Method for measuring a laser beam

Abstract

A method for measuring a laser beam, in which the beam intensity and / or the wavefront (11) of the laser beam can be determined by means of at least one detector (50), wherein a partial beam (30) is coupled out from an input beam (10) to be measured by means of a freely programmable beam shaper (40) and the partial beam (30) is supplied to the detector (50) for analysis and a remaining output beam (20) can be used further, wherein in a measurement sequence the input beam (10) is successively measured by sequential measurement of offset partially overlapping partial beams (30) or sequential measurement of offset adjacent partial beams (30), characterized in that the wavefront (11) of the input beam (10) to be measured is determined by means of the detector (50).wherein, to determine the wavefront (11) of the input beam (10) to be measured, a phase distribution in the input beam (10) is calculated from an exact detector beam position (52) of each of the partial beams (30) on the detector (50) and a programmed phase function (42) which determines the deflection angle of each of the partial beams (30) from the input beam (10).

Description

State of the art

[0001] The invention relates to a method for beam measurement of a laser beam, in which the beam intensity and / or the wavefront of a laser beam can be determined by means of at least one detector.

[0002] In laser material processing (laser ablation, welding, soldering, cleaning, drilling, sintering, melting, etc.), focused laser beams with a Gaussian intensity distribution are typically used. However, for many of these processes, it is highly advantageous to adapt the intensity distribution in the processing plane to the process. Beam shaping in the processing plane offers enormous optimization potential for laser process development.

[0003] To shape the intensity distribution of a laser beam, either its phase, its amplitude, or both must be modulated. Accordingly, there are phase modulators, amplitude modulators, or phase and amplitude modulators. The major disadvantage of amplitude modulators (e.g., DMD micromirror arrays) is that when used for beam shaping, a portion of the laser radiation from the original beam is usually blocked, thereby reducing the energy efficiency of the overall system. The advantage of phase modulators is that they do not affect the amplitude of the original beam, allowing (almost) all of the energy to be used for the laser processing. Phase modulators, in turn, are based on two different principles – the principle of refraction and the principle of diffraction. Accordingly, there are refractive and diffractive beam formers.The former are quite limited in their beam shaping capabilities: Primarily, only simple and mostly axisymmetric beam shapes can be generated, such as so-called top hat beams, Bessel beams, Airy beams, donuts, etc. Complex geometries, especially those that lack rotational or rectangular symmetries, require the use of freeform surfaces. Corresponding design and manufacturing methods are already being developed but are not yet industrial standard. Diffractive beam formers, on the other hand, offer many more possibilities for beam shaping and beam splitting, since the corresponding micro-optical structures can be manufactured using lithographic processes, injection molding, or embossing, for example, and calculated using established phase retrieval algorithms. Furthermore, switchable beam formers, e.g. based on liquid crystal technology or micromirror arrays, are increasingly available on the market.

[0004] Diffractive beam shapers are usually 1D or 2D array structures that impose a discretized phase delay (phase distribution) on the incident (unshaped) laser beam. Changing the phase distribution of the incident laser beam also changes / modulates its intensity distribution in the Fourier plane (focal plane). Common diffractive beam shapers include so-called diffractive optical elements (DOEs), which are made of glass or plastic and incorporate a fixed, unchangeable diffraction structure. Also known are flexible / programmable beam shapers such as spatial light modulators (SLMs), preferably liquid crystal-based phase modulators with birefringent liquid crystals.

[0005] To achieve optimal laser beam adjustment, precise knowledge of the laser beam initially used is crucial. For this reason, numerous methods and devices have been developed to measure a laser beam's properties, such as amplitude distribution, wavefront, polarization, wavelength, propagation direction, etc.

[0006] There are many solutions, especially for determining the intensity distribution of a laser beam in its cross-section at a point along its propagation axis: - Camera-based systems, e.g. with CMOS / CCD chips, whose pixels can detect the intensity distribution in the beam cross-section with spatial resolution. - Pyro cameras - So-called slit profilers or slit scanners, which “scan” the beam cross-section with a small aperture behind which the transmitted laser power is measured. - Complete systems with the imaging of the input beam onto a camera and the simultaneous measurement of laser power (e.g. PRIMES MicroSpot).

[0007] There are also numerous methods and devices for determining the wavefront of a laser beam. Examples include a Hartmann-Shack sensor based on microlens arrays and a beam wave sensor from PhaseView, which can determine both the wavefront and the intensity distribution in the beam cross-section.

[0008] The disadvantage of these beam profiling systems is that an attenuator is required when measuring high-power laser beams. If beams with a large diameter (e.g., a raw beam) are also being examined, a beam reducer is often required. Furthermore, two different systems are usually required when measuring the raw beam and its focused image: A raw beam can be a few millimeters in diameter. However, when focused, a focus spot with a diameter in the µm range must be captured.

[0009] In the device for real-time monitoring of a laser's beam profile disclosed in DE 196 00 978 A1, a portion of the laser beam to be monitored is extracted using a beam splitter and fed to an optical correlator. The optical correlator contains a diffractive element configured to match the laser's desired beam profile. If the laser's beam profile matches the desired beam profile, the optical correlator emits a correlation peak (plane wave). If the beam profile deviates from the desired beam profile, a diffuse diffraction pattern is created. The optical correlator can thus be used to monitor the laser's beam profile during operation. However, it does not allow for flexible measurement of the beam profile.

[0010] The measurement of a laser beam is also known from the publicly available paper by YANG, H.; ROBERTSON, B. ; CHU, DP entitled "A non-intrusive in situ method of optical beam profiling in LCOS-based optical fiber switches. (Published in Optics and Lasers in Engineering, Vol. 51, 2013, No. 7, pp. 916-920. - ISSN 0143-8166). This describes the measurement of a beam by a gridded determination of local intensity values ​​within the beam cross-section. In this process, a partial section of an output beam directed at an SLM (Spatial Light Modulator) is masked out by the SLM by deflection into a "dump port", so that a beam cross-section remains that is reduced by the partial section.The reduced beam cross-section is successively changed by shifting the masked section across the beam cross-section in a linear motion, with each change in voltage at the SLM being determined based on the respective reduced beam cross-section. The resulting voltage changes allow the overall radiation profile of the output beam to be determined.

[0011] Published patent application US2007 / 0052694 A1 discloses a device and method for measuring amplitude and phase fluctuations in a spatially coherent light beam. A beam of coherent light impinges on a spatial array of phase modulation elements exhibiting a pixelated first phase distribution. Within a measurement region of the spatial array, the phase distribution is changed to a new value, for example, by flashing a single pixel, while maintaining the first phase distribution outside the measurement region. The intensity change resulting from the change in the phase distribution is then determined.

[0012] The object of the invention is therefore to measure a laser beam profile without the above-mentioned disadvantages. Disclosure of the invention

[0013] The problem concerning the method is solved by the features of claim 1.

[0014] According to the invention, a partial beam is coupled out of an input beam to be measured by means of a freely programmable beam former, the partial beam is fed to the detector for analysis, and a remaining output beam can be used further, wherein the input beam is successively measured in a measurement sequence by sequentially measuring offset, partially overlapping (sequentially coupled out) partial beams or sequentially measuring offset, adjacent (sequentially coupled out) partial beams.

[0015] With this approach, various procedural strategies can be implemented, which can also be selected and combined depending on the situation, as explained in the description of the exemplary embodiments. For example, the output surface of the partial beams on the freely programmable beamformer can be selected to be more or less large, and the partial beams can be output with more or less overlap or without any overlap. A large output surface with a small overlap is advantageous for quickly estimating how the power of the input beam is roughly distributed on the beamformer, as it provides a low-resolution beam profile measurement with just a few measurements (e.g., 2 to 10). A measurement with small output surfaces and little or no overlap provides very good (optimal) measurement results for every beam shape, as the measurement resolution depends directly on the size of the measurement surface.

[0016] In a preferred method variant, a phase or amplitude modulator is used as the beam former. These were mentioned above, with the possibility of free programmability being particularly advantageous.

[0017] It is particularly advantageous in terms of application effort if the detector determines the intensity distribution and / or the wavefront of the input beam to be measured. The intensity distribution can be measured using the camera-based systems mentioned above, so-called pyro cameras, slit scanners, or complete systems for measuring the intensity distribution and laser power. For determining the wavefront of the laser beam, a Hartmann-Shack sensor based on microlens arrays or a beam wave sensor, for example, are suitable, as they can determine both the wavefront and the intensity distribution in the beam cross-section.

[0018] For determining both the intensity distribution and the wavefront, a beam profile camera can be used as a detector, which is particularly advantageous. This allows beam intensities to be determined very precisely, depending on the position.

[0019] To determine the wavefront of the input beam to be measured, the invention calculates a phase distribution in the input beam from a precise detector beam position of each partial beam on the detector and a programmed phase function that determines the deflection angle of each partial beam from the input beam. This allows for a high degree of accuracy in determining the intensity distribution.

[0020] In order to be able to determine the detector beam position exactly, a particularly advantageous method variant provides for the use of a detector with high spatial resolution and / or imaging optics for focusing the partial beam.

[0021] An advantageous design for special applications involves the beam former extracting only a small portion of the input beam, e.g., a maximum of 5% of the input beam's radiant power, and modulating the beam former's control to successively measure the entire input beam. Depending on the desired accuracy, the partial beam can also contain significantly smaller portions of the input beam, for example, a maximum of 0.1% to 1%. This also allows for the analysis of relatively large beam diameters with high spatial resolution.

[0022] A preferred application of the method, as described above with its variants, involves use in laser processing systems for laser ablation, laser drilling, laser marking, laser soldering or laser welding, laser cutting, laser sintering and deposition welding, laser cleaning, laser hardening, laser remelting, laser alloying and dispersing, or laser polishing. Perfect beam quality with homogeneous beam shaping is essential here. The method according to the invention, with regard to beam measurement of the input beam, enables optimal beam shaping to achieve high beam quality in the processing plane in the aforementioned processes.

[0023] Beam measurement methods are generally carried out, for example, by a beam measurement device. More generally, such a beam measurement device can comprise at least one freely programmable beam former and a computer unit with which signals from the detector can be processed and with which the beam former can be controlled. A partial beam can be filtered out of an input beam to be measured using the beam former and fed to the detector for analysis. A measurement sequence can be specified, under which offset overlapping partial beams can be measured sequentially or offset directly adjacent partial beams can be measured sequentially, and the input beam can be successively analyzed from the measurement.

[0024] It should be noted in general that such a beam measurement device, or essential components thereof, can be implemented as a standalone solution in the form of an independent beam profile or wavefront sensor, which can be used to analyze beam profiles with large diameters. However, it can also be an integral component of a laser processing system, where an input beam can be analyzed and, based on the results of the analysis, a beam with improved properties can be shaped. This thus represents a measurement system that can be integrated into a laser processing optics system with a programmable beam shaper.

[0025] Furthermore, it should be generally mentioned that such a beam measurement device or essential parts thereof can be combined in a device for determining the beam position of a laser beam. Such a device for determining the beam position is described in the applicant's as yet unpublished document with the internal file number R.370388.This describes a device and a method for determining the beam position of a laser beam, wherein it is provided that a beam position can be determined using a beam splitter for coupling out a secondary beam from the laser beam and an optical position sensor arranged in the secondary beam, wherein a beam former is arranged in the beam path of the secondary beam or in the beam path of the laser beam upstream of the beam splitter, that the intensity profile of the secondary beam is shaped by the beam former and imaged onto the optical position sensor, that the intensity distribution of the shaped secondary beam and / or the position of the focus of the shaped secondary beam on the position sensor can be determined using the optical position sensor, and that the device is designed to determine the beam position of the laser beam from the intensity distribution detected by the optical position sensor and / or from the position of the focus of the shaped secondary beam.The previously described method according to the invention enables the precise detection of a laser beam alignment error. Due to the similarity in the system design, such a combination offers particular advantages in terms of application complexity.

[0026] The invention is explained in more detail below using an exemplary embodiment illustrated in the figures. They show: Fig. 1 shows a schematic representation of the measuring principle of a beam measuring device, Fig. 2 shows a schematic representation of the principle of an independent beam measuring device, Fig. 3 shows a further schematic representation of the principle of a beam measuring device integrated in a laser processing system, Fig. 4 a beam former of the beam measuring device with incident input beam, outgoing output beam, different coupling surfaces of partial beams and overlap in a schematic representation and Fig. 5 beam formers with different pixel structures and matching output surfaces in a schematic representation.

[0027] Fig. 1 schematically shows the measuring principle of the inventive idea: In a beam measuring device 1, an input beam 10 to be measured falls with its wavefront 11 onto a programmable beam former 40, wherein in the example shown, the beam former 40 is represented as a reflective component.

[0028] The beam former 40 can be programmed to successively couple in a coupling area 31 (e.g. with the coordinates X TS , Y TS) directs a partial region (partial beam 30) of the input beam 10 onto a detector 50, with the remaining residual beam remaining available as output beam 20 for laser processing. The beam shaper 40 should preferably be designed discretely, e.g., as a pixel array of liquid crystals (LCoS-SLM) or as a micro-mirror array (DMD). If the entire beam is scanned, a discrete beam profile can be created. The possible resolution of the measurement therefore depends on the resolution of the beam shaper 40. The beam shaper 40 and the detector 50 each have a corresponding beam shaper coordinate system 41 and detector coordinate system 51, respectively.

[0029] The choice of beam former 40 is also based on the requirements for the measured quantity, intensity distribution and / or wavefront 11. An amplitude modulator as beam former 40 can be used to measure the intensity distribution, but not the wavefront 11. A phase modulator, on the other hand, can be used to determine both the intensity distribution and the wavefront 11.

[0030] The choice of detector 50 depends on the information required: If only the knowledge of the intensity distribution in the input beam 10 is required, the following detectors 50 can be selected, for example: - Power meter (photodiode, laser power meter, etc.) - Beam profile camera, where the incident intensity is integrated across the camera chip to determine the intensity of the deflected beam. - Pyrometer

[0031] If knowledge of the wavefront 11 of the input beam is required, position-sensitive detectors must be used: - Beam profile camera - Matrix sensors / photodiode array

[0032] Therefore, detectors 50 that can detect the intensity in a position-dependent manner are suitable for determining both the intensity distribution and the wavefront 11 of the input beam 10. A beam profile camera is the preferred choice.

[0033] How the intensity profile is measured is explained in the Fig. 1. A further step is required to determine the wavefront distribution in the input beam 10. If a partial beam 30 from the incident beam is directed onto the detector 50 using a phase modulator, its position on the detector (detector beam position 52) is P detect depending on the phase function programmed on the phase modulator 42 Φ program, which causes a deflection of the main beam by a certain angle α, and from the phase function of the incident beam ϕ beam : Pdetect=f(ϕbeam,ϕprogram)

[0034] So if the position of the partial beam on the detector (detector beam position 52 P detect ) is measured and the phase function programmed on the phase modulator 42 ϕ program is known, the original phase distribution in the input beam ϕ beam be recalculated: ϕbeam=f(Pdetect,ϕprogram)

[0035] The accuracy of determining the intensity distribution is likely to be high, since only the power needs to be determined with sufficient measurement accuracy. This is achieved with most power meters.

[0036] For the precise determination of the wavefront distribution in the input beam 10, the position of the decoupled (small) beam (partial beam 30) on the detector 50 must be determined very precisely. For this purpose, either the selected detector 50 must have a sufficiently high resolution, or the deflected partial beam 30 must be guided to the detector 50 using an imaging optics installed between the beam former and the detector. A simple focusing lens can serve as the imaging optics 60, as shown in the Fig. 2 and Fig. 3 is shown schematically.

[0037] The presented idea can be implemented as a stand-alone beam profiler and wavefront sensor. This variant can be used to measure beam profiles with large diameters and can be used flexibly. A possible implementation is shown in Fig. 2. Here, the beam to be measured (input beam 10) is guided to the beam former 40. From the beam, discrete partial beams 30 are gradually deflected onto the detector 50, focused onto the plane of the detector 50 using the above-mentioned imaging optics 60, and measured for their power and position properties (corresponding to the intensity distribution and the wavefront). Since only a very small portion of the laser radiation is required at any given time during the measurement, the remaining radiation can be used as output beam 20 for further processes, e.g., for laser material processing. The unused portion of the radiation can also be blocked, e.g., in a beam trap (in Fig. 2 not shown). A computer unit 70, which can be part of the beam measurement device 1 or part of a higher-level laser processing system, serves for control and evaluation.

[0038] Beam shapers 40 are already being used in some laser systems and optical systems, for example, to optimize laser processing. In certain cases, it is necessary to measure the raw beam in such systems according to its intensity distribution and wavefront properties. This is especially necessary when the beam shapers require these beam properties as input information for calculating the output beam shape in the processing plane. In such systems, the existing beam shapers can also be used to measure the beam profile, as is the case with Fig. 3 schematically shows a system-integrated beam profile measurement. This allows, for example, the system to be adapted to varying input beams.

[0039] It is advisable to position the detector 50 shortly before the laser beam is coupled out of the processing optics, which would result in the errors and inaccuracies that occur between the beam former 40 and the beam exit in the other optics being recorded by the detector 50. The other optics represent a black box, which in Fig. 3 is shown as an optical system 90, which can be calibrated by the detector 50 arranged only after them.

[0040] In the example shown, the input beam 10 is guided on the input side within the beam measurement device 1 through a beam former 40, which is designed, for example, as a transmissible component, wherein the partial beam 30 to be measured is guided with the main beam through the optical system 90 and is then focused onto the plane of the detector 50 via a beam splitter 80 and the imaging optics 60. In this case, the partial beam 30 is already decoupled from the main beam or input beam 10 at the beam former 40. The partial beam 30 does not run parallel to the main beam or input beam 10, as is the case with the Fig. 3 is shown only schematically. The remaining residual beam can be used as output beam 20 for the laser process, whereby the beam measurement can be performed offline or online. If the output beam 20 is not needed, it can be redirected into a beam trap 100. A computer unit 70 is also used here for control and evaluation.

[0041] As mentioned at the beginning, the described method offers various measurement strategies that can be selected and combined depending on the situation in order to describe the intensity distribution of the input beam 10 using the programmable beam former 40 as accurately as possible or with an effort appropriate to the situation.

[0042] A number of partial beams 30, each with < 100% of the total power, are successively coupled out of the programmable beam former 40 and directed onto the detector 50 of a power meter as shown in Fig. 1. The position X TS , Y TSand the coupling surface 31 of the coupled partial beam 30 at the beam former 40 must always be fixed with the desired measurement accuracy. The measurement accuracy is in the order of magnitude of the resolution of the beam former 40. If, for example, a so-called spatial light modulator (SLM) based on LCD technology is used as the beam former 40, the resolution is limited by the pixel size of the SLM (usually 5 µm - 50 µm). The position X TS and Y TS and output coupling area 31 of the partial beam 30 on the beam former 40 are initially stored together with the measured power of the partial beam 30. At the end of the measurement process, the intensity distribution of the input beam 10 on the beam former 40 is reconstructed or combined from the measurement data.

[0043] In the measuring method, various measuring strategies can be carried out under appropriate control by means of a control device or using the computer unit 70. To select the measuring strategy, different sized and / or differently shaped output surfaces 31 on the programmable beam former 40 can be selected under appropriate control and it can also be specified whether the output surfaces 31 of the successively output partial beams 30 (directly) adjoin one another or have a more or less large overlap 31.1, as can be seen from the Fig. 4 and Fig. 5. In Fig. 4 shows, by way of example, a first (1a), second (2a) and third (3a) coupling-out surface 31', 31", 31''' as well as an overlap 31.1 of the third coupling-out surface 31''' with the first coupling-out surface 31'.

[0044] In Fig. 5 shows an output surface 31 adapted to a hexagonal pixel structure (left illustration) and a rectangular or square pixel structure (right illustration) of the beam former 40 as an example.

[0045] For example, four measurement strategies can be distinguished with a large coupling-out area (e.g. 25% to <100% of the total area of ​​the beamformer 40), a small coupling-out area (e.g. <25% of the total area of ​​the beamformer 40) as well as a large overlap 31.1 (25% to <100%) and a small to no overlap (<25%).

[0046] In a first measurement strategy (1A), a measurement is performed with a large output coupling area 31 or a measurement area with a large overlap 31.1, resulting in many measurement points, thus achieving high measurement resolution and thus accuracy with a moderate amount of time. This measurement strategy is well suited for measuring medium-sized input beams 10 (compared to the active area of ​​the beam former 40).

[0047] In a second measurement strategy (1B), a large output coupling area 31 is selected with little or no overlap 31.1. This measurement strategy allows for a quick estimate of the approximate power distribution of the input beam 10 across the beam former 40. With a small number of measurements (e.g., 2-10), this measurement strategy provides a low-resolution beam profile measurement with relatively low measurement effort.

[0048] In a third measurement strategy (2A), a large number of measurement points are generated with a small coupling-out area 31 or measurement area and a large overlap 31.1. Due to the high number of measurements, the measurement time is longer. Due to the high measurement resolution and the large number of measurement points, any measurement errors that may occur can be minimized by subsequent high-frequency filtering.

[0049] A fourth measurement strategy (2B) with small output coupling surfaces 31.1 (similar to measurement strategy 1A) achieves high accuracy at high resolution, although the measurement requires a longer measurement time. This measurement strategy delivers a very good (optimal) measurement result for any shape of the input beam 10, since the measurement resolution depends directly on the size of the output coupling surface 31 or measurement surface. This measurement strategy is preferable to measurement strategy 1A, especially for very large and very small beams. If the size of the input beam 10 corresponds almost to the entire area of ​​the beam former 30, large output coupling surfaces 31 cannot be used, since they cannot image the edge region of the input beam 10 accurately enough. For small input beams 10, large output coupling surfaces 31 cannot determine the position of the input beam accurately enough.

[0050] A more detailed categorization of the measurements than the one above is also possible, e.g. into large, medium, medium-small and small coupling-out areas 31 or overlaps 31.1.

[0051] Furthermore, a combination of different measurement strategies is also possible. For example, the fast measurement strategy 1B can be used to estimate the approximate position of the input beam 10 on the beam former 40. Subsequently, the output coupling area 31 or the measurement area can be reduced and scanned more finely using measurement strategy 1A or 2B.

[0052] In addition to the size of the coupling-out surface 31 or measuring surface and the overlap 31.1 between the coupling-out surfaces 31, the shape of the coupling-out surface can also be varied (see Fig. 5). Optimization for the beam former 40 is sensible: If a spatial light modulator based on LC display technology is used, in which the pixels are rectangular, it makes sense to also design individual output surfaces 31 rectangular. For beam formers 40 with hexagonal pixels, other shapes of output surfaces 31 may be more appropriate, such as triangular, hexagonal, etc. (see Fig. 5). The sequence of measurements with individual output surfaces 31 can vary. Rectangular output surfaces 31 can, for example, be alternated in a meandering pattern. Triangular output surfaces can be rotated around the tip. An optimal combination of different measurement strategies can optimize the measurement time.

[0053] The detector 50 or the power meter should be selected depending on the measurement strategy: For measurement strategy 1A, a unit should be used that can measure the total power of the input beam, but can also measure the smaller powers with sufficient accuracy. For measurement strategy 2B, a power meter can be used that can only measure lower power levels, since the entire line is never decoupled. Such devices can measure faster because they are less sluggish.

[0054] The presented method can be used in laser processing systems equipped with beam shapers 40, where precise beam measurement during beam shaping is essential. This can significantly improve the quality of beam shaping.

[0055] The application areas for the concept described above are diverse. In principle, this method can be used in all known laser processing techniques, especially micromachining. Examples include laser welding, laser polishing, laser ablation, marking, drilling, laser cleaning, etc.

Claims

[1] Method for beam measurement of a laser beam, in which the beam intensity and / or the wavefront (11) of the laser beam can be determined by means of at least one detector (50), wherein a partial beam (30) is coupled out of an input beam (10) to be measured by means of a freely programmable beam former (40) and the partial beam (30) is fed to the detector (50) for analysis and a remaining output beam (20) can be further used, wherein the input beam (10) is successively measured in a measurement sequence with sequential measurement of offset partially overlapping partial beams (30) or sequential measurement of offset adjacent partial beams (30), characterized bythat the wavefront (11) of the input beam (10) to be measured is determined by means of the detector (50), wherein, in order to determine the wavefront (11) of the input beam (10) to be measured, a phase distribution in the input beam (10) is calculated from a precise detector beam position (52) of each of the partial beams (30) on the detector (50) and a programmed phase function (42) which determines the deflection angle of each of the partial beams (30) from the input beam (10). [2] Method according to claim 1, characterized by that a phase or amplitude modulator is used as the beam former (40). [3] Method according to one of claims 1 or 2, characterized by that the intensity distribution of the input beam is determined by means of the detector (50). [4] Method according to one of the preceding claims, characterized bythat a detector (50) with high spatial resolution and / or an imaging optics (60) are used to focus the partial beam (30). [5] Method according to one of claims 3 or 4, characterized by that a beam profile camera is used as detector (50). [6] Method according to one of the preceding claims, characterized by that a small part of the input beam (10) with a maximum of 5% of the radiant power of the input beam (10) is coupled out by means of the beam former (40) and the entire input beam (10) is successively measured by modulating the control of the beam former (40). [7] Use of the method according to one of the preceding claims in laser processing systems for laser ablation, laser drilling, laser marking, laser soldering or laser welding, laser cutting, laser sintering and build-up welding, laser cleaning, laser hardening, laser remelting, laser alloying and dispersing or for laser polishing.

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