LASER MATERIAL PROCESSING ORDER

Description

Technical application area

[0001] The present invention relates to an arrangement for laser material processing according to the preamble of claim 1 (see, for example, US 2006 / 213885 A1).

[0002] Lasers are used in many technical fields for material processing, for example, for surface structuring, joining, cutting, or in additive manufacturing. The laser beam sources available for laser material processing, especially those for ultrashort pulsed laser radiation, are being provided with ever-increasing power levels. However, the maximum power for a laser spot on the workpiece is limited by the material properties. To efficiently utilize the high laser power, the total power is therefore often divided into several partial beams. Furthermore, rapid material processing can be achieved by arranging the laser spots in a two-dimensional matrix of multiple rows and columns. To maintain flexibility in the processing process, this requires the ability to switch each individual partial beam on and off separately.Acousto-optic modulators (AOMs) are frequently used for this purpose. The switching speed and diffraction efficiency of the beam deflection in acousto-optic modulators are strongly dependent on the beam diameter, the angle of incidence of the beam on the crystal of the acousto-optic modulator, and the beam divergence. Therefore, the beam diameter should be kept as small as possible. The lower limit of the beam diameter is determined by the damage threshold of the acousto-optic modulator. State of the art

[0003] From S. Bruening et al., "Ultra-fast multi-spot parallel processing of functional micro- and nano scale structures on embossing dies with ultrafast lasers," presented at the Lasers in Manufacturing Conference 2017, a laser arrangement for laser material processing is known in which a collimated laser beam from a laser beam source is split into several partial beams by a beam splitting device. These partial beams are then aligned parallel to each other via a Fourier lens and guided through a multi-channel acousto-optic modulator. The beam splitting occurs only in one plane, so that a one-dimensional spot matrix is ​​generated in the processing plane. The acousto-optic modulator is located in the intermediate focus of the relay optics built with the Fourier lens.With such an arrangement, two-dimensional spot matrices can be generated in the processing plane using appropriately designed beam splitting devices and several multi-channel acousto-optic modulators. Multi-channel acousto-optic modulators can deflect several partial beams propagating in one plane independently of each other. Therefore, several multi-channel modulators are necessary for two-dimensional beam matrices. Due to the design, however, the optics in front of the modulators become very wide, necessitating large, and usually very expensive, lenses for beam shaping. Furthermore, in the above solution, the partial beams exhibit divergence in the acousto-optic modulator due to the intermediate focus, where the beam diameter in the center of the modulator is smaller than at the entry and exit planes of the crystal. This reduces the diffraction efficiency and increases the switching time of the acousto-optic modulator.

[0004] The object of the present invention is to provide an arrangement for laser material processing with a two-dimensional beam matrix that enables efficient modulation of the individual beams and can be implemented in a more compact form. Description of the invention

[0005] The problem is solved by the arrangement for laser material processing according to claim 1. Advantageous embodiments of the arrangement are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

[0006] The proposed arrangement for laser material processing comprises at least one laser beam source emitting a collimated laser beam, a beam splitting device, a first optical arrangement, a modulation device, and a dynamic beam deflection device. The laser beam source can, for example, be a laser with collimation optics positioned upstream. Of course, a laser that already emits a collimated laser beam can also be used. The beam splitting device is designed to split the collimated laser beam two-dimensionally, i.e., in two mutually perpendicular directions (hereinafter also referred to as the x and y directions), into several partial beams that are not parallel to each other in at least one first dimension.Preferably, at least four non-parallel partial beams, i.e., at least a 4xN beam matrix (with N ≥ 2), are generated in the first dimension. The first optical arrangement is designed and positioned such that it aligns the partial beams parallel to each other in the first dimension without affecting the collimation of the individual partial beams. The modulation device following the first optical arrangement comprises several acousto-optic modulators, which are multi-channel in the first dimension and with which the individual partial beams can be modulated independently of one another. With the dynamic beam deflection device, e.g., a 2D galvanometer scanner, the partial beams are then dynamically deflected in two perpendicular directions and guided over a processing plane.A focusing optic, such as an F-theta lens, is typically arranged between the dynamic beam deflection device and the processing plane to focus the partial beams onto the processing plane. By modulating the partial beams in the acousto-optic modulators, the individual laser spots in the processing plane can be switched on and off independently. The proposed arrangement is characterized by the fact that the first optical arrangement comprises several prisms designed and arranged such that, as the partial beams pass through the prisms, they align them parallel to each other in the first dimension by means of double refraction (at the entrance and exit surfaces of the prism). This alignment of the partial beams thus occurs not by reflection at a prism surface, but solely through double refraction.Each partial beam, whose propagation direction must be adjusted for parallel alignment, is assigned one of the prisms. Preferably, a single prism is used for all partial beams of a beam plane that is perpendicular to the first dimension. For example, in the case of an 8x8 beam matrix, each prism deflects all 8 partial beams of such a beam plane simultaneously. In this case, a total of 8 prisms are required for 64 partial beams.

[0007] By using prisms for beam parallelization in the first dimension, which corresponds to the x-direction, the collimation of the individual partial beams is maintained, so that these partial beams no longer exhibit divergence in the acousto-optic modulators. In this way, maximum switching efficiency can be achieved in the acousto-optic modulators, and the maximum possible power per partial beam can be transmitted to the processing plane. Furthermore, using prisms for beam parallelization allows for a more compact arrangement than when using relay optics. The prisms are preferably designed so that they can be glued or joined together to form a prism stack without additional components. In particular, the prisms have a trapezoidal base with parallel top and bottom surfaces, which are in turn parallel to the optical axis.

[0008] In an advantageous embodiment, the prisms are rigidly connected to one another to form a prism stack, for example by gluing or joining. This significantly simplifies the adjustment of the arrangement due to a reduction in the prism degrees of freedom. Preferably, the first optical arrangement additionally includes an afocal telescope by which the beam diameter of the partial beams is adjusted, and in particular reduced, to the dimension required (and still permissible) in the acousto-optic modulators. The afocal telescope is also used to further separate the partial beams that diverge after the beam splitting device (but remain collimated) (the divergence angle is directly related to the reduction factor of the telescope). The beam splitting device can, for example, be formed by at least one diffractive optical element (DOE), as is known from the prior art.

[0009] By parallelizing the partial beams in the first dimension (x-direction), they converge parallel to each other at the respective (in this dimension) multi-channel acousto-optic modulator, whose crystal entrance surface (by rotation about the x-axis) is positioned at the Bragg angle to the incoming partial beams. In the second dimension, perpendicular to this and subsequently corresponding to the y-direction, the partial beams are not parallelized. A multi-channel acousto-optic modulator is used for each beam plane with partial beams parallelized in the first dimension. By employing several beam deflection elements, particularly mirrors, between the beam splitting device and the dynamic beam deflection device, a folded beam path can be generated, enabling an even more compact design of the arrangement. The beam deflection preferably occurs in planes perpendicular to the x-direction.

[0010] The dynamic beam deflection device preferably has two mirrors that can be pivoted about axes perpendicular to each other, for example in the form of a two-dimensional galvanometer scanner.

[0011] In an advantageous embodiment, a second optical arrangement is positioned between the modulation device and the dynamic beam deflection device. This arrangement deflects the partial beams exiting the modulation device in such a way that the spacing between the partial beams in the processing plane is reduced or increased compared to an embodiment without this second optical arrangement. In this way, the desired spot spacing in the processing plane can be adjusted. Furthermore, this second optical arrangement can also be used for prefocusing or to change the beam diameter of the collimated partial beams. Preferably, the second optical arrangement incorporates a telescope with an input and an output optic, between which several prisms are arranged. These prisms correspondingly reduce or increase the spacing between the partial beams in the processing plane.These prisms are also preferably rigidly connected to each other, forming a prism stack. In particular, the prisms have a trapezoidal base with parallel top and bottom surfaces, which are parallel to the optical axis. The deflection of the individual partial beams, as in the first optical arrangement, is achieved by double refraction as they pass through the respective prism. This makes it possible to select the spot spacing and spot size in the machining plane or on the workpiece independently of the channel spacing of the respective multi-channel acousto-optic modulator. The spot size is set by the dimensions of the telescope, and the spot spacing by the dimensions of the prisms.

[0012] The proposed arrangement for laser material processing enables the efficient use of high laser power (> 1 kW), e.g., in the ultrashort pulse range, while simultaneously reducing the size of necessary optical elements and the required installation space. Due to the scalability and flexibility of the arrangement, its industrial applications lie primarily in surface structuring. This includes the creation of functional surfaces for friction reduction, for example, on aircraft wings, or the production of printing rollers. Since the scalability of the arrangement allows more laser power to be delivered to the workpiece via a larger spot matrix (greater number of laser spots), the productivity of laser material processing applications is significantly increased. Brief description of the drawings

[0013] The proposed arrangement is explained in more detail below using exemplary embodiments in conjunction with the drawings. These show: Fig. 1 a schematic representation of a spot matrix in a processing plane (a) and, by way of example, during the processing of a workpiece (b); Fig. 2 a schematic representation of the passage of a divergent beam through an AOM (a) and a representation of the beam waist of a beam within an AOM (b); Fig. 3 a side view (a) of a prior art laser material processing arrangement and a top view (b) of this arrangement; Fig. 4 a side view (a) of an exemplary embodiment of the proposed laser material processing arrangement and a top view (b) of this arrangement; Fig. 5 a side view of the beam path through the prisms in an arrangement according to Figure 4; Fig. 6 an example of an embodiment of the proposed arrangement with folded beam paths in a top view as in Figure 4b ; Fig. 7 a side view of an exemplary embodiment of the second optical arrangement of the proposed arrangement; and Fig. 8 an exemplary embodiment in which the beam path through the dynamic beam deflection device of the proposed arrangement is shown. Ways to implement the invention

[0014] To efficiently utilize the total power of currently available laser beam sources, the emitted laser beam is often split into several partial beams 1, which then create a two-dimensional arrangement of laser spots in the form of a matrix on the workpiece 2. Figure 1aThis is illustrated by an example of a two-dimensional spot matrix consisting of the individual partial beams 1 in the processing plane. Each hatching represents the partial beams that can be individually switched on using a multi-channel acousto-optical modulator (AOM). Figure 1b An example of machining a workpiece 2 is shown, in which each row or line of the matrix (each a hatch) processes a plane of the workpiece 2. The entire matrix is ​​deflected in x and y within the distance between the individual partial beams. In order to be able to machine arbitrary structures, each individual partial beam 1 must be able to be switched on and off separately. However, with the acousto-optical modulators used for this purpose, the switching speed and diffraction efficiency of the beam deflection depend strongly on the beam diameter, the angle of incidence between the beam and the AOM, and the divergence of the beam.

[0015] Figure 2aFigure 1 shows a divergent input beam 3 that strikes an acousto-optic modulator 4 at the Bragg angle and can be switched between zeroth and first order by this modulator. With a divergent input beam, the edge beams deviate from the Bragg angle, thereby reducing the proportion of deflected power. When using relay optics according to the prior art, with which the partial beams are guided into the acousto-optic modulators, the beam diameter in the center of the acousto-optic modulator 4 is smaller than at the edges, as can be seen from beam 3 of the figure. Figure 2bAs indicated, the switching speed between the zeroth and first orders depends on the beam diameter. The minimum beam diameter is determined by the destruction threshold of the AOM crystal. Due to the divergent beam formation in the acousto-optic modulator, either the switching speed is increased while remaining within the destruction threshold, or the destruction threshold is exceeded while the switching speed remains constant.

[0016] Figure 3Figure 1 shows a state-of-the-art embodiment of a laser arrangement for laser material processing, in which a relay optic 7 with corresponding lenses is used for parallelizing the partial beams 1. The laser beam 10 emanating from the beam source 5 is split into several partial beams two-dimensionally (x and y directions) by the beam splitting device 6. The partial beams 1 are parallelized by a first relay optic 7 and guided through multi-channel acousto-optic modulators 4. These partial beams 1 are then appropriately combined by a second relay optic 8 and directed into the processing plane by a 2D scanner 9 and guided across the processing plane. Figure 3a This shows a side view of the arrangement with the multi-channel acousto-optic modulator 4 in this first dimension (x-direction). Figure 4bThe top view of this arrangement shows the corresponding multiple acousto-optical modulators 4.

[0017] In contrast, the proposed arrangement does not use relay optics to parallelize the partial beams 1 in front of the acousto-optic modulators 4. Figure 4a This shows a side view, Figure 4b A top view of an example of the proposed arrangement. While the design of the... Figure 3 While the lenses of the relay optics 7 must have a diameter equal to the total width of the assembly, this is no longer the case with the proposed arrangement. The parallelization in one of the two dimensions (x and y directions), into which the individual partial beams 1 are divided by the beam splitting device 6, is achieved in this example by using a prism stack 11, as shown in the side view of the arrangement in Figure 4aThis is schematically indicated. Each prism 12 deflects all rays of a ray plane that is perpendicular to the xz-plane. All prisms 12 are assembled to form an optical component, the prism stack 11, as shown in Figure 4a This is indicated. This prism stack 11 ensures that the necessary collimation of the partial beams in the acousto-optic modulators 4 is maintained during parallelization.

[0018] Starting from the beam source 5, the collimated raw beam 10 is split into a two-dimensional beam matrix using the beam-splitting element of the beam splitting device 6. To reduce the beam diameter, an afocal telescope 13 is used, which reduces the size of all beams simultaneously. The beams emerge from the first telescope 13 collimated, but divergent in both directions of the matrix extent, i.e., not parallel to each other. For complete beam separation, the beam matrix is ​​propagated freely through space. Each beam plane of the beam matrix is ​​followed by an individual prism 12 of the prism stack 11, which deflects the beams of this plane so that they enter the acousto-optic modulators 4 perpendicular to the entry plane. This is shown schematically in Figure 5 indicated, which shows a side view of the arrangement with the prism stack 11 and a multi-channel acousto-optic modulator 4.

[0019] While the prism stack 11 parallelizes all partial beams 1 of the first dimension (x-direction), the partial beams in the second dimension (y-direction) continue to diverge in the direction of the acousto-optic modulators 4, as shown in Figure 4b As indicated. The individual acousto-optic modulators 4 can be suitably aligned and arranged in this second dimension to obtain the optimal angle of incidence of the partial beams 1 on the crystals of the acousto-optic modulators 4 in this dimension.

[0020] The acousto-optical modulators 4 can also be rotated by 90°, perpendicular to the propagation axis (dashed-dotted line of the Fig. 6 ) are arranged to reduce the overall length of the optics of the arrangement by folding the beam path. The beam redirection of the partial beams 1 is then achieved by suitably arranged deflecting elements, e.g. deflecting mirrors 16, as shown in Figure 6The proposed arrangement is shown in an exemplary top view.

[0021] After passing through the acousto-optic modulators 4, the partial beams 1 are again appropriately adjusted in their beam diameter by a second telescope 15, preferably enlarged, in order to achieve the smallest possible focus in the processing plane by means of a focusing optics arranged after the 2D scanner 9. The focusing optics are in Figure 4 not shown. Furthermore, a second prism stack 14 is also used to be able to adjust the distance of the individual laser spots in the processing plane independently of the second telescope 15.

[0022] This combination of a second telescope 15 and a second prism stack 14 makes it possible to reconcile the opposing conditions of spot diameter and spot spacing on the workpiece or in the machining plane with the beam diameter and beam spacing in the acousto-optic modulators. The prism stack 14 can be advantageously integrated into the second telescope 15. This telescope 15 has, in a known manner, an input optic 17 and an output optic 18, with the second prism stack 14 integrated between the input and output optics. The second prism stack 14 and the second telescope 15 must be appropriately matched for this purpose. The integration of this second prism stack 14 creates the additional degree of freedom to adjust the spot spacing in the machining plane independently of the beam diameter. Figure 7Figure 1 shows a corresponding side view of this arrangement. The partial beams 1 emerge collimated and parallel from the acousto-optic modulators. By integrating the prism stack 14 within this second telescope 15, the spot diameter can be adjusted independently of each other via the dimensions of the input and output optics 17, 18 (and their spacing), and the spot spacing can be adjusted independently of each other via the dimensions of the prism stack 14.

[0023] Behind this second telescope 15, the two-dimensional scanner 9 deflects the entire beam matrix, as already described in Figure 4 is indicated schematically. Figure 8 Figure 1 shows a more detailed view of this 2D galvanometer scanner 9, which is formed in a known manner from two mirrors pivotable about axes perpendicular to each other, hereinafter referred to as X' scanner 20 and Y' scanner 21. Figure 8 This is a side view ( Figure 8a ), a top view ( Figure 8b) and a front view ( Figure 8c ) this scanner is shown schematically. Between the scanner 9 and the processing plane, a lens (focusing optic 19) focuses the partial beams 1 onto the processing plane or onto the workpiece. In the present embodiment, the second telescope 15 is dimensioned such that the intersection point 22 of all partial beams 1 lies between the two deflection mirrors, i.e., between the X' scanner 20 and the Y' scanner 21. This intersection point 22 is in Figure 8 This design avoids image errors in the processing plane caused by beam deflection. Reference symbol list

[0024] 1 Partial beams 2 Workpiece 3 Divergent input beam 4 Acousto-optic modulator (AOM) 5 Beam source 6 Beam splitting device 7 Relay optics before AOM 8 Relay optics after AOM 9 2D scanner 10 Collimated laser beam 11 First prism stack 12 Prism 13 First telescope 14 Second prism stack 15 Second telescope 16 Deflection mirror 17 Input optics 18 Output optics 19 Focusing optics 20 X' scanner 21 Y' scanner 22 Beam intersection point

Claims

1. Laser material machining assembly, having - a laser beam source (5), which emits a collimated laser beam (10), - a beam splitter (6), which splits the collimated laser beam (10) into multiple sub-beams (1), - a dynamic beam deflection device (9), with which the sub-beams (1) are dynamically deflectable into two directions aligned perpendicularly to each other and can be guided over a machining plane, characterized in that: the beam splitter (6) is configured such that the multiple sub-beams (1) run non-parallel to each other at least in a first dimension, and that the assembly further comprises - a first optical assembly, which aligns the sub-beams (1) in the first dimension parallel to each other, - a modulating device with a plurality of acousto-optical modulators (4), which are of multichannel design in the first dimension and with which the individual sub-beams (1) can be modulated independently of each other, - wherein the first optical assembly has several first prisms (12), which are designed and arranged such that the sub-beams (1) are aligned in parallel to each other in the first dimension upon passing through the first prisms (12) by means of a double diffraction in each case.

2. Assembly according to Claim 1, characterized in that the first prisms (12) are connected rigidly to each other to form a first prism stack (11).

3. Assembly according to Claim 1 or 2, characterized in that the first optical assembly also includes a first, preferably afocal telescope (13), by which a beam diameter of the sub-beams (1) is reduced.

4. Assembly according to any one of Claims 1 to 3, characterized in that the dynamic beam deflection device (9) includes two mirrors (20, 21), which can be swivelled about axes that are aligned perpendicular to one another.

5. Assembly according to any one of Claims 1 to 4, characterized in that a second optical assembly is arranged between the modulating device and the dynamic beam deflection device (9), which second assembly deflects the sub-beams (1) exiting the modulating device in such manner that a mutual distance between the sub-beams (1) in the machining plane is reduced or enlarged.

6. Assembly according to Claim 5 in conjunction with Claim 4, characterized in that the second optical assembly is designed such that the sub-beams (1) intersect between the two swivelling mirrors (20, 21) of the dynamic beam deflection device (9).

7. Assembly according to Claim 5 or 6, characterized in that the second optical assembly includes a second telescope (15) with an input optic (17) and an output optic (18), wherein the second telescope (15) includes an assembly of a plurality of second prisms (12) between the input and the output optics (17, 18), by which the mutual distance between the sub-beams (1) in the machining plane is reduced or enlarged.

8. Assembly according to Claim 7, characterized in that the second prisms (12) are rigidly connected to each other, forming a second prism stack (14).

9. Assembly according to any one of Claims 1 to 8, characterized in that the beam splitter (6) is formed by at least one diffractive optical element.

10. Assembly according to any one of Claims 1 to 9, characterized in that the acousto-optical modulators (4) are aligned such that the sub-beams (1) of each beam plane in which the sub-beams (1) are aligned parallel to each other are perpendicularly incident on the acousto-optical modulators (4).

11. Assembly according to any one of Claims 1 to 10, characterized in that sub-beams (1) are guided between the beam splitter (6) and the dynamic beam deflection device (9) via multiple deflecting elements (16) to reduce the installation space for the assembly through a reticulated beam path.