Device for homogenizing laser light and arrangement of a plurality of such devices

Abstract

Device (1.1-1.m) for homogenizing laser light (2.1-2.m), comprising - a first microlens array (3) with a plurality of microlenses (30.1-30.n) arranged side by side in a first direction, - a second microlens array (4) with a plurality of microlenses (40.1-40.n) arranged side by side in the first direction, wherein the second microlens array (4) is arranged at a distance from the first microlens array (3) in the direction of propagation of the laser light (2.1-2.m) and the plane (41) of the lens vertex of the second microlens array (4) is angled at an angle |α| to the plane (31) of the lens vertex of the first microlens array (3). is inclined and wherein the microlens arrays (3, 4) are configured such that the focal lengths of the microlenses (30.1-30.n, 40.1-40.n) arranged next to each other in the first direction change from the first microlens (30.1, 40.1) to the nth microlens (30n, 40n), characterized in that an optical wedge (5) is arranged behind the second microlens array (4) in the direction of beam propagation and the focal lengths of the microlenses (30.1-30.n, 40.1-40.n) of the microlens arrays (3, 4) are selected such that a focal plane (6) of the device (1.1-1.m) lies in an air gap (7) between the second microlens array (4) and the optical wedge (5).

Description

[0001] The present invention relates to a device for homogenizing laser light, comprising a first microlens array with a plurality of microlenses arranged side by side in a first direction, a second microlens array with a plurality of microlenses arranged side by side in the first direction, wherein the second microlens array is spaced apart from the first microlens array in the direction of laser light propagation, and the plane of the lens vertices of the second microlens array is inclined to the plane of the lens vertices of the first microlens array by an angle |α|, and wherein the microlens arrays are configured such that the focal lengths of the microlenses arranged side by side in the first direction change from the first microlens to the nth microlens. Furthermore, the present invention relates to an arrangement of a plurality of such devices for homogenizing laser light.

[0002] From WO 2008 / 043491 A2, a device for homogenizing laser light is known, which is monolithically constructed. The device has two spaced-apart microlens arrays, wherein the plane of the lens vertices of the second microlens array is inclined at an angle α relative to the plane of the lens vertices of the first microlens array. The microlenses of the two microlens arrays are arranged according to their diameters or focal lengths. Starting from a first microlens of the first microlens array and a first microlens of the second microlens array, the distance between which is the shortest distance between all corresponding microlenses of the two microlens arrays, the diameters or focal lengths increase in a first direction in which the microlenses are arranged side by side.This means that the last microlens of the first microlens array and the last microlens of the second microlens array have the largest diameter or focal length and the greatest distance from each other, respectively. Devices for homogenizing laser beams are also known from CN 103926804 A, US 2018 / 0017717 A1, and DE 10 2008 017 947 A1.

[0003] A disadvantage of this device for homogenizing laser light is that the focal points of the microlenses of the first microlens array lie on the surface of the microlenses of the second microlens array or within the glass substrate of the second microlens array. This means that, depending on the operating parameters of the laser light source, particularly the intensity, the illumination of the second microlens array, and the beam divergence, energy densities of the laser light can very quickly occur that can lead to the destruction threshold of a coating on the microlenses of the second microlens array or the destruction threshold of the glass substrate of the second microlens array being reached.This can lead to irreversible destruction of the second microlens array when using high-energy laser radiation, such as that used in material processing, especially for the crystallization of silicon.

[0004] Furthermore, the prior art device for homogenizing laser light suffers from the problem that, with increasing inclination angle α of the plane of the lens vertex of the second microlens array, a physical scanning effect occurs, depending on the type of illumination, which is typically Gaussian. This leads to an undesirable, essentially linear increase or decrease in the intensity profile along the resulting linear intensity distribution in the working plane. Such macro-inhomogeneity causes the workpiece to be processed unevenly, which should be avoided at all costs.

[0005] Furthermore, the monolithic design of the device for homogenizing laser light known from WO 2008 / 043491 A2 does not allow for subsequent adjustment, in particular adjustment of the distance for fine-tuning the line length in the working plane.

[0006] The present invention aims to provide a device for homogenizing laser light of the type mentioned above and an arrangement of a plurality of such devices which, during operation in a laser device, lead to a lower energy density in and on the optical components and can effectively reduce micro- or macro-inhomogeneities.

[0007] The solution to this problem is provided by a device for homogenizing laser light of the type mentioned above, having the features of the characterizing part of claim 1. With regard to the arrangement, this problem is solved by an arrangement having the features of claim 10. The dependent claims relate to advantageous embodiments of the invention.

[0008] An inventive device for homogenizing laser light is characterized in that an optical wedge is arranged behind the second microlens array in the beam propagation direction, and the focal lengths of the microlenses of the microlens arrays are selected such that a focal plane of the device lies in an air gap between the second microlens array and the optical wedge. The first and second microlens arrays of the inventive, non-monolithic device for homogenizing laser light have varying radii of curvature, diameters, and focal lengths, respectively, in the first direction, so that interference-induced micro-inhomogeneities can be effectively suppressed.Because the focal plane of the device is located in an air gap behind the second microlens array and in front of the optical wedge in the direction of laser light propagation, the device presented here for homogenizing laser light is also suitable for applications involving very high laser powers, especially very high pulse energies. This is because high energy input into the optical components of the device, particularly into the glass substrate of the second microlens array or a coating of the second microlens array, can be effectively prevented. Since the focal plane is located within the air gap between the second microlens array and the optical wedge, excessive energy input into the optical wedge can also be effectively prevented. Furthermore, due to the non-monolithic design of the device, the first and second microlens arrays are two physically separate components.This makes it advantageously possible to compensate for decentering errors between the microlens arrays and also to change the distance between the microlens arrays. In particular, this change in distance allows the resulting line length in a working plane to be varied within a certain range.

[0009] In an advantageous embodiment, the microlens arrays are designed such that the focal lengths of the microlenses arranged side by side in the first direction increase successively from the first microlens to the nth microlens. Such a design particularly facilitates the simpler fabrication of the microlens arrays.

[0010] In a preferred embodiment, it is proposed that the number of microlenses in the first microlens array corresponds to the number of microlenses in the second microlens array, such that each microlens in the second microlens array is associated with a microlens in the first microlens array. This results in the partial beams of laser light that pass through an i-th microlens (i = 1...n) of the first microlens array, at least for the most part, also passing through an i-th microlens (i = 1...n) of the second microlens array, thus ensuring an association of the microlenses.

[0011] In a particularly preferred embodiment, it is proposed that the microlenses are designed as cylindrical lenses whose cylindrical axes are oriented in a second direction perpendicular to the first direction and perpendicular to a third direction, which defines the beam propagation direction of the laser light. The cylindrical axes of the lenses are thus oriented parallel to each other. For example, acylindrical microlenses (e.g., for the second microlens array) or spherical microlenses can also be used, although the complexity of the overall optical setup increases further, particularly with a spherical design. The use of cylindrical lenses is therefore more advantageous in practical applications.

[0012] In a preferred embodiment, the optical wedge may have a light-entry surface oriented parallel to the plane of the lens vertices of the second microlens array. This results in the light-entry surface of the optical wedge also being inclined at an angle |α| to the plane of the lens vertices of the first microlens array. Consequently, the angular displacement caused by the second microlens array is compensated by the optical wedge, resulting in only a parallel displacement.

[0013] The well-defined common focal plane within the air gap between the second microlens array and the optical wedge, which is located at a distance d LThe arrangement behind the second microlens array can be achieved in particular by adjusting the radii of curvature or focal lengths of the microlenses of the first microlens array. Preferably, the focal length f1 (i) the i-th microlens of the first microlens array: f1(i)=−(f(i))2dGnG+dL−f(i) where d G the glass thickness and n G denote the refractive index of the glass substrate of the second microlens array and where f (i) denotes the focal length of the i-th microlens of the second microlens array and where d LThe distance between the second microlens array and the optical wedge is given by: i = 1...n. Using this formula, all focal lengths of the total n microlenses of the first microlens array can be easily calculated based on the optical properties of the total n microlenses of the second microlens array. The denominator typically has a negative sign, so the focal lengths f1 (i) All microlenses of the first microlens array have a positive sign and are therefore convex in shape. Preferably: dGnG+dL <f(i)

[0014] In a preferred embodiment, it is proposed that for the distances d12(i+1) The following applies between the microlenses of the first microlens array and the microlenses of the second microlens array: d12(i+1)=2(f(i)+p(i)2tan(α))β(2f(i)p(i)−tan(α)) where p (i)the midpoint between the i-th microlens and the i+1-th microlens, f (i) The focal length of the i-th microlens of the second microlens array and β denote the numerical aperture of the second microlens array, where i = 1...n-1. The distances d12(i+1), which are typically in the micrometer or millimeter range, are thus determined by a recursive formula and depend in particular on optical properties (focal point and numerical aperture) and geometric properties (center distance) of the microlenses of the second microlens array.

[0015] In an advantageous embodiment, it is proposed that the angle of inclination α is chosen such that: β2 <arcsin[nG sin{α−arcsin(sin[α]nG)}] where β is the numerical aperture and n GThe refractive index of the second microlens array is specified. Preferably, |α| should be < 15°, since larger angles may cause aberrations that would need to be compensated for by additional measures.

[0016] In an advantageous embodiment, the optical wedge can be designed to be translationally movable and / or rotatable about an axis extending in a second direction. This allows the optical wedge to finely adjust the optical path length of the laser light through dynamic adjustment, in particular rotation and / or translation, for example, during the processing of a workpiece with a laser device that includes at least one device for homogenizing laser light as presented here. This, in particular, makes it possible to influence the resulting surface finish of the workpiece being processed in real time.

[0017] It should also be noted that it is possible to use corresponding micromirror arrays in combination with a refractive optical wedge instead of microlens arrays. In this case, it is particularly advantageous to align the micromirror arrays with the incident laser light parallel to a curvature apex in order to reduce astigmatism.

[0018] An arrangement according to the invention comprises a plurality of devices for homogenizing laser light according to any one of claims 1 to 9, wherein the devices are arranged side by side in the first direction and devices adjacent to each other are designed such that the plane of the lens vertices of the second microlens array is alternately inclined by an angle +α and by an angle -α to the plane of the lens vertices of the first microlens array.

[0019] In a preferred embodiment, it is proposed that an even number of devices be arranged side by side. Such an arrangement of an even number of devices for homogenizing laser light, in the case of a laser device capable of generating a line-like intensity distribution in a working plane, results in the superposition of an even number of linear intensity profiles of the laser light in the working plane, all exhibiting the same slope but with opposite signs. This allows linear macro-inhomogeneities to be compensated for particularly advantageously, so that the resulting intensity profile in the working plane is again homogenized.

[0020] Alternatively, the elimination of macro-inhomogeneities can also be achieved by pre-homogenizing the laser light, since the scanning effect no longer makes a significant contribution when the device is illuminated almost homogeneously. In this case, for example, only one device or an odd number of devices could be used to homogenize the laser light.

[0021] Furthermore, it is possible to eliminate macro-inhomogeneities by asymmetrically adapting, for example, a Gaussian beam profile (especially one corresponding to a Weibull distribution) of the laser light. For this to work, the asymmetry of the beam profile must be matched to the width modulation of the microlenses in the microlens arrays, which is associated with the tilt angle.

[0022] Further features and advantages of the present invention will become clear from the following description of preferred embodiments with reference to the accompanying figures. These show: Fig. 1 A schematically very simplified representation of a laser device by means of which a line-shaped intensity distribution can be generated in a working plane, Fig. 2 a top view of an arrangement of two devices for homogenizing laser light in a first configuration, Fig. 3 a top view of an arrangement of two devices for homogenizing laser light in a second configuration, Fig. 4 a top view of a first of the two devices for homogenizing laser light according to Fig. 2 and Fig. 3, Fig. 5 a detailed view showing the path of two partial beams of laser light through two spaced-apart microlenses and an optical wedge, Fig. 6 a top view of an arrangement with a number m > 2 of devices for homogenizing laser light.

[0023] For clarity, a Cartesian coordinate system has been drawn in each figure. A y-axis extends perpendicularly to the plane of the drawing.

[0024] Before details of a device 1.1-1.m for homogenizing laser light 2.1-2.m and an arrangement 103 formed therefrom of a number m ≥ 2 such devices 1.1-1.m are described in more detail below, the following will be referred to Fig. 1 First, some basic principles are explained in which a line-shaped intensity distribution of the laser light 2.1-2.m can be generated in a working plane 105 by means of a laser device 100 equipped with the arrangement 103.

[0025] Fig. Figure 1 shows the structure of a corresponding laser device 100 in a schematically very simplified form and without explicitly showing, for example, individual laser beams or details of the optical components of the laser device 100, in particular specific shapes of optically functional surfaces of the optical components.

[0026] Typically, the laser device 100 comprises a laser light source 101 with a plurality of laser modules 101.1, 101.2, ..., 101.m or laser emitters, wherein the laser light 2.1-2.m emitted by these laser modules 101.1, 101.2, ..., 101.m or laser emitters during operation preferably has similar, but not necessarily identical, beam profiles. During operation, the laser modules 101.1, 101.2, ..., 101.m or laser emitters of the laser light source 101 illuminate a beam transformation device 102, which comprises a plurality of optical means for beam shaping configured to generate an at least partially linear intensity distribution in angular space. Such beam transformation devices 102 are known from the prior art in very different embodiments and will therefore not be explained further here.

[0027] After this beam shaping, the laser light 2.1-2.m passes through an arrangement 103 comprising a number m ≥ 2 of devices 1.1-1.m for homogenizing the laser light 2.1-2.m, which will be explained in more detail below, and subsequently through at least one Fourier lens 104 arranged downstream of the arrangement 103 in the direction of beam propagation of the laser light 2.1-2.m. This Fourier lens 104 serves the purpose of generating the linear intensity distribution of the laser light 2.1-2.m in spatial space within a working plane 105 arranged downstream of the Fourier lens 104 in the direction of beam propagation, in which a workpiece to be processed is located. The special feature is that by using the arrangement 103 with a preferably even number m ≥ 2 of devices 1.1-1.m for homogenizing laser light 2.1-2.m, the line length and the flank shape of each individual line of the laser light 2.1-2.The parameter m can be adjusted so that a linear intensity distribution can be generated in the working plane 105 by superimposing the individual lines of the laser light 2.1-2.m. The combined partial lines of the laser light 2.1-2.m thus result in a homogeneous linear intensity distribution in the working plane 105.

[0028] The following will refer to Fig. 2, Fig. 3, Fig. 4 to Fig. 5 further details of an arrangement 103 of two devices 1.1, 1.2 for homogenizing laser light 2.1, 2.2 will be explained in more detail. Fig. 2 and Fig. Figure 3 shows two different configurations of the two devices 1.1, 1.2 for homogenizing laser light 2.1, 2.2, which form the arrangement 103.

[0029] In general, the arrangement 103 may preferably have an even number m ≥ 2 such devices 1.1-1.m. As in Fig. 2 and Fig. As can be seen in Figure 3, the two devices 1.1 and 1.2, arranged side by side in the x-direction, are designed such that they are each mirror-symmetrical with respect to a yz-plane extending between them. The two configurations shown there differ from each other in that the positions of devices 1.1 and 1.2 are interchanged.

[0030] Each of the two devices 1.1, 1.2 has a first microlens array 3 with a number n of microlenses 30.1-30.n, which are arranged side by side in a first direction (x-direction) and are designed as cylindrical lenses whose cylinder axes are oriented substantially parallel to each other. Furthermore, each of the two devices 1.1, 1.2 has a second microlens array 4, which is spaced apart from the first microlens array 3 in the direction of propagation of the laser light 2.1, 2.2 (z-direction) and comprises a number n of microlenses 40.1-40.n, which are also arranged side by side in the first direction (x-direction) and are designed as cylindrical lenses whose cylinder axes are oriented substantially parallel to each other. The cylinder axes of the microlenses 30.1-30.n, 40.1-40.n, which are designed as cylindrical lenses, aren extend in a second direction (y-direction) perpendicular to the first direction (x-direction) and perpendicular to a third direction (z-direction), which defines the beam propagation direction of the laser light 2.1, 2.2.

[0031] The number n of microlenses 30.1-30.n of the first microlens array 3 corresponds to the number n of microlenses 40.1-40.n of the second microlens array 4. In other words, each of the microlenses 40.1-40.n of the second microlens array 4 corresponds to a microlens 30.1-30.n of the first microlens array 3, such that during the operation of the devices 1.1, 1.2, partial beams 20, 21 of the laser light 2.1, 2.2 that have passed through an i-th microlens 30.i (i = 1...n) of the first microlens array 3 pass at least mostly through an i-th microlens 40.i (i = 1...n) of the second microlens array 4. This situation is in Fig. Figure 5 shows in detail. To simplify the presentation, microlens arrays 3 and 4, comprising a number n = 7 of microlenses 30.1-30.n and 40.1-40.n, were chosen for the description of the exemplary embodiments. It is understood that this number is merely exemplary.

[0032] For example, alternative embodiments may also use acylindrical or spherical microlenses 30.1-30.n, 40.1-40.n, whereby the complexity of the overall optical structure increases even further, particularly in the case of a spherical design.

[0033] Furthermore, the two devices 1.1, 1.2 for homogenizing laser light 2.1, 2.2 each have an optical wedge 5 which is spaced away from the second microlens array 4 and is thus arranged behind the second microlens array 4 in the direction of propagation of the laser light 2.1, 2.2.

[0034] As particularly in Fig. 2 and Fig. As can be seen in Figure 3, the plane 41 of the lens vertex of the second microlens array 4 is inclined relative to the plane 31 of the lens vertex of the first microlens array 3 by an angle |α| in both configurations shown there, such that the distances of the microlenses 30.1-30.n of the first microlens array 3 from the corresponding microlenses 40.1-40.n of the second microlens array 4 vary. In the first device 1.1, the plane 41 of the lens vertex of the second microlens array 4 is inclined relative to the plane 31 of the lens vertex of the first microlens array 3 by an angle +α in both configurations, and in the second device 1.2, the plane 41 of the lens vertex of the second microlens array 4 is inclined in the opposite direction relative to the plane 31 of the lens vertex of the first microlens array 3 by an angle -α.

[0035] The microlens arrays 3, 4 of the two devices 1.1, 1.2 for homogenizing laser light 2.1, 2.2 are configured such that the devices 1.1, 1.2 each have a focal plane 6 in an air gap 7 between the second microlens array 4 and the optical wedge 5. For this purpose, the microlens arrays 3, 4 in the embodiments shown here are configured such that the focal lengths or diameters of the microlenses 30.1-30.n, 40.1-40.n increase successively in the first direction (x-direction) from the first microlens 30.1, 40.1 to the nth microlens 30n, 40n. In general, the microlens arrays 3, 4 can be designed such that the focal lengths or diameters of the microlenses 30.1-30.n, 40.1-40.n change in the first direction (x-direction) starting from the first microlens 30.1, 40.1 to the nth microlens 30n, 40n, so that an ascending or descending order of the microlenses 30.1-30.n, 40.1-40.n according to focal lengths or diameters in the first direction is not mandatory, although it is preferred, especially for manufacturing reasons.

[0036] Due to the inclination of the plane 41 of the lens vertex of the second microlens array 4 to the plane 31 of the lens vertex of the first microlens array 3 by the angle |α|, the distance of the first microlens 30.1 (shortest focal length) of the first microlens array 3 from the corresponding first microlens 40.1 (shortest focal length) of the second microlens array 4 is the minimum distance between the two microlens arrays 3, 4 of both devices 1.1, 1.2. Conversely, the distance of the nth microlens 30.n (longest focal length) of the first microlens array 3 from the nth microlens 40.n (longest focal length) of the second microlens array 4 is the maximum distance between the two microlens arrays 3, 4 of the devices 1.1, 1.2.

[0037] By positioning the focal plane 6 in the air gap 7 between the second microlens array 4 and the optical wedge 5, the energy density in the glass substrates of the optically functional components, particularly in the second microlens array 4 and the optical wedge 5, and also on their surfaces, can be significantly reduced. This makes it possible for the devices 1.1, 1.2 presented here for homogenizing laser light 2.1, 2.2, or the arrangement 103 formed from them, to be used for homogenizing laser light 2.1, 2.2 at high power without damaging the glass substrates and the surfaces of the optically functional components, in particular the second microlens array 4 and the optical wedge 5, the devices 1.1, 1.2, or the arrangement 103 formed from them.

[0038] The optical wedge 5 has a light-entry surface 50 that is oriented parallel to the plane 41 of the lens vertex of the second microlens array 4 and is therefore also inclined by the angle |α| – that is, by the angle +α in the first device 1.1 and by the angle -α in the second device 1.2 – to the plane 31 of the lens vertex of the first microlens array 3. The optical wedge 5 can advantageously be used for fine-tuning the optical path length of the laser light 2.1, 2.2 and thus also for fine-tuning and compensating for possible micro-inhomogeneities. This measure advantageously allows the surface quality of the workpieces to be processed by the laser device 100 to be improved in real time. The optical wedge 5 can be moved in the millisecond range for this purpose. Because the devices 1.1, 1.2 presented here are used for homogenizing laser light 2.1, 2.2, the optical wedge 5 can be moved in the millisecond range.Since the microlens arrays 3 and 4 are not monolithic, it is possible to adjust the line length and compensate for decentering errors within certain limits.

[0039] The well-defined common focal plane 6 within the air gap 7 between the second microlens array 4 and the optical wedge 5, which is located at a distance d L The position behind the second microlens array 4 can be achieved by adjusting the radii of curvature or focal lengths of the microlenses 30.1-30.n of the first microlens array 3. The focal length can be adjusted accordingly. f1(i) The i-th of the total n microlenses 30.1-30.n of the first microlens array 3 can be calculated as follows: f1(i)=−(f(i))2dGnG+dL−f(i)

[0040] In this formula, d denotes G the glass thickness and n G the refractive index of the glass substrate of the second microlens array 4. Furthermore, f denotes(i) the focal length of the i-th of the total n microlenses 40.1-40.n of the second microlens array 4. The following always applies: f1(i)>f(i).

[0041] Preferably the following applies: dGnG+dL <f(i)

[0042] As mentioned above, the optical wedge 5, which is arranged downstream of the second microlens array 4 in the beam propagation direction, has a light entrance surface 50 that is parallel to the plane 41 of the lens vertex of the second microlens array 4 and is therefore also inclined by the angle |α| to the plane 31 of the lens vertex of the first microlens array 3. This advantageously ensures phase differences of individual partial beams of the laser light 2.1, 2.2, thereby minimizing interference-induced micro-inhomogeneities. Furthermore, the optical wedge 5 can easily correct an angular misalignment induced by the second microlens array 4.

[0043] The angle of inclination α should advantageously meet the following criterion: β2 <arcsin[nG sin{α−arcasin(sin[α]nG)}]

[0044] Here, β denotes the numerical aperture of the second microlens array 4, which is the same for all microlenses 40.1-40.n. The thickness of the optical wedge 5 at its thinnest point can, in principle, be chosen arbitrarily. Preferably, |α| should be < 15°, since larger angles may lead to aberrations that would need to be compensated for by suitable additional measures.

[0045] The distances d12(i+1) The two microlens arrays 3, 4, which are typically in the micrometer and millimeter range respectively, can be determined by a recursive relationship for which the following holds: d12(i+1)=2(f(i)+p(i)2tan(α))β(2f(i)p(i)−tan(α))

[0046] In this formula, p denotes(i) the center distance between the i-th microlens 40.i and the i+1-th microlens 40.i+1 (i = 1...n-1) of the second microlens array 4.

[0047] The arrangement 103 preferably has an even number m ≥ 2 of the devices 1.1-1.m presented here. The in Fig. 2 and Fig. The arrangements 103 shown in Figure 3 feature two such devices 1.1 and 1.2 as examples, which are designed to be mirror-symmetric with respect to the yz-plane running between them. This means, in the present case, for the first configuration according to Fig. 2, that the first microlens 30.1 of the first microlens array 3 of the first device 1a is arranged adjacent to the first microlens 30.1 of the first microlens array 3 of the second device 1b. For the second configuration according to Fig. 3, in which the positions of the two devices 1.1, 1.2 are compared to that in Fig. In the configuration shown, if the microlenses are interchanged, the nth microlens 30.n of the first microlens array 3 of the first device 1a is arranged next to the nth microlens 30.n of the first microlens array 3 of the second device 1b. The same applies in both configurations to the microlenses 40.1-40.n of the second microlens array 4.

[0048] An arrangement 103 implemented as described here leads to a superposition of the two linear intensity profiles of the laser light 2.1, 2.2 in the working plane 105, which have the same slope but different signs. This allows linear macro-inhomogeneities to be compensated for, so that the resulting intensity profile in the working plane 105 is again homogenized.

[0049] If the arrangement 103 has an even number m > 2 of such devices 1.1-1.m, these are placed in the Fig.The devices 1.1-1.m are arranged in a series as illustrated in Figure 6, whereby the mirror symmetry of adjacent devices 1.1-1.m, through which the laser light 2.1, 2.2 ..., 2m can pass, is always maintained. This means that adjacent devices 1.1-1.m are designed such that the plane 41 of the lens vertex of the second microlens array 4 is alternately inclined by an angle +α and by an angle -α to the plane 31 of the lens vertex of the first microlens array 3.

[0050] The elimination of macro-inhomogeneities can alternatively be achieved by pre-homogenizing the laser light 2.1-2.m, since the scanning effect no longer makes a significant contribution when the device 1.1-1.m is illuminated almost homogeneously. Then, for example, only one of the devices 1.1-1.m or an odd number of devices 1.1-1.m could be used to homogenize the laser light 2.1-2.m.

[0051] Furthermore, it is possible to eliminate the macro-inhomogeneities by asymmetrically adapting, for example, a Gaussian beam profile. For this, the asymmetry of the beam profile must be adapted to the width modulation of the microlenses 30.1-30.n, 40.1-40.n of the microlens arrays 3, 4, which is associated with the tilt angle.

[0052] Machining processes of workpieces, which are typically carried out with laser devices 100, which have such devices 1.1-1.m for homogenizing laser light 2.1-2.m or an arrangement 103 of an even number m ≥ 2 of such devices 1.1-1.m, are very sensitive with regard to intensity fluctuations (therefore, the suppression of interference-induced intensity fluctuations is also advantageous). These fluctuations cannot be completely suppressed with the devices 1.1-1.m for homogenizing laser light 2.1-2.m presented here, or with the arrangement 103 formed from them, but they only occur in a greatly attenuated form.

[0053] To further improve the optical properties of the laser light 2.1-2 m on the workpiece being processed in the working plane 105, the optical wedge 5 can be rotated around the y-axis during the processing. This makes it possible to impose a time-dependent angular offset on the resulting linear intensity distribution, so that the laser line resulting in the working plane 105 can be moved back and forth, for example, in the millisecond range, thereby reducing the contrast of the periodic pattern on the workpiece. In other words, this is a real-time manipulation of the optical path length. Furthermore, by varying the distance of the second microlens array 4 from the first microlens array 3, the line length in the working plane 105 can be changed within a certain range.

Claims

[1] Device (1.1-1.m) for homogenizing laser light (2.1-2.m), comprising - a first microlens array (3) with a plurality of microlenses (30.1-30.n) arranged side by side in a first direction, - a second microlens array (4) with a plurality of microlenses (40.1-40.n) arranged side by side in the first direction, wherein the second microlens array (4) is arranged at a distance from the first microlens array (3) in the direction of propagation of the laser light (2.1-2.m) and the plane (41) of the lens vertex of the second microlens array (4) is inclined to the plane (31) of the lens vertex of the first microlens array (3) by an angle |α| and wherein the microlens arrays (3,4) are configured such that the focal lengths of the microlenses (30.1-30.n, 40.1-40.n) arranged next to each other in the first direction change from the first microlens (30.1, 40.1) to the nth microlens (30n, 40n),characterized by , that in the direction of beam propagation an optical wedge (5) is arranged behind the second microlens array (4) and the focal lengths of the microlenses (30.1-30.n, 40.1-40.n) of the microlens arrays (3, 4) are selected such that a focal plane (6) of the device (1.1-1.m) lies in an air gap (7) between the second microlens array (4) and the optical wedge (5). [2] Device (1.1-1.m) according to claim 1, characterized by , that the microlens arrays (3, 4) are designed such that the focal lengths of the microlenses arranged next to each other in the first direction (30.1-30.n, 40.1-40.n) increase successively from the first microlens (30.1, 40.1) to the nth microlens (30n, 40n). [3] Device according to one of claims 1 or 2, characterized by, that the number of microlenses (30.1-30.n) of the first microlens array (3) corresponds to the number of microlenses (40.1-40.n) of the second microlens array (4), such that each of the microlenses (40.1-40.n) of the second microlens array (4) is assigned a microlens (30.1-30.n) of the first microlens array (3). [4] Device (1.1-1.m) according to any one of claims 1 to 3, characterized by , that the microlenses (30.1-30.n, 40.1-40.n) are designed as cylindrical lenses, whose cylinder axes are each oriented in a second direction perpendicular to the first direction and perpendicular to a third direction which defines the beam propagation direction of the laser light (2.1-2.m). [5] Device (1.1-1.m) according to any one of claims 1 to 4, characterized by , that the optical wedge (5) has a light entry surface (50) oriented parallel to the plane (41) of the lens vertex of the second microlens array (4). [6] Device (1.1-1.m) according to any one of claims 1 to 5, characterized by that for the focal length f1(i) The i-th microlens (30.i) of the first microlens array (3) is: f1(i)=−(f(i))2dGnG+dL−f(i) where d G the glass thickness and n G denote the refractive index of a glass substrate of the second microlens array (4) and where f (i) denotes the focal length of the i-th microlens (40.i) of the second microlens array (4) and where d L the distance between the second microlens array (4) and the optical wedge (5) is and where: i = 1...n. [7] Device (1.1-1.m) according to any one of claims 1 to 6, characterized by , that for the distances d12(i+1) between the microlenses (30.1-30.n) of the first microlens array (3) and the microlenses (40.1-40.n) of the second microlens array (4), the following applies: d12(i+1)=2(f(i)+p(i)2tan(α))β(2f(i)p(i)−tan(α)) where p(i) the center distance between the i-th microlens (40.i) and the i+1-th microlens (40.i+1) and f (i) denote the focal length of the i-th microlens (40.i) and β the numerical aperture of the second microlens array (4), where i = 1...n-1. [8] Device (1.1-1.m) according to any one of claims 1 to 7, characterized by , that the angle of inclination α is chosen such that: β2 <arcsin[nG sin{α−arcsin(sin[α]nG)}] where β is the numerical aperture and n G denote the refractive index of the second microlens array (4). [9] Device (1.1-1.m) according to any one of claims 1 to 8, characterized by , that the optical wedge (5) is designed such that it is translationally movable and / or rotatable about an axis extending in the second direction. [10] Arrangement (103) of a plurality of devices (1.1-1.m) for homogenizing laser light (2.1-2.m) according to any one of claims 1 to 9, wherein the devices (1.1-1.m) are arranged side by side in the first direction and wherein adjacent devices (1.1-1.m) are designed such that the plane (41) of the lens vertex of the second microlens array (4) is alternately inclined to the plane (31) of the lens vertex of the first microlens array (3) by an angle +α and by an angle -α. [11] Arrangement (103) according to claim 10, characterized by , that an even number of devices (1.1-1.m) are arranged next to each other.

Images