Method and apparatus for compensating for beam angle variations of a laser beam generated by a diffractive optical element

Abstract

A method for compensating for beam angle variations of a beam of a laser beam generated by a diffractive optical element, and an arrangement for compensating for beam angle variations of a beam of a laser beam generated by a diffractive optical element.

Description

Technical Field

[0001] The present disclosure relates to a method for compensating for beam angle variations of a beam of laser beams having respective beam angles. The present application also relates to an arrangement for compensating for beam angle variations of a beam of laser beams having respective beam angles. Background Art

[0002] In application scenarios where a high degree of accuracy is required to know the beam angle, the wavelength of the laser can be stabilized, for example, by closed-loop control. US 4 737 798 A discloses a method for preventing mode hopping in a laser diode, wherein the stable operating temperature range of the diode is identified by the following steps: the laser diode bias current is reduced to a predetermined value, thereby reaching a first diode temperature level at which mode hopping occurs, and then the diode modulation current is increased to a predetermined value, thereby reaching a second diode temperature level at which mode hopping occurs. The diode bias and modulation current are monitored during operation of the diode, wherein when a predetermined diode bias current is reached, the diode is heated to increase the diode temperature and prevent the diode from reaching the first temperature level. This prevents the diode from completing a mode hopping. Therefore, when a predetermined diode modulation current is reached, the diode is cooled to reduce the diode temperature and prevent the diode from mode hopping at the second temperature level. Summary of the invention

[0003] It may be an aim to provide a simplified arrangement and method that does not require feedback control of the laser.

[0004] According to one aspect of the present application, a method for compensating for beam angle variations of laser beams having respective beam angles is proposed, comprising the following steps:

[0005] - generating a beam of light using a diffractive optical element;

[0006] - determining a beam angle value from at least one beam angle of a first subset of laser beams;

[0007] - detecting a light pattern projected by a second subset of laser beams;

[0008] - evaluating the light pattern, wherein the evaluation is performed taking into account beam angle variations of the beam angles of the second subset of laser beams based on the determined beam angle values.

[0009] The variation of the beam angle of each laser beam in the beam bundle deflected by the diffractive optical element is related to the variation of the wavelength of the underlying emitted laser light. By using the first subset of laser beams to determine the beam angle value, the variation of the beam angle of all generated beams is traceable and can advantageously be used for the evaluation of the detected light pattern of the second subset of laser beams simultaneously or offset in time to compensate for it. The determined beam angle value is not fed back into the laser electronics but is transmitted, for example, to a processing device for evaluating the light pattern using corresponding software, which performs the required calculations for evaluating the light pattern taking into account the variation of the beam angles of the beam angles of the second set of laser beams according to the determined beam angle value, such as for laser triangulation.

[0010] Although laser beams or laser diodes are mentioned in the context of the present disclosure, the skilled person will recognize that the solutions and embodiments presented herein are applicable to any type of coherent radiation or coherent light source, and therefore the term laser radiation will be understood as a synonym for coherent radiation. A diffractive optical element (DOE) as defined in the present disclosure can be used to generate multiple laser beams using only one laser beam from a laser source. The laser light from the laser beam is deflected into a specified beam angle by interference, so that a complex pattern or beam can be generated from one laser beam. The interference of coherent radiation (such as laser light) is wavelength-dependent, which means that the beam angle of the resulting laser beam and therefore the entire pattern are also wavelength-dependent. Ordinary laser diodes and other coherent beam sources do not usually emit laser light with a constant wavelength, because changes in parameters such as the diode current and diode temperature of the laser diode affect the emission wavelength of the light. In addition to stable temperature drifts, transient mode jumps can also occur. Changes in the laser wavelength result in changes in the beam angle of the laser beam deflected by the diffractive optical element, which can be advantageously compensated by the method. As a special case of a simple DOE, a grating, such as a line grating or a slit array, can be used.

[0011] According to an embodiment, a data set, such as a so-called look-up table with data, is used for evaluating the light pattern, wherein the data of the data set are adapted depending on the determined beam angle value. If the determined beam angle value deviates from a reference value, the data of the data set can be adjusted, for example, depending on the difference between the reference value and the determined beam angle value. The data of the data set can concern the reference value, as well as the specification of the beam position and the beam angle of the corresponding laser beam, i.e. the position vector and the direction vector of the laser beam, which can be recorded, for example, in a previous calibration step. Alternatively, taking into account the determined beam angle value, the recorded light pattern can first be modified to form a corrected light pattern, which can then be evaluated without further compensation.

[0012] The beam angle value is determined by at least one beam angle of one of the laser beams of the first subset of laser beams. In the case of only one laser beam, the beam angle value corresponds to the beam angle. In the case of a plurality of laser beams of the first subset of laser beams, the beam angle value can be formed in a suitable manner from the plurality of beam angles, for example as an average value. According to an embodiment, the beam angle value can be determined by detecting the beam angle of at least one laser beam of the first subset using at least one optical position sensor. If necessary, a plurality of optical position sensors can be used. Likewise, the beam angles of a plurality of laser beams can be detected with one optical position sensor. For example, the first subset of laser beams is selected so that under a change in the wavelength of the laser beams, the change in the beam angle of at least one laser beam of the first subset in a first of the two spatial directions is significantly greater than the change in the beam angle in a second of the two spatial directions. Thus, the change in the beam angle is approximately one-dimensional, which advantageously facilitates its determination. As long as the position sensor can still detect the laser beam, a change in the beam angle in a second spatial direction orthogonal to the first spatial direction can be tolerated. A one-dimensional optical position sensor can also be used if the sensor axis is aligned with a radial extending from the center point of the projected light pattern in the plane of the sensor. In the case of a wavelength change of the laser beams, the corresponding laser beams then undergo a beam angle change in both spatial directions, but the beams are only offset along the sensor axis, i.e. the projected laser spot will move along the sensor axis. When using a two-dimensional sensor, such as a matrix sensor, the first subset of laser beams can also be selected arbitrarily, since in the case of a wavelength change a change in the beam angle of at least one laser beam of the first subset is detected in both spatial directions.

[0013] The beam angle value may advantageously be determined based on a measurement of at least one optical position sensor and a distance of the diffractive optical element to the at least one optical position sensor. The measurement of the at least one optical position sensor and any other position sensor is a position deviation of a laser spot projected onto the optical position sensor by a respective at least one laser beam of the first subset of laser beams. With the known distance from the diffractive optical element to the at least one optical position sensor, the beam angle value may be calculated as an angular deviation from a reference value. The at least one optical position sensor may advantageously be fixedly arranged at a predetermined distance from the diffractive optical element.

[0014] According to another embodiment, beam angle values ​​are determined using two laser beam groups of a first subset, wherein the beam angles of the laser beams of the two laser beam groups are detected using two spatially separated optical position sensors. This may be advantageous because it allows detection of additional effects, such as beam pointing. The first subset may comprise more than one laser beam, wherein at least two laser beams have the same beam angle in one spatial direction and are detected by one and the same optical position sensor. Advantageously, the laser beams of each of the two laser beam groups may each have the same beam angle in one spatial direction and be detected by one and the same optical position sensor. The first subset of laser beams may be directed to at least one optical position sensor by means of a deflection device or a plurality of deflection devices.

[0015] Another aspect of the present application relates to an arrangement for compensating for beam angle variations of a beam of laser beams having respective beam angles, comprising

[0016] - a diffractive optical element for generating a light beam;

[0017] - a first sensor arrangement for determining a beam angle value from at least one beam angle of a first subset of laser beams;

[0018] - a second sensor arrangement for detecting a light pattern projected by a second subset of laser beams;

[0019] - a processing device for evaluating the light pattern, the processing device being adapted to evaluate the light pattern taking into account beam angle variations of the beam angles of the second subset of laser beams based on the determined beam angle values.

[0020] According to the above method, the arrangement can be used to compensate for beam angle variations of a laser beam having a corresponding beam angle generated by a diffractive optical element. The features of the method are similarly applicable to the arrangement, and vice versa.

[0021] According to an embodiment, the first sensor arrangement comprises at least one optical position sensor, in particular at least one position sensitive detector (PSD), which can measure the position of the light spot in one or two dimensions. For example, the first sensor arrangement has two spatially separated optical position sensors, in particular two position sensitive detectors. The at least one optical position sensor can be spatially positioned in such a way that in the case of a wavelength change of the laser beam, each laser beam of the first subset detected by the optical position sensor is subjected to a much larger beam angle change in the first of the two spatial directions than in the second of the two spatial directions, so that advantageously, a one-dimensional detection of the light spot is sufficient. A deflection device can be provided for deflecting the laser beam of the first subset in the direction of the first sensor arrangement.

[0022] The second sensor arrangement may be equipped with an optical position sensor or other optical sensor which detects the projected light pattern or records an image of the light pattern. The processing device for evaluating the light pattern may be a computer with a data carrier on which software is executed for evaluating the light pattern taking into account beam angle variations of the beam angles of the second subset of laser beams.

[0023] The first sensor arrangement may have a predetermined distance from the diffractive optical element, which distance is advantageously used to determine the beam angle value. The first sensor arrangement and the diffractive optical element may also be assigned to the lighting, for example arranged in a lighting housing, wherein only the second subset of laser beams emerges from the lighting or the lighting housing for projecting the light pattern.

[0024] Another aspect of the present application relates to the use of the aforementioned arrangement for laser triangulation, wherein an input laser beam is diffracted by a diffractive optical element to form a beam of laser beams having a corresponding beam angle, and the beam angle variation is compensated by the previously described method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Based on exemplary embodiments, the method and arrangement are explained below with reference to the accompanying drawings.

[0026] Figure 1 A measuring arrangement for three-dimensional measurement of an object is shown as an application example of the method for compensating for beam angle variations of a beam of a laser beam generated by a diffractive optical element;

[0027] Figure 2 is a schematic diagram of an arrangement for compensating for beam angle variations of a laser beam generated by a diffractive optical element; and

[0028] Figure 3 Is used to determine the basis Figure 2 The method of generating a second subset of laser beams at beam angle values ​​of the first subset of laser beams, and projecting a light pattern according to the method. DETAILED DESCRIPTION

[0029] Figure 1 A survey arrangement for three-dimensional survey of an object 7 is shown in a perspective schematic diagram, which can be used to measure the height and height profile of the object 7, for example by decoding a codeword defined by a light pattern 4. The device is described in more detail in European patent application No. 20180153.7 as an application example of a method for compensating for beam angle variations of a beam beam 12 of a laser beam generated by a diffractive optical element 9, see Figure 2 The method further comprises the following steps:

[0030] - determining a beam angle value from at least one beam angle Ai of the first subset 17 of laser beams,

[0031] - detecting the light pattern 4 projected by the second subset 18 of laser beams, and

[0032] - evaluating the light pattern 4 , wherein the evaluation is performed taking into account beam angle changes of the beam angles of the second subset 18 of the laser beams based on the determined beam angle values.

[0033] To execute according to Figure 2 The arrangement of the method has a first sensor arrangement 10 for determining a beam angle value from at least one beam angle of a first subset 17 of laser beams, a second sensor arrangement 16 for detecting a light pattern 4 projected by a second subset 18 of laser beams, and for evaluating the light pattern 4 taking into account beam angle changes of the beam angles of the second subset 18 of laser beams based on the determined beam angle values.

[0034] Figure 1 The survey arrangement shown in comprises a detection device 1 having a second sensor arrangement 16 for detecting a light pattern 4 projected by a second subset 18 of laser beams, for example, having an optical sensor for detecting the projected light pattern 4 or recording an image of the light pattern 4. The detection device 1 has an observation range 2, which can be appreciated in the present perspective view. The observation range 2 of the detection device 1 is indicated by a dashed line. The observation range 2 of the detection device 1 is fanned out in the direction of the X-axis and, to a lesser extent, in the transport direction T transverse to the X-axis. The survey arrangement also comprises an illumination 3 for projecting the light pattern 4 in the direction of a reference surface 5. The reference surface 5 is defined by the surface of a conveyor belt 6. The conveyor belt 6 is driven in the transport direction T. For example, an object 7 in the form of a package moves on the conveyor belt 6 in the transport direction T. The illumination 3 projects a light pattern 4 onto the conveyor belt 6 and the object 7 using a second subset 18 of the laser beams in a projection area 8, wherein the light pattern 4 can be in the form of an upper stripe in the direction of the X-axis. The projection area 8 is indicated by a dashed line. The object 7 is conveyed through the projection area 8 and the observation area 2. In the case of the object 7 being transported through the projection area 8, the projection area 8 and the observation area 2 are coplanar or overlap each other. This means that the inspection device 1 can always detect the light pattern 4 projected onto the object 7 in the area in which the object 7 is transported through the projection area 8. In this case, the observation area 2 extends outward in a fan shape in the transport direction T at least as far as the projection area 8. Therefore, the light pattern 4 is always located in the observation area 2 of the detection device 1.

[0035] Figure 2 FIG. 1 is a schematic diagram of an arrangement for compensating for a change in the beam angle of a beam beam 12 of a laser beam, the laser beam being generated by a diffractive optical element 9. The diffractive optical element 9 may be connected to Figure 1The diffractive optical element 9 may be associated with the illumination 3 in the light beam 12, for example, the diffractive optical element 9 may be arranged in the housing of the illumination 3. The light source 14 may emit the input laser beam 11 onto the diffractive optical element 9 (hereinafter referred to as DOE 9) via a deflection element such as a mirror. Through the DOE 9, the input laser beam 11 fans out to form a light pattern 4. When the laser beam 11 passes through the DOE 9, the beam is split into light beams 12 by interference. Each laser beam of the light beams 12 is deflected by a separate beam angle Ai relative to the input laser beam 11. The beam angle Ai is defined by the parameters of the DOE 9 and the incident light wavelength of the input laser beam 11. If the beam angle Ai of any laser beam of the light beam 12 is known, beam angle correction can be performed on all other laser beams of the light beam 12.

[0036] The laser beams of the light beam bundle 12 are divided into a first subset 17 of laser beams and a second subset 18 of laser beams. A first sensor arrangement 10 for determining a beam angle value from at least one beam angle of the first subset 17 of laser beams can be associated with the lighting 3, for example arranged together with a diffractive optical element 9 in a housing of the lighting 3, as in the exemplary embodiment shown. In this case, the laser beams of the first subset 17 do not leave the lighting 3, but only the laser beams of the second subset 18 for projecting the light pattern 4. A second sensor arrangement 16 for detecting the light pattern 4 projected by the second subset 18 of laser beams is associated with the detection device 1 ( Figure 1). A processing device 15 is provided for evaluating the light pattern 4 taking into account beam angle changes of the beam angles of the second subset 18 of the laser beams based on the determined beam angle values ​​of the first subset 17 of laser beams. In order to transmit the determined beam angle values ​​of the first subset 17 of laser beams from the first sensor arrangement 10 to the processing device 15, there is a connection schematically shown by a dashed line. The processing device 15 itself can be associated with the detection device 1 or the illumination 3 alternatively, or with neither the detection device 1 nor the illumination 3. The first sensor arrangement 10 comprises, for example, at least one optical position sensor, in particular at least one position-sensitive detector. In the illustrated exemplary embodiment, the first sensor arrangement 10 has two spatially separated position-sensitive detectors. Therefore, the beam angle values ​​are determined based on the two laser beam groups 17a, 17b of the first subset 17, wherein the beam angles of the laser beams of the two laser beam groups 17a, 17b are detected by two spatially separated optical position sensors of the first sensor arrangement 10. Therefore, the first subset 17 can include more than one laser beam. Furthermore, each of the two laser beam groups 17a, 17b may comprise at least two laser beams which, for example, have the same beam angle in a spatial direction and which can therefore advantageously be detected by one and the same optical position sensor of the first sensor arrangement 10. The at least one optical position sensor of the first sensor arrangement 10 is spatially positioned in such a way that, in the event of a change in the wavelength of the laser beams, each laser beam of the first subset 17 detected by the optical position sensor undergoes a much larger change in beam angle in a first direction of the two spatial directions than in a second direction of the two spatial directions. Thus, the optical position sensor advantageously only needs to detect the position of the laser beam in one direction. The optical position sensor of the first sensor arrangement 10 is used to detect mode jumps based on the detected laser beams of the first subset 17 and further to detect temperature drifts within a mode platform of the laser light source 14.

[0037] Combine the following Figures 1 to 3The method is explained in more detail. The second subset 18 of laser beams generated by the DOE 9 forms a light pattern 4 of, for example, 901 laser beams projected onto the object 7 to enable a three-dimensional measurement of the object surface of the object 7 when the object 7 or the package moves along the conveyor belt 6, for example during parcel sorting. Here, laser triangulation is used to determine the height pattern of the object 7, wherein the laser illumination 3 is arranged offset from the detection device 1. The projected light pattern 4 of the laser point is detected by the second sensor arrangement 16, and the position of the laser point is continuously analyzed at each detection or in each image. More details are described in document EP 2 728 305 A1. The principle of laser triangulation requires that the beam angles Ai of the laser beams of the second subset 18 are precisely known at any time or during each acquisition or image capture, if possible, because they are the basis for the distance calculation of the object 7 to be measured. For this purpose, a high-precision data set of all beam angles, such as a look-up table (LUT) (beam LUT) is generated in a calibration step before use. If fast data processing is secondary, the beam information can also be stored in other parameter data sets. As an example, if the deflection of a laser beam is considered in only one spatial direction, the following formula applies to all beam angles:

[0038] sin(Ai)=λ*ki (Formula 1),

[0039] wherein ki denotes the spatial frequency encoded in the surface structure of the DOE 9 and λ denotes the wavelength of the emitted laser light. Now, if the wavelength λ of the incident light changes, the beam angle of each outgoing laser beam of the light beams 12 also changes accordingly, possibly with the exception of the central laser beam which is not deflected due to its k value being zero. Therefore, the beam angle Ai of each deflected laser beam of the light beams 12 allows to infer the wavelength change and, by the known DOE parameter ki, the angle change of all other newly emerging laser beams. Therefore, it is only necessary to detect the beam angle value of at least one beam angle from the first subset 17 of laser beams in order to know the wavelength-dependent beam angle change of the laser beams generated by the DOE 9 of the second subset 18 of laser beams. This is then used in the evaluation of the light pattern 4, wherein the evaluation is performed taking into account the beam angle change of the beam angles of the second subset 18 of laser beams based on the detected beam angle values, for example by correcting a stored beam angle LUT for the current beam angle change.

[0040] For this purpose, for example, the DOE 9 is designed in such a way that two laser beam groups 17a, 17b are projected under the light pattern 4 for the three-dimensional measurement of the object 7, which is used to measure the beam angles of the laser beams of the first subset 17. The two laser beam groups 17a, 17b are each projected or deflected onto an optical position sensor of the first sensor arrangement 10. For example, a mirror not shown here can be used as a deflection element. For example, each of the laser beam groups 17a, 17b consists of three laser beams in close proximity. For example, a position sensitive detector (PSD) of the first sensor arrangement 10 is used as an optical position sensor. Alternatively, a line or matrix image sensor can also be used. In the following, the abbreviation PSD is also used as a representative of all applicable sensor types. Only one laser beam group 17a and only one PSD for detecting the beam angle already realize the basic function. Further advantages arise if the two laser beam groups 17a, 17b are used with beam angles Ai of different signs, i.e. deflected in opposite directions from the direction of the incident laser beam 11. If the two position sensors of the first sensor arrangement 10 detect two laser beam groups 17a, 17b after the same optical path length, in the case of a purely wavelength-dependent change in the beam angle Ai, changes of the same absolute value but opposite sign are recorded. In addition, if the beam angle Ai is subject to further influences before passing through the DOE 9, such as beam pointing or mechanical misalignment of the laser light source 14 or the deflection optical element (if applicable), these changes are perceived identically in magnitude and direction of movement on the two PSDs of the first sensor arrangement 10. It is therefore advantageous to distinguish between the influence of the wavelength and other influences. If it is assumed that other influences than the influence of the wavelength change are small, the necessary measured values ​​for correcting the beam LUT can already be recorded using the laser beams of the first subset 17 and the PSD of the first sensor arrangement 10. The laser spot movement recorded by the PSD of the first sensor arrangement 10 is converted into a beam angle change using the known setup geometry. The beam angle value represents the beam angle resulting from the beam angle change. The term beam angle value is used to distinguish it from the beam angle Ai of a single laser beam. From the perspective of the beam angle variation, the basic wavelength variation Δλ can be determined by formula 1, which can be used to calculate the variation of all beam angles Ai. With the information about the beam angle variation of all laser beams of the second subset 18, the beam LUT can be updated in software before processing each light mode 4. The updated beam LUT can be used to perform laser triangulation and adjust for stray effects of wavelength variation (and other effects, if any). Thus, beam angle variations caused by wavelength variations in the sub-nanometer range can be recorded, for example with a resolution of less than 0.5 nanometers, in particular about 0.2 nanometers. In order to determine the wavelength of the laser beam, the arrangement can also be used as an alternative and / or additional low-cost wavelength meter variant after prior calibration.

[0041] exist Figure 3 , a projected light pattern 4 is shown, wherein the columns of the light pattern 4 are formed in the direction of the X-axis. Below the actual light pattern 4, two laser beam groups 17a, 17b of the first subset 17 are shown. These laser beam groups each have three laser beams, whose light spots are displayed as measurement points 13 on the position sensitive detector of the first sensor arrangement 10. For example, the measurement points 13 can be arranged adjacent to each other in the Y-axis direction perpendicular to the measurement axis of the PSD. Since there is no need to adjust the PSD exactly to a single laser point, the assembly is simple and fast. The PSD of the first sensor arrangement 10 is aligned in such a way that only a measurement along the X-axis occurs, i.e. a one-dimensional shift of the beam angle change caused by the wavelength change. When the determined beam angle value deviates from the reference value, a compensation of the beam LUT of the beam angle Ai is performed using a computer program of the processing device 15 for evaluating the light pattern 4 by adjusting the data set according to the difference between the reference value and the determined beam angle value.

[0042] mark

[0043] 1. Testing equipment

[0044] 2 Scope of inspection

[0045] 3 lighting

[0046] 4 Light Patterns

[0047] 5 Reference plane

[0048] 6 Conveyor Belt

[0049] 7 Objects

[0050] 8 Projection area

[0051] 9 Diffractive Optical Element, DOE

[0052] 10 First sensor array

[0053] 11 Input laser beam

[0054] 12 Beam

[0055] 13 Measurement points

[0056] 14 Laser source

[0057] 15. Processing Equipment

[0058] 16 Second sensor array

[0059] 17 The first subset of laser beams

[0060] 17a, 17b Laser beam group

[0061] 18 Second subset of laser beams

[0062] XX axis

[0063] YY Axis

[0064] T Transport direction

[0065] A i Beam Angle

Claims

1. A method for compensating for beam angle variations of laser beams having respective beam angles, comprising the following steps: - generating the light beam using a diffractive optical element; - determining a beam angle value from the beam angle of at least one laser beam of the first subset of laser beams; - detecting a light pattern projected by a second subset of said laser beams, - evaluating the light pattern, wherein the evaluating is performed taking into account beam angle variations of the beam angles of the second subset of the laser beams based on the determined beam angle values, It is characterized in that the first subset of the laser beams is selected so that when the wavelength of the laser beams changes, the beam angle change of at least one laser beam of the first subset in a first direction of two spatial directions is significantly greater than the beam angle change in a second direction of the two spatial directions.

2. The method according to claim 1, characterized in that A data set with data is used to evaluate the light pattern, wherein the data are adapted as a function of the determined beam angle value.

3. The method according to claim 2, characterized in that In case the determined beam angle value deviates from the reference value, the data of the data set are adjusted according to the difference between the reference value and the determined beam angle value.

4. The method according to claim 1, characterized in that The detected light pattern is modified taking the determined beam angle value into account to form a corrected light pattern, and the corrected light pattern is evaluated.

5. The method according to any one of claims 1 to 4, characterized in that At least one optical position sensor is provided for determining said beam angle value by detecting a beam angle of at least one laser beam of said first subset of said laser beams.

6. The method according to any one of claims 1 to 4, characterized in that The beam angle value is determined using two laser beam groups of the first subset of the laser beams, wherein the beam angles of the laser beams of the two laser beam groups are detected using two spatially separated optical position sensors.

7. The method according to claim 5, characterized in that The first subset of laser beams comprises more than one laser beam, wherein at least two of the laser beams have the same beam angle in one spatial direction and are detected by one and the same optical position sensor.

8. The method according to claim 5, characterized in that The beam angle value is determined based on a measurement of the at least one optical position sensor and a distance from the diffractive optical element to the at least one optical position sensor.

9. An arrangement for compensating for beam angle variations of a beam of a laser beam having a corresponding beam angle, comprising: - a diffractive optical element for generating a beam of the laser beam; - a first sensor arrangement for determining a beam angle value from said beam angle of at least one laser beam of said first subset of laser beams, said first sensor arrangement comprising at least one optical position sensor; - a second sensor arrangement for detecting a light pattern projected by a second subset of said laser beams; - a processing device for evaluating the light pattern, wherein the processing device is adapted to evaluate the light pattern taking into account beam angle variations of the beam angles of the second subset of laser beams based on the determined beam angle values, It is characterized in that the at least one optical position sensor is spatially positioned so that when the wavelength of the laser beam changes, the beam angle change of each laser beam of the first subset of laser beams detected by the at least one optical position sensor in a first direction of two spatial directions is significantly greater than the beam angle change in a second direction of the two spatial directions.

10. The arrangement according to claim 9, characterized in that The at least one optical position sensor is at least one position sensitive detector.

11. The arrangement according to claim 9, characterized in that The first sensor arrangement comprises two spatially separated optical position sensors.

12. The arrangement according to claim 10, characterized in that The at least one optical position sensor comprises two position sensitive detectors.

13. An arrangement as claimed in any one of claims 9 to 12, characterised in that A deflection device is provided for deflecting the laser beams of the first subset in the direction of the first sensor arrangement.

14. An arrangement as claimed in any one of claims 9 to 12, characterised in that The first sensor is arranged at a predetermined distance from the diffractive optical element.

15. An arrangement as claimed in any one of claims 9 to 12, characterised in that Both the first sensor arrangement and the diffractive optical element distribute an illumination, wherein only a second subset of the laser beams emerges from the illumination for projecting the light pattern.

16. Use of an arrangement as claimed in any one of claims 9 to 15 for laser triangulation, wherein an input laser beam is diffracted by a diffractive optical element to form a beam of laser beams having corresponding beam angles, and beam angle variations are compensated by a method as claimed in any one of claims 1 to 8.

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