Auskoppelspiegel is and detects the reflected residual radiation. Device according to at least one of the preceding Claims, characterized in that they are for the modification of workpieces, in particular the joining, Coating or cutting workpieces is suitable. Device according to one of claims 1 to 11, characterized in that the means for detecting the instantaneous laser power include a focus optical sensor, which is capable of delivering a signal that of the deviation the actual focus position to target focus position depends is.