Laser device and method for processing at least one workpiece by means of at least one laser beam

Abstract

The invention relates to a laser device (10) for processing, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14), having features of claim 1, and to a method for processing, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14), having features of the additional independent claim.

Description

[0001] Title: Laser device and method for processing at least one workpiece by means of at least one laser beam

[0002] Description

[0003] The invention relates to a laser device for machining at least one workpiece by means of at least one laser beam having the features of claim 1 and to a method for machining at least one workpiece by means of at least one laser beam having the features of the independent claim.

[0004] When laser welding at least two components, CW (continuous wave) lasers with a constant power over the duration of the laser welding are usually used for deep welding. In particular when deep welding metallic materials with a low viscosity, instabilities can arise in the welding area, especially in the so-called keyhole. This can result in spatter, pores and / or an irregular weld depth, for example. To reduce such instabilities, several laser beams can be superimposed. However, this cannot eliminate all instabilities, especially with metallic materials with low viscosity.

[0005] It is therefore an object of the present invention to provide a laser device and a method for processing, in particular laser welding, at least one workpiece by means of at least one laser beam, wherein the above disadvantages are eliminated.

[0006] The above object is achieved by a laser device for machining at least one workpiece by means of at least one laser beam having the features of claim 1. The machining may involve laser welding.

[0007] The laser device is configured to generate the laser beam and focus it on the workpiece such that the laser beam creates a laser spot on the workpiece. The laser spot has a core region, in particular a circular one, and a ring region, in particular a ring-shaped one. An average laser power density in the core region is higher than an average laser power density in the ring region.

[0008] The laser device is also designed to vary the average laser power density in the core area with a variation frequency of at least 50 kHz (kilohertz) and a variation amplitude of at least 10% of the average laser power density of the core area. Alternatively or additionally, the laser device is designed to vary the average laser power density in the ring area with a

[0009] A variation frequency of at least 50 kHz and a variation amplitude of at least 10% of the average laser power density of the ring area can be varied. The average laser power density in the ring area can, in particular, be a maximum of 5% of the (total) laser power.

[0010] The variation amplitude can be either positive or negative. In other words, the average laser power density (of the core and / or ring region) can be periodically increased (with a positive variation amplitude) and / or reduced (with a negative variation amplitude).

[0011] This can lead to (additional) stabilization of the keyhole, particularly in workpieces with a lower viscosity, which reduces spatter and pores and allows the most consistent weld penetration depth to be achieved. The instabilities of the keyhole can be avoided or at least reduced in particular by increasing and reducing the steam rate and steam pressure quickly enough to prevent the keyhole from collapsing. In other words, the keyhole can be stabilized by specifically influencing the steam pressure (or the steam rate), which can lead to fewer spatter, pores and a constant weld penetration depth.

[0012] According to a further development of the laser device, the laser device can be configured to keep the average laser power density in the core region and / or the average laser power density in the ring region constant. With multiple laser beams or multiple laser spots, the average laser power density of at least one of the core regions and / or the average laser power density of at least one of the ring regions can be kept constant.

[0013] Alternatively or additionally, the average laser power density in the core region and / or the average laser power density in the ring region can be varied with the variation frequency. With multiple laser beams or multiple laser spots, the average laser power density of at least one of the core regions and / or the average laser power density of at least one of the ring regions can be varied with the variation frequency.

[0014] According to a further development of the laser device, the laser device can be configured to vary the average laser power density in the core region and the average laser power density in the ring region, each with a different variation frequency and / or a different variation amplitude. It is also conceivable that the average laser power densities in the core region and in the ring region can each be varied with the same variation frequency and / or variation amplitude.

[0015] This allows the laser spot to be specifically adjusted and optimized in specific areas, which enables further stabilization of the keyhole.

[0016] According to a further development of the laser device, the laser device can comprise at least one CW laser for generating the laser beam, in particular the core region and / or the ring region. The laser device can be set up such that the core region and / or the ring region of the laser spot are each modulated with a modulation frequency and a modulation amplitude. The modulation frequency can correspond to the variation frequency and the modulation amplitude can correspond to the variation amplitude. The CW laser can have an average power of at least 0.2 kW (kilowatts), preferably at least 4 kW.

[0017] In this way, the laser beam, in particular the core area and / or the ring area, can be generated using simple means.

[0018] It is also conceivable that the laser device for generating the laser beam, in particular the core region and / or the ring region, can comprise at least one pulsed laser. A pulse repetition rate of the pulsed laser can correspond to the variation frequency. The pulsed laser can have an average power of at least 0.2 kW, preferably at least 4 kW, and / or a pulse energy of at least 10 mJ (millijoules), preferably at least 50 mJ.

[0019] It is conceivable that the core region of the laser spot is generated by means of a pulsed laser (in particular an ns (nanosecond) pulsed laser) and the ring region of the laser spot is generated by means of a CW laser or vice versa.

[0020] The pulsed laser and / or the CW laser can each have a beam parameter product of a maximum of 8 mm*mrad (millimeters*milliradians). The pulsed laser and / or the CW laser can each be designed as a (multi-mode) NIR (Near Infrared) laser. It is also conceivable that the pulsed laser and / or the CW laser can each be designed as a laser in the visible range (VIS laser) with a wavelength in a blue or green wavelength range. The pulsed laser and / or the CW laser can each be designed as a solid-state laser.

[0021] The laser device may comprise a control device. The control device may be configured to program and / or control the (high-frequency) modulation or pulsation with the variation frequency and variation amplitude. The control device may be configured to control the core region and ring region of the laser spot generated by the light beam, in particular separately and independently of one another, or to modulate or adjust the respective average laser power density.

[0022] The laser device may include a nozzle for supplying a shielding gas (cutting or welding gas) to the workpiece. This nozzle may have a Laval internal geometry.

[0023] According to a further development of the laser device, the laser device can comprise at least two, in particular different, laser sources for generating the laser beam, in particular the core region and / or the ring region. For example, the core region can be generated by means of at least one first laser, and the ring region by means of at least one second laser.

[0024] This allows the laser spot to be generated and adjusted in specific areas, which enables further stabilization of the keyhole.

[0025] According to a further development of the laser device, the laser device for generating the laser beam and / or the laser spot can comprise a fiber (2 in 1 fiber) with a core region and a ring region. The core region of the fiber can have an outer diameter of at most 30 gm (micrometers), in particular of at most 20 gm, preferably of at most 10 gm (e.g. for fundamental mode or single mode). Alternatively, the core region of the fiber can have a larger outer diameter, in particular of at least 50 gm or 100 gm (e.g. for multi-mode). Alternatively or additionally, the ring region can have an outer diameter of 200 gm or 400 gm. The core region can be arranged within the ring region. The ratio between the outer diameter of the core region and the outer diameter of the ring region can be in the range from 1:2 to 1:9, in particular 1:3, 1:4 or 1:6.

[0026] The core region may have a cladding. The cladding may be arranged between the core region and the ring region. The cladding may have a maximum thickness of 10 μm. The cladding may have a lower refractive index than the core region and / or ring region. The fiber may be configured such that, due to the cladding of the core region, the light is "confined" within the core region, particularly due to total internal reflection at the interface between the core region and the cladding. Accordingly, the light in the ring region, which can be totally reflected between the cladding of the core region and an additional cladding of the ring region, may be "confined."

[0027] This allows for further stabilization of the weld area, especially the keyhole. This can further reduce instability (within the keyhole) and lead to fewer spatters and pores, as well as a consistent weld penetration. Due to the cladding of the core area and / or the annular area, light can be guided in an isolated manner in the core area and the annular area.

[0028] According to a further development of the laser device, the laser device can be configured such that at least two laser beams are generated and focused onto the workpiece. In particular, at least four laser beams can be generated and focused onto the workpiece. In particular, all of the laser beams can be of identical design. Accordingly, all of the laser spots generated on the workpiece by the respective laser beams can also be of identical design. To generate a plurality of laser beams, the laser device can comprise an optical element for beam splitting, in particular a wedge switch.

[0029] This allows the weld area, especially the keyhole, to be further stabilized. This can further reduce instability (within the keyhole) and lead to fewer spatters and pores, as well as a consistent weld penetration.

[0030] According to a further development of the laser device, the laser device can be configured such that a rise time and / or a fall time of the variation amplitude is a maximum of 10 ps (microseconds).

[0031] In this case, the rise time refers to the time required to increase the average laser power density to a maximum value (e.g., the positive variation amplitude). Similarly, the fall time refers to the time required to reduce the average laser power density to a minimum value (e.g., the negative variation amplitude).

[0032] According to a further development of the laser device, the laser device can comprise a scanner optics system for moving the laser beam over the workpiece. The scanner optics can have an imaging ratio in a range from 1:1 to 5:1, preferably from 1.9:1 or 3.4:1.

[0033] This allows the laser beam to be optimally focused on the workpiece and / or moved over the workpiece using simple means.

[0034] According to a further development of the laser device, the laser device can comprise an optical sensor for detecting the position of the laser beam and / or the workpiece. The optical sensor can be designed as a camera-based sensor or as a camera. It is also conceivable for the optical sensor to be designed as an interferometer-based sensor system. The laser beam and the optical sensor can be calibrated to one another.

[0035] This allows for simple position control of the laser beam and / or the workpiece. This allows for machining, particularly laser welding, of the workpiece to be carried out with the greatest possible precision.

[0036] The above object is further achieved by a method for machining at least one workpiece by means of at least one laser beam having the features of the subordinate

[0037] Claim solved. The processing may involve laser welding. The process comprises the following steps:

[0038] Providing the workpiece. The workpiece can be made of metal, in particular aluminum and / or copper. In the molten state (at melting temperature), the workpiece can have a viscosity of maximum 5 mPa*s (millipascals*second). The workpiece can have a thickness of maximum 4 mm (millimeters).

[0039] Generating and focusing at least one laser beam onto the workpiece such that the laser beam creates a laser spot on the workpiece, wherein the laser spot has a, in particular circular, core region and a, in particular annular, ring region. The average laser power density in the core region is higher than the average laser power density in the ring region.

[0040] Varying, in particular pulsing or modulating, the average laser power density in the core region and / or the average laser power density in the ring region, in each case with a variation frequency of at least 50 kHz and a variation amplitude of at least 10% of the respective average laser power density. The rise and / or fall time of the variation amplitude can be less than 10 ps (microseconds). The variation amplitude can be both positive and negative. In other words, the average laser power density can be periodically increased (with a positive variation amplitude) and / or reduced (with a negative variation amplitude). This can achieve (additional) stabilization of the keyhole, in particular in workpieces with a lower viscosity, whereby spatter and pores decrease and the most continuous welding depth possible can be achieved.Keyhole instabilities can be avoided or at least reduced by increasing and decreasing the steam rate and steam pressure quickly enough to prevent the keyhole from collapsing. In other words, the keyhole can be stabilized by selectively influencing the steam pressure (or steam rate), which can lead to fewer spatters, pores, and a consistent weld penetration.

[0041] The method may comprise the step of:

[0042] Supplying a protective gas (cutting or welding gas) to the workpiece, particularly in the area where the workpiece is being processed. This can be achieved using a nozzle, particularly one with a Laval internal geometry.

[0043] According to a further development of the method, the method may comprise the step:

[0044] Moving the laser beam and / or the workpiece in order to generate a feed of the laser beam focused on the workpiece. The laser beam can be moved over the workpiece using scanner optics. The movement of the laser beam and / or the workpiece can be a relative movement between the laser beam and the workpiece. In other words, either the laser beam or the workpiece or both can be moved. This allows continuous processing of the workpiece, e.g. a weld seam, to be generated using simple means.

[0045] According to a further development of the method, the method may comprise the step:

[0046] Determining the position of the laser beam and / or the workpiece. This can be achieved using an optical sensor.

[0047] Possible readjustment of a processing position of the laser beam and / or the workpiece.

[0048] This allows for simple position control and, in the event of a deviation, appropriate adjustment of the laser beam and / or the workpiece.

[0049] According to a further development of the method, the method may comprise the step:

[0050] Varying, in particular pulsing or modulating, the average laser power density in the core region and the average laser power density in the ring region, each with a different variation frequency and / or a different variation amplitude of the respective average laser power density.

[0051] This allows the respective energy input through the core region or the ring region to be targeted, adjusted, and optimized as desired. According to a further development of the method, a laser device as described above can be used to carry out the method.

[0052] With regard to the advantages that can be achieved, reference is made to the relevant explanations regarding the laser device. The measures described in connection with the laser device and / or those explained below can be used to further refine the method.

[0053] Further features, details and advantages of the invention will become apparent from the wording of the claims and from the following description of an embodiment with reference to the drawings. They show:

[0054] Fig. 1 is a schematic representation of a laser device for processing at least one workpiece;

[0055] Fig. 2 is a schematic plan view of the workpiece and a laser spot of a laser beam of the laser device according to Fig. 1;

[0056] Fig. 3 shows a schematic cross-section of a fiber of the laser device according to Figure 1;

[0057] Fig. 4 is a schematic diagram of a profile of average laser power densities in the core region and ring region of the laser spot of the laser beam of the laser device according to Figure 1.

[0058] In the following description and in the figures, corresponding components and elements bear the same reference symbols. For the sake of clarity, not all reference symbols are shown in all figures.

[0059] Figure 1 schematically shows a laser device 10 for processing at least one workpiece 12 using at least one laser beam 14. In this case, the processing involves laser welding.

[0060] The laser device 10 is configured to generate the laser beam 14 and to focus it on the workpiece 12 such that the laser beam 14 generates a laser spot 16 on the workpiece 12, wherein the laser spot 16 has a, in particular circular, core region 18 and a, in particular annular, ring region 20 (cf. Figure 2). An average laser power density 22 in the core region 18 is higher than an average laser power density 24 in the ring region 20 (cf. Figure 4).

[0061] The laser device 10 is also configured to vary the average laser power density 22 in the core region 18 and / or the average laser power density 24 in the ring region 20, each with a variation frequency of at least 50 kHz and a variation amplitude 26 of at least 10% of the respective average laser power density 22, 24 (cf. Figure 4).

[0062] The laser device 10 can be configured such that a rise time and / or a fall time of the variation amplitude 26 is a maximum of 10 ps.

[0063] The laser device 10 can be configured to vary the average laser power density 22 in the core region 18 and the average laser power density 24 in the ring region 20, each with a different variation frequency and / or a different variation amplitude 26.

[0064] The laser device 10 can comprise a CW laser for generating the laser beam 14, in particular the core region 18 and / or the ring region 20. The laser device 10 can be configured such that the core region 18 and / or the ring region 20 of the laser spot 16 is modulated with a modulation frequency and a modulation amplitude. The modulation frequency can correspond to the variation frequency, and the modulation amplitude can correspond to the variation amplitude 26. The CW laser can have an average power of at least 1 kW, in particular of at least 4 kW.

[0065] The laser device 10 in the present case comprises a scanner optics 34 for moving the laser beam 14 over the workpiece 12. The scanner optics 34 can have an imaging ratio in a range of 1:1 to 5:1, preferably 1.9:1 or 3.4:1.

[0066] The laser device 10 also comprises an optical sensor 36 for detecting the position of the laser beam 14 and / or the workpiece 12.

[0067] The laser device 10 can be configured such that at least two, in particular at least four, laser beams 14 are generated and focused onto the workpiece 12. All laser beams 14 (or the laser spots 16 generated by the respective laser beams 14) can be identically configured. Figure 2 shows a schematic plan view of the workpiece 12 and a laser spot 16 of the laser beam 14 of the laser device 10 according to Figure 1.

[0068] In the present case, the laser device 10 comprises a fiber 28 with a core region 30 and a ring region 32 for generating the laser beam 14 and / or the laser spot 16.

[0069] Figure 3 shows a schematic cross section of the fiber 28 of the laser device 10 according to Figure 1 .

[0070] The core region 30 of the fiber 28 is presently arranged within the ring region 32 of the fiber 28. The core region 30 of the fiber 28 can have an outer diameter of 50 pm or 100 pm. The ring region 32 of the fiber 28 can have an outer diameter of 200 pm or 400 pm.

[0071] In the present case, the laser device 10 has at least two laser sources for generating the laser beam 14. The laser sources can be designed differently. In the present case, light from a first laser source is coupled into the core region 30 of the fiber 28. For this purpose, the core region 30 of the fiber 28 can be coupled to a first optical fiber 38 (first fiber). The first optical fiber 38 coupled to the core region 30 is indicated in Figure 3 by a dashed circle.

[0072] In the present case, light from at least one second laser source is coupled into the ring region 32 of the fiber 28. For this purpose, the ring region 32 of the fiber 28 can be coupled to a plurality of, in this case six, second light guides (second fibers). The second light guides 40 coupled to the ring region 32 of the fiber 28 are each indicated in Figure 3 by means of a dashed circle. The six second light guides 40 can be supplied with light by means of a common second laser source. It is also conceivable that the six second light guides 40 can each be supplied with light by means of a separate second laser source (i.e. a total of six second laser sources).

[0073] Figure 4 shows a schematic diagram of a profile of the average laser power densities 22, 24 in the core region 18 and ring region 20 of the laser spot 16 of the light beam 14 of the laser device 10 according to Figure 1.

[0074] In the diagram shown, an average laser power density 42 of the laser spot 16 of the laser beam 14 of the laser device 10 is shown in W / cm 2 (Watts per square centimeter) is plotted against time 44 in seconds. In other words, the x-axis represents time 44 in seconds and the y-axis represents the average laser power density 42 in W / cm 2 shown .

[0075] In the present case, the average laser power density 22 of the core region 18 of the laser spot 16 is kept constant. In other words, the average laser power density 22 of the core region 18 of the laser spot 16 is not modulated in the present case. The average laser power density 24 of the ring region 20 is modulated in the present case with the modulation frequency and the modulation amplitude. In other words, the average laser power density 24 of the ring region 20 is periodically varied by at least 10% (modulation amplitude). Thus, the average laser power density 24 of the ring region 20 of the laser spot 16 is changed by the modulation amplitude or the variation amplitude 26 at regular intervals of a maximum of 20 ps (since the modulation frequency or variation frequency is at least 50 kHz).In the example shown, the average laser power density 24 of the ring region 20 is reduced by the variation amplitude 26 at intervals of a maximum of 20 ps and then increased back to the initial value. In this case, the variation amplitude is greater than 10% and less than 100% of the average laser power density 24 of the ring region 20 of the laser spot 16.

[0076] In the following, a method for processing, in particular laser welding, at least one workpiece 12 is described with reference to Figures 1 to 4. The method comprises the following steps:

[0077] Providing the workpiece 12. The workpiece 12 can be made of metal, in particular aluminum and / or copper. The workpiece 12 can have a viscosity of a maximum of 5 mPa*s in the molten state.

[0078] Generating and focusing at least one laser beam 14 onto the workpiece 12 such that the laser beam 14 generates a laser spot 16 on the workpiece 12, wherein the laser spot 16 has a, in particular circular, core region 18 and a, in particular annular, ring region 20. An average laser power density 22 in the core region 18 is higher than an average laser power density 24 in the ring region 20.

[0079] Varying, in particular pulsing or modulating, the average laser power density 22 in the core region 18 and / or the average laser power density 24 in the ring region 20, each with a variation frequency of at least 50 kHz and a variation amplitude 26 of at least 10% of the respective average laser power density 22, 24. A rise and / or fall time of the variation amplitude 26 can be less than 10 ps.

[0080] The method may comprise the step of:

[0081] Moving the laser beam 14 and / or the workpiece 12 to generate a feed of the laser beam 14 or laser spot 16 focused on the workpiece 12. The movement of the laser beam 14 or the laser spot 16 can be implemented by means of a scanner optics 34.

[0082] The method may further comprise the step of:

[0083] Determining the position of the laser beam 14 and / or the workpiece 12. This can be implemented using an optical sensor 36.

[0084] The method may comprise the step of:

[0085] Varying, in particular pulsing or modulating, the average laser power density 22 in the core region 18 and the average laser power density 24 in the ring region 20, each with a different variation frequency and / or a different variation amplitude 26 of the respective average laser power density 22, 24.

[0086] To carry out the method, a laser device 10 according to the above embodiments, in particular the laser device 10 shown in Figure 1, can be used.

Claims

Patent claims Laser device (10) for processing, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14), wherein the laser device (10) is configured to generate the laser beam (14) and to focus it on the workpiece (12) in such a way that the laser beam (14) generates a laser spot (16) on the workpiece (12), wherein the laser spot (16) has a, in particular circular, core region (18) and a, in particular annular, ring region (20), wherein an average laser power density (22) in the core region (18) is higher than an average laser power density (24) in the ring region (20), wherein the laser device (10) is additionally configured to vary the average laser power density (22) in the core region (18) and / or the average laser power density (24) in the ring region (20) with a variation frequency of at least 50 kHz and a Variation amplitude (26) of at least 10% of the respective average laser power density (22,24) to vary ., 2. Laser device (10) according to claim 1, characterized in that the laser device (10) is configured to vary the average laser power density (22) in the core region (18) and the average laser power density (24) in the ring region (20) each with a different variation frequency and / or a different variation amplitude (26).

3. Laser device (10) according to claim 1, characterized in that the laser device (10) is designed to keep the average laser power density (22) in the core region (18) and / or the average laser power density (24) in the ring region (20) constant.

4. Laser device according to one of the preceding claims, characterized in that the laser device (10) for generating the laser beam (14), in particular the core region (18) and / or the ring region (20), comprises at least one CW laser, wherein the laser device (10) is set up such that the core region (18) and / or the ring region (20) of the laser spot (16) is each modulated with a modulation frequency and a modulation amplitude, wherein the modulation frequency corresponds to the variation frequency and the modulation amplitude corresponds to the variation amplitude (26), in particular wherein the CW laser has an average power of at least 0.2 kW, preferably at least 4 kW.

5. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) comprises at least two, in particular different, laser sources for generating the laser beam (14), in particular the core region (18) and / or the ring region (20).

6. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) for generating the laser beam (14) and / or the laser spot (16) comprises a fiber (28) with a core region (30) and a ring region (32).

7. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) is set up such that at least two, in particular at least four, laser beams (14) are generated and focused onto the workpiece (12), in particular wherein all laser beams (14) and / or laser spots (16) are each identically designed.

8. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) is arranged such that a rise and / or fall time of the variation amplitude (26) is a maximum of 10 ps.

9. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) comprises a scanner optics (34) for moving the laser beam (14) over the workpiece (12), in particular wherein the scanner optics (34) has an imaging ratio in a range of 1:1 to 5:1, preferably of 1.9:1 or 3.4:

1.

10. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) comprises an optical sensor (36) for detecting the position of the laser beam (14) and / or the workpiece (12).

11. Method for processing, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14) comprising the steps: Providing the workpiece (12), in particular wherein the workpiece (12) is made of metal, preferably aluminum and / or copper, and has a viscosity of at most 5 mPa*s in the molten state; Generating and focusing at least one laser beam (14) onto the workpiece (12) in such a way that the laser beam (14) generates a laser spot (16) on the workpiece (12), wherein the laser spot (16) has a, in particular circular, core region (18) and a, in particular annular, ring region (20), wherein an average laser power density (22) in the core region (18) is higher than an average laser power density (24) in the ring region (20); Varying, in particular pulsing or modulating, the average laser power density (22) in the core region (18) and / or the average laser power density (24) in the ring region (20), each with a variation frequency of at least 50 kHz and a variation amplitude (26) of at least 10% of the respective average laser power density (22, 24), in particular wherein a rise and / or fall time of the variation amplitude (26) is a maximum of 10 ps.

12. The method according to claim 11, characterized in that the method comprises the step: Moving the laser beam (14) and / or the workpiece (12) to achieve a feed of the workpiece (12) focused laser beam (14), in particular by means of a scanner optics (34).

13. The method according to claim 11 or 12, characterized in that the method comprises the step: Determining a position of the laser beam (14) and / or the workpiece (12), in particular by means of an optical sensor (36) and Possible readjustment of a processing position of the laser beam (14) and / or the workpiece (12).

14. Method according to one of claims 11 to 13, characterized in that the method comprises the step: Varying, in particular pulsing or modulating, the average laser power density (22) in the core region (18) and the average laser power density (24) in the ring region (20), each with a different variation frequency and / or a different variation amplitude (26) of the respective average laser power density (22, 24).

15. Method according to one of claims 11 to 14, characterized in that a laser device (10) according to one of claims 1 to 10 is used to carry out the method.

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