Optical assembly for converting an input laser beam into a linear output beam with more homogeneity in intensity profile - Patents.com

Abstract

The present invention relates to an optical assembly (20) for converting an input laser beam (18) into a linear output beam (12) having a more homogeneous intensity distribution. The present invention also relates to a laser system (10) for generating a linear output beam (12) having such an intensity distribution, comprising such an optical assembly (20). Furthermore, the present invention relates to a method for controlling a displacement device (54) for one of two lens arrays (38, 40) in the optical assembly (20).

Description

[Technical field]

[0001] The present invention relates to an optical assembly for converting an input laser beam into a linear output beam, a laser system including such an optical assembly, and a method for controlling a displacement device in at least one of two lens arrays in an optical assembly for converting an input laser beam into a linear output beam. [Background technology]

[0002] The laser system serves to generate a particularly high intensity beam having a beam cross section whose intensity profile extends linearly. In the following, the axis defined by the linear expansion is referred to as the "major axis" of the intensity profile. The axis perpendicular to the linear expansion and perpendicular to the expansion direction is also referred to as the "minor axis".

[0003] To describe the geometric proportions of the beam, a respective local coordinate system is adopted, with the major axis (x), minor axis (y) and propagation direction (z) defining an oriented right-handed Cartesian coordinate system.

[0004] The linear beam profile described above is used, for example, to process (for example, temper, anneal) glass or semiconductor surfaces. In this case, the linear beam profile is scanned substantially perpendicular to the long axis over the surface to be processed. The irradiation can, for example, cause recrystallization processes, surface melting, diffusion processes of impurities into the material to be processed, or phase transitions in areas of the surface. Such processing processes are used, for example, in the manufacture of TFT displays, doping of semiconductors, the manufacture of solar cells, but also for producing aesthetically finished glass surfaces for architectural applications.

[0005] For the above mentioned processing process, it is important that the intensity profile along the major axis has a substantially constant intensity progression as homogeneous as possible, and that the intensity profile along the minor axis meets the corresponding quality requirements. However, in practice, the intensity profile usually has local inhomogeneities in the intensity progression, which are caused, for example, by interference artifacts (e.g. regular diffraction patterns) and / or by defects and shape errors (e.g. aberration errors) of the optical system and / or by contamination of the optical system by particles (resulting in projections on the working surface).

[0006] In order to reduce interference artifacts, an optical assembly is known from US Pat. No. 5,399,633, which makes it possible to provide a very homogeneous intensity profile according to the preamble of claim 1. Nevertheless, it would be desirable to provide an even more homogeneous intensity profile than is possible with the known optical assembly. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Patent No. 102020108647(A1) Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to provide an intensity profile that is more homogeneous than in the prior art with a corresponding optical assembly and a corresponding laser system. [Means for solving the problem]

[0009] The problem is solved by an optical assembly according to claim 1. Thus, an optical assembly for converting an input laser beam into a linear output beam propagating along a propagation direction and having a linear beam cross-section with a non-zero intensity expanded along a linear direction in a working plane, the optical assembly comprising a shaping optic having an input aperture into which the input laser beam can be incident and an output aperture, the shaping optic being configured to convert the input laser beam incident through the input aperture into a beam packet having a number of beam segments exiting through the output aperture, a homogenizing optic and at least one transforming lens means, the homogenizing optic being configured to mix various beam segments of the beam packet along a linear direction and the transforming lens means being configured to superimpose the mixed beam segments into a linear output beam, the homogenizing optic being configured to mix the ... homogenizing optic being configured to mix the various beam segments of the beam packet together. An optical assembly is proposed, comprising a homogenization optics system including a first lens array and a second lens array arranged in a beam path downstream of the first lens array, a displacement device provided with an actuator, the actuator being controllable to displace the second lens array relative to the first lens array in accordance with a primary control mode of a control device of the displacement device, the control device having at least one auxiliary control mode, the at least one auxiliary control mode being configured to at least partially adapt a settable target frequency and / or target amplitude of the primary control mode of the displacement movement of the second lens array (more specifically, the actuator and of the second lens array by the actuator) in order to homogenize the linear output beam.

[0010] The optical assembly is therefore a device for converting an input laser beam into an output beam with a linear intensity profile. In this respect, the output beam propagates in a propagation direction (in spatial average) and has an intensity distribution with a beam cross-section whose progression is linear along a direction, which in the optical working plane of the optical assembly is referred to in this context as a "linear direction". Since the beam may be deflected one or more times according to the output beam when passing through the optical assembly, linear direction should be understood as the beam cross-section being elongated locally along a linear direction in its length.

[0011] The optical assembly includes a shaping optic having an input aperture into which the input laser beam can be incident, and an output aperture, the output aperture extending longitudinally along a longitudinal direction of the output aperture, the dimension of the output aperture along the longitudinal direction being significantly larger than the dimension perpendicular to the longitudinal direction of the output aperture.

[0012] The shaping optics is configured to convert the input laser beam entering through the input aperture into a beam packet exiting through the output aperture, in particular the beam packet forming an elongated intensity distribution already after the output aperture in a theoretical observation plane, in particular already having a substantially linear characteristic, the beam packet comprising a number of beam segments, which are in particular distributed over the preferably elongated output aperture, preferably filling the output aperture completely.

[0013] Beam packet in this context refers in particular to a light distribution that can be mathematically described by a vector field, each spatial point being locally assigned a corresponding Poynting vector of the electromagnetic field.

[0014] The shaping optics is particularly configured to generate, from a sufficiently coherent input laser beam, a beam packet having reduced spatial coherence, or even a substantially incoherent beam packet.

[0015] The properties of the output beam are also decisively influenced by the form of the shaping optics. The optical phenomena in the shaping optics are complex and are especially influenced by the spatial coherence of the light distribution, which is in turn decisive for the formation of disruptive interference artifacts. Advantageously, the shaping optics is configured to be particularly incoherent, such that when an input laser beam with high spatial coherence enters through the input aperture, the beam packet exiting through the output aperture has a significantly reduced spatial coherence. Thereby, interference effects are reduced or completely avoided in the subsequent homogenization and / or focusing of the beam path, which allows further reduction of inhomogeneities in the intensity profile.

[0016] The optical assembly additionally includes a homogenization optics configured to overlap and mix various beam segments of the beam packet along a linear direction, so that the intensity profile is homogenized with respect to the direction in which the beam cross-section extends longitudinally.

[0017] The homogenizing optics includes a first lens array and a second lens array arranged in the beam path downstream of the first lens array. Lens array in this context refers in particular to an assembly of a plurality of lenses. The assembly of lenses may be irregular or the lenses may be arranged next to each other in a regular pattern.

[0018] The first lens array and the second lens array may each have a plurality of cylindrical lenses extending along the respective cylinder axes. In order to mix the beam segments of the beam packet particularly effectively, it is particularly advantageous if the cylindrical lenses are geometrically dimensioned in such a way that the beam packet impinges on a plurality of cylindrical lenses arranged next to one another. Effective homogenization can be achieved, for example, by the respective cylinder axes extending perpendicular to the propagation direction and perpendicular to the linear direction. In particular, the cylindrical lenses are configured such that there is no curvature along the respective cylinder axes.

[0019] The optical assembly further comprises a transforming lens means arranged in the beam path downstream of the homogenizing optics. The transforming lens means is configured to superimpose the mixed beam segments into a linear output beam for homogenization. In this respect, the transforming lens means also contributes in particular to homogenization. In addition to this, for example, the working surface can extend to the focal region of the transforming lens means. For example, it is conceivable to focus the beam segments from each region of the captured beam in various regions along a linear direction, preferably in all regions.

[0020] The conversion lens means is in particular configured to superimpose the beam segments (intermediate beam segments) mixed by the homogenizing optics into a linear output beam, so that the desired linear intensity distribution is obtained at the working surface. For this purpose, the conversion lens means is preferably configured as a reflective Fourier optics or as a Fourier lens (in particular acting in a non-imaging manner). For example, it can be configured as a Fresnel zone plate.

[0021] The optical assembly further includes a displacement device, the displacement device configured to displace the second lens array of the homogenizing optics relative to the first lens array of the homogenizing optics. For the displacement, the displacement device has an actuator controlled by the control device. The actuator is movably coupled to the second lens array within a range in which operation of the actuator causes movement of the second lens array or displacement of the second lens array relative to the first lens array. The actuator may be a motor. The actuator may be, for example, a voice coil, a piezo actuator, and / or other linear motor.

[0022] The displacement device may further include a housing frame and a holding device for holding the second lens array. The holding device may in particular be slidably supported on the housing frame. Such a configuration is robust and allows a secure holding of the second lens array even with a relatively fast displacement. Advantageously, the holding device is supported on the housing frame so that it can slide back and forth along a linear direction. In that case, it is preferred if the holding device is supported on the housing frame, for example, via at least one solid bearing. Support via a rolling bearing or support using an air spring is also conceivable. The support basically allows the holding device to be displaced back and forth in a reciprocating movement relative to the housing frame. In this respect, the displacement device is configured in such a way that the holding device can reciprocate back and forth relative to the housing frame. In this connection, it is particularly preferred if the stiffness of the support (for example at least one solid bearing) is adapted to the frequency of the reciprocating movement of the holding device relative to the housing frame. However, the stiffness for adapting to the reciprocating movement may also be provided by a separate spring element connecting the holding device to the housing frame.

[0023] The displacement of the second lens array relative to the first lens array acts inter alia on a change in the intensity distribution of the (mixed) beam packet exiting the homogenization optics (hereinafter the mixed beam packet exiting the homogenization optics is also referred to as the "intermediate beam packet") In particular, the displacement of the second lens array relative to the first lens array acts on a change in the angular distribution of the beam segments of the intermediate beam packet and / or on a spatial shift of the beam centroid of the intermediate beam packet (i.e. the centroid of the intensity distribution over the beam cross section of the entire intermediate beam packet).

[0024] A change in the angular distribution of the beam segments of the intermediate beam packet (in other words a change in the propagation direction of the intermediate beam packet) results in the intermediate beam packet impinging at a change in angle on the transforming lens means following the homogenizing optics in the beam path. Such an angle change on the transforming lens means results, inter alia, in a spatial shift of the beam centroid of the output beam. That is to say, in other words, the displacement of the second lens array relative to the first lens array can spatially shift the beam centroid of the output beam. Thus, the time-dependent displacement of the second lens array relative to the first lens array can spatially shift the output beam in a time-dependent manner and thus average out and smooth out disruptive interference effects in time.

[0025] On the other hand, a spatial shift of the beam centroid of the intermediate beam packet results in the intermediate beam packet impinging on the redirecting lens means at a changed position. Such a spatial shift of the intermediate beam packet results, inter alia, in a change in the angular distribution of the beam components of the output beam. In other words, a change in the spatial position of the intermediate beam packet causes a change in the propagation direction of the output beam.

[0026] In this respect, such areas (e.g. further optical means) arranged in the beam path downstream of the optical assembly can be illuminated from different directions by the time-dependent displacement of the second lens array relative to the first lens array. Thus, contamination in the beam path after the optical assembly (e.g. contamination by particles on the subsequent optical means) is likewise illuminated from different directions in a time-dependent manner, so that the projection resulting from this contamination changes in a time-dependent manner and is thus smoothed on average. This allows the reduction of inhomogeneities in the intensity progression caused by the projection. In addition to this, the reduction of inhomogeneities resulting from the geometrical inaccuracies of the optical system.

[0027] Overall, an optical assembly of this kind, whose displacement device is operated in a control mode, referred to herein as the primary control mode, makes it possible to average out and smooth out local inhomogeneities in the intensity distribution in time and thus achieve significantly improved process results during the surface processing of the workpiece, but in addition to this, the control device also includes at least one auxiliary control mode.

[0028] In that case, a control mode is understood to be an operation of the control device, which is used on the side of the control device to give the actuator corresponding instructions or control commands. The operation or control mode can be stored in a corresponding memory in the control device, which can be implemented in particular as a computer, or in the displacement device, and can be called up for use. When using a control mode, the actuator can use a control command transferred to the actuator corresponding to the respective control mode, thus affecting a periodic displacement of the second lens array relative to the first lens array, the displacement movement proceeding in particular in a repetitive movement pattern, depending in its actual frequency and / or actual amplitude on the setting in the form of a control command of the control mode. In this respect, the control command includes the setting of a target frequency and / or a target amplitude for the actuator or for the second lens array movably connected by the actuator. Deviations can occur between the target values ​​and the actual values, which in this respect lead to their different values.

[0029] Thus, the main control mode and at least one auxiliary control mode are respectively operations of the control device, which operations determine the setting of the target frequency and / or the target amplitude and more specifically their change, i.e. the change of the respective settings. While the main control mode here essentially controls the periodic displacement of the second lens array relative to the first lens array, i.e. in particular which target frequency and / or target amplitude should be used, and thus while the displacement device functions solely in the main control mode, the at least one auxiliary control mode brings about a homogenization of the intensity distribution of the linear output beam over a pure displacement movement, in particular an improvement of the displacement movement for improving the homogenization of the intensity distribution of the linear output beam, by at least partially adapting or correcting the target frequency and / or target amplitude set by the main control mode. That is, the target frequency and / or target amplitude set by the main control mode are adapted in the direction of a higher homogeneity of the intensity distribution of the linear output beam. This is particularly appropriate when the target frequency and / or target amplitude change, as occurs in particular when the target frequency and / or target amplitude change. To that end, depending on the auxiliary control mode, different adaptation strategies or schemes can be used, as will be explained in detail below. In that case, the main control mode and the auxiliary control mode may each be implemented by the control device separately from one another or implemented in combination as the same control mode. In this respect, it is not necessary that there are different control modes that are precisely separable in physical terms, e.g. as program code, but rather their functional principle is decisive instead, as described herein.

[0030] In order to achieve a particularly homogeneous intensity progression along the linear direction, it is preferred if the displacement device is configured such that the second lens array is moved back and forth along the linear direction. In that case, the beam centroid of the output beam is likewise moved back and forth along the linear direction, i.e. along the longitudinal axis. The back and forth movement is preferably performed with a varying, in particular randomly varying, target frequency and / or target amplitude.

[0031] Preferably, the displacement device is configured to displace the second lens array with a repeating movement pattern relative to the first lens array. In particular, the time scale of the change is short enough to effectively affect a spatially homogeneous intensity along a linear direction, compared with the process times of the application field of the optical assembly. Repeating, in particular, means that an initial configuration is used or implemented many times, being a kind of reciprocating movement. This reciprocating movement may essentially be periodic or may be aperiodic. It is conceivable that the second lens array moves back and forth around a reference point. Preferably, the repetitive movement is not performed periodically with a defined frequency, but instead in a particularly chaotic manner, with a fluctuating, in particular randomly fluctuating frequency and / or amplitude. Preferably, the main frequency contribution is in the range of 50-150 Hz, in particular in the range of 75-125 Hz (which in this context means in particular that the Fourier spectrum of the movement pattern has a relatively high amplitude at the so-called main frequency contribution).

[0032] Preferably, at least one auxiliary control mode is configured to adapt the target frequency and / or the target amplitude according to a set adaptation scheme of the at least one auxiliary control mode. This means that the set target frequency and / or the target amplitude can always be adapted according to the same scheme, which is set in this respect by the respective auxiliary control mode. Thus, in a simple manner, a known scheme can be used for the homogeneity improvement based on the adaptation of the target frequency and / or the target amplitude.

[0033] Advantageously, the first auxiliary control mode is configured such that the change of the target frequency set by the main control mode is carried out by a continuous target frequency change over time. Thus, apart from a non-continuous or sudden use of a new target frequency set by the main control mode, which may be lower or higher than the currently set target frequency, it is avoided that the actuator has to generate a particularly high force for this. Instead, the force for the displacement movement provided by the actuator can be continuously increased or decreased to achieve the respective change of the target frequency. Homogeneity can be improved by this measure, since large forces of the actuator, especially the maximum forces, which may lead to a deterioration of the homogeneity of the intensity distribution due to the stimulation of the system, are avoided. The adaptation scheme after the first auxiliary control mode is therefore such that for the target frequency change, a continuous transition in terms of time between the current target frequency and the set target frequency is always carried out.

[0034] In that case, the continuous target frequency change over time is preferably given by a slope of the change of the target frequency over a given period of time. Thus, in the progression of the frequency of the actuator over time between the actual target frequency and the set target frequency, a slope is discernible between both frequencies, which results in a continuous increase or decrease of the target frequency. The slope may in particular be a linear slope or may take the form of a straight line in the progression of the target frequency over time.

[0035] In this case, the predetermined period is preferably at least one period of the periodic displacement movement, and it has been shown that this minimum period is advantageously related to an increase in the homogeneity of the intensity profile of the linear output beam during the frequency change on the one hand, and to the time remaining for the displacement movement at each set target frequency between the target frequencies on the other hand.

[0036] Advantageously, the second auxiliary control mode is further configured to adapt the target amplitude set by the main control mode based on the allocation rule, so that the actuator executes an adapted target amplitude realizing an actual amplitude of the displacement of the second lens array, the actual amplitude being closer to the target amplitude set by the main control mode than when executing the target amplitude set by the main control mode. The second auxiliary control mode is based on the knowledge that the actuator can use the set target amplitude, possibly with only a significant deviation as the actual amplitude, especially when the frequency increases. In that case, the force demand of the actuator rises with the square of the frequency. By means of the allocation rule, this limitation can nevertheless be taken into account during the calibration. In that case, the allocation rule may be determined by simulation and / or experimentation and may be, for example, in the form of one or more mathematical functions, tables, graphs, etc.

[0037] The allocation rule can be configured in particular to allocate the actual amplitudes for different target frequencies to the respective adapted target amplitudes. The target amplitudes that can be set according to the main control mode are then the actual amplitudes that depend on the target frequencies but may not be achieved. The adapted target amplitudes are then allocated and used by the allocation rule, so that the desired actual amplitudes are also achieved. For example, the allocation rule can be a look-up table that allocates the respective target frequencies to the target amplitudes for different actual amplitudes. Setting the target amplitudes according to the allocation rule ensures that the desired actual amplitudes are achieved at least approximately.

[0038] Finally, the third auxiliary control mode is preferably configured such that the target amplitude change set by the main control mode is set with respect to a zero crossing of the displacement movement, which is particularly periodic, of the second lens array or of the actuator movably connected thereto. In other words, the set target amplitude is synchronized in time or the time point is set in such a way that a time point is at the zero crossing of the displacement movement, thereby ensuring a more gentle transition between each two set target amplitudes by the actuator. That is to say, instead of a respectively fixedly determined period between the target amplitude changes, the period is shortened or extended, in particular until the next zero crossing is reached. This makes it possible to avoid simultaneous loads due to high force responses at the actuator and thus at the target amplitude changes, which may further lead to non-homogeneity of the intensity profile of the linear output beam.

[0039] Although three auxiliary control modes, called first, second and third, have been described above, each of which may be used alone or in any combination or provided in the control device in order to homogenize the intensity profile of the linear output beam, it is then particularly advantageous to combine several or all of the auxiliary control modes in order to achieve the greatest possible homogenization of the intensity profile of the linear output beam.

[0040] Advantageously, the target frequency may be in the frequency range of 50-200 Hz, in particular in the range of 50-150 Hz, more particularly in the range of 75-125 Hz, which has been shown to be the optimal range with regard to the homogeneity of the intensity profile of the linear output beam and the achievable attenuation.

[0041] It is also preferred that the change in the target frequency, which can be set by the main control mode, does not exceed a maximum value of 25 Hz, in particular 20, more in particular 15 Hz, more particularly 10 Hz, which during the displacement movement has been shown to be optimal with regard to the homogeneity of the intensity profile of the linear output beam.

[0042] The problem set forth in the introduction is further solved by a laser system as set forth in claim 13. The laser system is configured to generate a linear output beam with an intensity distribution having a linear-shaped intensity profile in the beam cross-section. The laser system is provided by at least one laser source for emitting an input laser beam, and includes an optical assembly of the type described above for converting the input laser beam into a linear output beam, the optical assembly being arranged such that the input laser beam is provided by the laser source.

[0043] The laser source may be specifically adapted for or designed for multimode operation. The laser beam of the laser source may essentially be directly incident on the optical assembly. However, it is also conceivable that the laser system further comprises a pre-shaping optical system, by means of which the laser beam is deformed before it is incident on the optical assembly. The pre-shaping optical system may be configured, for example, as a collimator optical system. For example, the pre-shaping optical system may act anamorphically, so that the input laser beam has an elliptical beam cross section.

[0044] In this case, the features described herein with respect to the optical assembly apply equally to the laser system and vice versa.

[0045] The problem stated in the introduction is also solved by a method according to claim 14. The method is for controlling a displacement device with respect to one of two lens arrays in an optical assembly for converting an input laser beam into a linear output beam propagating along a propagation direction and having a linear beam cross-section with a non-zero intensity expanded along the linear direction in a working plane, the optical assembly comprising a shaping optic having an input aperture into which the input laser beam can enter and an output aperture, the shaping optic being configured such that the input laser beam entering through the input aperture is converted into a beam packet having a number of beam segments exiting through the output aperture, a homogenizing optic and at least one conversion lens means, the homogenizing optic mixing the various beam segments of the beam packet along the linear direction. the homogenization optics includes a first lens array and a second lens array arranged in a beam path downstream of the first lens array, the homogenization optics includes at least one transformation lens means, and a displacement device including an actuator and a control device, the displacement device including an actuator and a control device, the method comprising: controlling the displacement device using the control device according to a primary control mode to displace the second lens array relative to the first lens array, during which a target frequency and / or a target amplitude of the displacement movement of the second lens array set by the primary control mode is adapted by the at least one auxiliary control mode to homogenize the linear output beam.

[0046] In the method, the first auxiliary control mode may implement a change in the target frequency set by the primary control mode with a continuous change in the target frequency over time. Alternatively or additionally, the method is further configured to adapt the target amplitude set by the primary control mode based on the allocation rule, such that the actuator implements an adapted target amplitude that achieves an actual amplitude of the displacement of the second lens array, the actual amplitude being closer to the target amplitude set by the primary control mode than during implementation of the target amplitude set by the primary control mode. Alternatively or additionally, in the method, the third auxiliary control mode may implement a target amplitude set by the primary control mode with respect to a zero crossing of the displacement movement of the second lens array.

[0047] In this case, the features described herein with respect to the optical assembly and the laser system apply equally to the method and vice versa, in particular the method can be configured for implementation with the optical assembly described herein.

[0048] Further details and advantageous configurations of the invention will become apparent from the following description and will be described and explained in more detail on the basis of examples of the invention. [Brief description of the drawings]

[0049] [Figure 1] FIG. 1 is a schematic diagram illustrating a beam path in a laser system for generating a linear intensity distribution. [Diagram 2] 4 is a schematic diagram for explaining the operation of a homogenizing optical system and a conversion lens means. FIG. [Diagram 3] FIG. 2 is a schematic diagram illustrating the beam paths in the homogenizing optics and the transformation lens means when the second lens array is displaced relative to the first lens array; [Figure 4a] FIG. 4 is a diagram of the progression of the target frequency set for the actuator by the control device over time within the primary control mode of the control device. [Figure 4b]FIG. 13 is a diagram of an exemplary implementation of operations within the primary control mode. [Diagram 5] FIG. 13 is an exemplary progression of target frequency and displacement over time. [Figure 6] 13 is a graph of an exemplary actual amplitude versus target amplitude progression with respect to target frequency; [Figure 7] 1 is a graph showing the transition of the target amplitude and the actual amplitude together with their respective changes over time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] In the following description and in the drawings, identical or corresponding features are respectively labeled with the same reference numerals.

[0051] FIG. 1 shows, in a schematic diagram, a laser system 10 for generating a line beam 12 at a work plane 14, the line beam cross section having a non-zero intensity expanded along a linear direction (x-direction).

[0052] The laser system 10 includes at least one laser source 16 for emitting a laser beam. The laser source 16 is preferably configured as a multimode laser. The laser source 16 provides an input laser beam 18, optionally via pre-shaping optics (not shown). The pre-shaping optics can act, for example, in a collimating manner and / or can shape the laser beam into the input laser beam 18 having an elliptical beam cross-section. For example, it is conceivable that the laser beam is first transformed into the input laser beam 18 using deflecting mirrors and / or lens means.

[0053] The laser system 10 further includes an optical assembly 20 , using which the input laser beam 18 is converted into a linear output beam 12 .

[0054] To explain the geometric proportions, a Cartesian coordinate system (x,y,z) is shown in the drawings. In the illustrated example, the input laser beam 18 propagates along the z direction. The axis defined by the linear expansion of the output beam 12 extends along the x axis ("major axis"). The axis perpendicular to the linear direction and perpendicular to the direction of propagation is referred to as the "minor axis" (y axis).

[0055] For processing large surfaces, it may be desirable to achieve a linear intensity profile that extends over a very long distance. In this regard, it is conceivable that multiple laser systems (10, 10') of the type described above are provided and arranged to add intensity distributions along a longitudinally extending line.

[0056] The optical assembly 20 includes a number of optical components arranged downstream of one another in a beam path. As shown in a simplified manner in FIG. 1, the input laser beam 18 is first guided through a shaping optic 22, which shapes the input laser beam 18 into a beam packet 24. The beam packet 24 is then mixed and transformed into an intermediate beam packet 28 using a homogenizing optic 26. The intermediate beam packet 28 finally passes through a transforming lens means 30, which is arranged downstream of the homogenizing optic 26, and which transforms the intermediate beam packet 28 into a linear output beam 12 having a substantially homogenous intensity along a linear direction x.

[0057] Optionally, the optical assembly 20 additionally includes collimator / focusing optics 32 disposed in the beam path downstream of the conversion lens means 30 .

[0058] The shaping optics 22 has an input aperture 34 through which the input laser beam 18 can enter and an output aperture 36 through which the beam packet 24 can exit. In this case, the shaping optics 22 acts, among other things, to rearrange adjacent beam segments of the input laser beam 18 into beam segments of the beam packet 24 upon passing through the shaping optics 22.

[0059] Advantageously, the shaping optics 22 is configured to be particularly incoherent, such that when the input laser beam 18 having high spatial coherence enters through the input aperture 34, the beam packet 24 exiting through the output aperture 36 has a significantly reduced spatial coherence. For this purpose, the shaping optics 22 can be configured, for example, such that the beam segments of the beam packet 24 exiting through the exit aperture 40 have traveled different optical path lengths within the shaping optics 22. In particular, the difference in optical path lengths for the beam segments is large in comparison to the coherence lengths of the laser beams.

[0060] 2 shows the schematic construction and functional principle of the homogenizing optics 26 and the conversion lens means 30. The homogenizing optics 26 comprises a first lens array 38 and a second lens array 40 arranged in the beam path downstream of the first lens array 38. As exemplarily shown in FIG. 2, the lens arrays 38, 40 each have a number of cylindrical lenses 42, which extend along their respective cylindrical axes, which in the illustrated example are orthogonal to the drawing plane, i.e. orthogonal to the (local) propagation direction (z) and orthogonal to the (local) linear direction (x). The cylindrical lenses 42 are geometrically dimensioned such that the beam packet 24 impinges on the cylindrical lenses 42 arranged next to each other.

[0061] 2, the lens arrays 38, 40 are arranged such that the cylindrical lens 42 intercepts the beam packet 24 and mixes and overlaps with one another the various beam segments of the beam packet 24. The beam segments thus mixed and overlapped form an intermediate beam packet 28 which further impinges on a transformer lens means 30 disposed downstream of the homogenization optics 26.

[0062] The transformation lens means 30 is in particular configured to superimpose the beam segments of the intermediate beam packet 28 onto the linear output beam 12, so that a desired linear intensity distribution occurs at the working plane 14. For example, the transformation lens means 30 is preferably formed by a not shown Fourier lens 44. The Fourier lens 44 is in particular arranged such that the working plane 14 extends in the focal plane of the Fourier lens 44 (compare 2).

[0063] In particular, the mixing and superposition of the beam segments of the beam packet 24, preferably in cooperation with the shaping optics 22, which as described above sufficiently increases the coherence of the input laser beam 18, results in the output beam 12 being relatively homogeneous along the (local) linear direction x. Nevertheless, local inhomogeneities may occur in the intensity profile. For example, interference effects may result in periodic inhomogeneities in the intensity profile (compare the cutouts labeled with reference number 46 in FIG. 3). Furthermore, local contamination in the beam path (for example a particle 48 on the optical means 50 arranged downstream of the Fourier lens 44) may result in projections 52, which result in local inhomogeneities in the intensity profile.

[0064] As will be explained in more detail below, by displacing the second lens array 40 relative to the first lens array 38, the above-mentioned non-uniformities in the intensity profile can be reduced.

[0065] To displace the second lens array 40 relative to the first lens array 38, the optical assembly 20 comprises a displacement device 54 (schematically illustrated in Figures 2 and 3). The displacement device 54 is preferably configured to move the second lens array 40 back and forth relative to the first lens array 38, in particular along a linear direction x. To this end, the displacement device 54 comprises a schematic actuator 56 controlled by a corresponding control device 58. To that end, the control device 58 sets a target frequency and a target amplitude for the actuator 56.

[0066] The displacement of the second lens array 40 relative to the first lens array 38 acts, inter alia, on a change in the angular distribution of the beam segments of the intermediate beam packet 28 and / or on a spatial shift of the beam centroid of the intermediate beam packet 28 .

[0067] The change in the angular distribution of the beam segments of the intermediate beam packet 28 (in other words, the change in the propagation direction of the intermediate beam packet 28) causes the intermediate beam packet 28 to impinge at a changed angle on the Fourier lens 44 following the homogenization optics 26. Such an angular change at the Fourier lens 44 results, among other things, in a spatial shift of the beam centroid of the output beam 12 (illustrated exemplarily in dotted lines "downwards" with respect to the displacement of the second lens array at the bottom left of 3). In this respect, by a back-and-forth movement of the second lens array 40 relative to the first lens array 38, the beam centroid of the output beam 12 can be shifted back and forth spatially. In this way, non-uniformities based on interference effects can be smoothed out on average (schematically shown at the bottom left of FIG. 3).

[0068] The spatial shift of the beam center of gravity of the intermediate beam packet 28 results in the intermediate beam packet 28 impinging on the Fourier lens 44 at a changed position. Such a shift of the intermediate beam packet 28 results, inter alia, in certain areas of the Fourier lens 44 containing less intensity contributions of the intermediate beam packet 28, so that the light distribution of the output beam 12 acquires a favorable angle or asymmetry (illustrated exemplarily with respect to the shift of the intermediate beam packet 28 from the average reference position in the lower right of FIG. 3). In this respect, by the back and forth movement of the second lens array 40 relative to the first lens array 38, the propagation direction of the output beam 12 can be changed as a function of time. This results in that contamination 48 (e.g. dust particles) in the beam path after the Fourier lens 44 (e.g. on the subsequent optics 52) is illuminated from different directions as a function of time. In this respect, the projection 52 caused by such contamination 48 is also time-varying, so that, on average, the disturbing effect of the projection on the intensity progression can be smoothed out.

[0069] Figure 4a shows the progression of the target frequency set for the actuator 56 over time by the controller 58 within the primary control mode 60 of the controller 58. Figure 4b shows diagrammatically the execution of operations within the primary control mode 60 of the controller 58.

[0070] In the primary control mode 60, for example, a target frequency range of 100-150 Hz is adopted, in addition to which a change or jump in the target frequency f for the actuator 56, and thus for the second lens array 40 (see FIG. 2) displaced by the actuator 56, is permitted at a maximum jump width or maximum value of the target frequency change, in this example Δf=10 Hz.

[0071] The displacement movement of the second lens array 40 is in this case a periodic movement, in which a target frequency f is set for the actuator 56 with random variation according to the operation in FIG. 4b as part of the main control mode 60. For this, a random number is generated between 0 and 1 and multiplied by the maximum value of the target frequency change. The resulting frequency value is added to the previous target frequency f to form a new target frequency f. Before being set in the actuator 56, it is further verified whether the new target frequency f is within the determined frequency range. If it is within the frequency range, the new target frequency f is set in the actuator 56, which uses this new target frequency f and the second lens array 40 can oscillate in response to the new target frequency f or in response to the actual frequency that actually occurs or is real. If it is not within the frequency range, a new random number is generated between 0 and 1 and the operation is repeated.

[0072] In order to further improve the homogenization of the intensity profile of the linear output beam 12, according to Figures 5, 6 and 7 additional auxiliary control modes 62, 64, 66 are proposed which can be implemented by the control device 58, by means of which the target frequency change or the target amplitude change set by the main control mode 60 is adapted in order to further homogenize the intensity profile of the linear output beam 12.

[0073] FIG. 5 shows an exemplary progression of the target frequency f and its change over time t. Here, the setting of the target frequency f according to the main control mode 60 is presented by a straight line in the upper part of both graphs. However, according to the first auxiliary control mode 62, the setting of the target frequency f changes within the range of the target frequency change. Indeed, in this case, a continuous target frequency change 63 over time (for concreteness, the time range of the target frequency change is then called 63) is given to the actuator 56 in the form of a ramp to bring the target frequency f newly set according to the operation of FIG. 4b from the current or previous target frequency used by the actuator 56. As can be seen based on the lower graph, the period of the ramp is then set such that its period is the period time of the periodic displacement movement. Thus, unlike a discontinuous or abrupt use of the new target frequency set by the main control mode 60, it is avoided that the actuator 56 has to generate a particularly high force for that purpose. Instead, the force for the displacement movement provided by the actuator can be continuously increased or decreased to achieve the respective change of the target frequency. Homogeneity can be improved by this measure, since large forces of the actuator 56, in particular the maximum forces, which could lead to stimulation of the system leading to a deterioration of the homogeneity of the intensity distribution, are avoided.

[0074] FIG. 6 shows a graph of the progression of the target amplitude with respect to the target frequency f for an exemplary actual amplitude of 60 μm. In that case, the function shown and described in FIG. 6 in the form of a straight line, more specifically in the form of a linear function, is used as an allocation rule 65 of a second auxiliary control mode 64, not shown in detail. For a target amplitude of 60 μm by setting the target frequency f of the main control mode 60, typically an actual amplitude of 60 μm is expected. However, as can be seen based on FIG. 6, if the frequency is too low or too high, this actual amplitude is not achieved. By the second control mode 64, a target amplitude is selected, here according to the allocation rule 65, which ensures that at the set target frequency f, the desired actual amplitude is achieved by the actuator 56.

[0075] FIG. 7 shows, on the left, the course of the target amplitude with the respective displacement over time t according to the primary control mode 60. On the right, the course of the actual amplitude with the respective displacement over time t, depending on the adaptation of the target amplitude setting on the part of the control device 58 by the third auxiliary control mode 66. Comparing both courses of displacement over time t, it is recognizable that, by the third auxiliary control mode 66, the target amplitude change set by the primary control mode 60 is shifted to the zero crossing of the displacement of the actuator 56 or the second lens array 40. That is to say, by the third auxiliary control mode 66, the respective target amplitude (change) set by the primary control mode 60 is synchronized in time such that the target amplitude (change) is respectively at the zero crossing of the displacement movement and thus a smooth transition between the two respectively specified target amplitudes by the actuator 56 can be guaranteed. That is to say, instead of the respectively fixedly determined period between the target amplitude changes, as is the case in the left course of FIG. 7, in the right course of FIG. 7 this period is in particular shortened or extended until the next zero crossing is reached. This makes it possible to avoid high force responses in the actuator 56 and thus simultaneous loads due to the force responses in the target amplitude change, which could otherwise result in inhomogeneities in the intensity profile of the output beam 12.

Claims

1. 1. An optical assembly (20) for converting an input laser beam (18) into a linear output beam (12) propagating along a propagation direction (z) and having a linear beam cross-section with non-zero intensity expanded along a linear direction (x) at a working plane (14), the optical assembly (20) comprising: a shaping optical system (22) having an input aperture (34) into which the input laser beam (18) can be incident, and an output aperture (36), the shaping optical system (22) being configured such that the input laser beam (18) incident through the input aperture (34) is transformed into a beam packet (24) having a number of beam segments which exits through the output aperture (36); a homogenization optics (26) and at least one redirecting lens means (30), the homogenization optics (26) being configured to mix various beam segments of the beam packet (24) along the linear direction (x), the redirecting lens means (30) being configured to superimpose the mixed beam segments (28) onto the linear output beam (12), the homogenization optics (26) comprising a first lens array (38) and a second lens array (40) arranged in a beam path downstream of the first lens array (38); a displacement device (54) comprising an actuator (56), the actuator (56) being controllable to displace the second lens array (40) relative to the first lens array (38) according to a master control mode (60) of a control device (58) of the displacement device (54), the control device (58) having at least one auxiliary control mode (62, 64, 66) configured to at least partially adapt a target frequency and / or a target amplitude of the displacement movement of the second lens array (40) that can be set by the primary control mode (60) to homogenize the linear output beam (12).

2. The optical assembly (20) of claim 1, wherein the master control mode (60) is configured to set the target frequency and / or the target amplitude by random variation.

3. 3. The optical assembly (20) of claim 1 or 2, wherein the displacement device (54) is configured to displace the second lens array (40) relative to the first lens array (38) in a repeating, in particular periodically repeating or aperiodically repeating, movement pattern.

4. 4. The optical assembly (20) of claim 1, wherein the at least one auxiliary control mode (62, 64, 66) is configured to adapt the target frequency and / or the target amplitude according to an adaptation scheme of settings of the at least one auxiliary control mode (62, 64, 66).

5. 5. The optical assembly (20) of claim 1, wherein the first auxiliary control mode (62) is configured to implement the change in the target frequency set by the main control mode (60) based on a successive target frequency change (63) over time.

6. 6. The optical assembly (20) of claim 5, wherein the continuous target frequency change (63) over time is given by a slope of the change of the target frequency over a predetermined period of time.

7. The optical assembly (20) of claim 6, wherein the predetermined period is at least one period of a periodic displacement movement.

8. 8. The optical assembly (20) of claim 1, wherein the second auxiliary control mode (64) is configured to adapt the target amplitude set by the primary control mode (60) based on an allocation rule (65) so that the actuator (56) executes an adapted target amplitude that achieves an actual amplitude of the displacement of the second lens array (40), and the actual amplitude is closer to the target amplitude set by the primary control mode (60) than when the target amplitude set by the primary control mode (60) is executed.

9. 9. The optical assembly (20) of claim 8, wherein the allocation rule (65) is configured such that the allocation rule (65) allocates respective adapted target amplitudes to actual amplitudes for different target frequencies.

10. 10. The optical assembly (20) of claim 1, wherein a third auxiliary control mode (66) is configured to set a target amplitude change set by the primary control mode (60) with respect to a zero crossing of the displacement movement of the second lens array (40).

11. The optical assembly (20) according to any one of the preceding claims, wherein the target frequency to which the master control mode (60) can be set is in a predetermined frequency range of 50 to 200 Hz.

12. 12. The optical assembly (20) of any one of claims 1 to 11, wherein the change in the target frequency that the master control mode (60) can set does not exceed a maximum value of 25 Hz.

13. 1. A laser system (10) for generating a linear output beam (12) having an intensity distribution with a linear shaped intensity profile in a beam cross section, comprising: at least one laser source (16) for emitting an input laser beam (18); - an optical assembly (20) according to any one of claims 1 to 12 for converting said input laser beam (18) into said linear output beam (12).

14. 1. A method for controlling a displacement device (54) with respect to one of two lens arrays (38, 40) in an optical assembly (20) for converting an input laser beam (18) into a linear output beam (12) propagating along a propagation direction (z) and having a linear beam cross-section with non-zero intensity expanded along a linear direction (x) at a working plane (14), the optical assembly (20) comprising: a shaping optical system (22) having an input aperture (34) into which the input laser beam (18) can be incident, and an output aperture (36), the shaping optical system (22) being configured such that the input laser beam (18) incident through the input aperture (34) is transformed into a beam packet (24) having a number of beam segments which exits through the output aperture (36); a homogenization optics (26) and at least one redirecting lens means (30), the homogenization optics (26) being configured to mix various beam segments of the beam packet (24) along the linear direction (x), the redirecting lens means (30) being configured to superimpose the mixed beam segments (28) onto the linear output beam (12), the homogenization optics (26) comprising a first lens array (38) and a second lens array (40) arranged in a beam path downstream of the first lens array (38); a displacement device (54) having an actuator (56) and a control device (58), The method includes a step of controlling the displacement device (54) using the control device (58) according to a primary control mode (60) to displace the second lens array (40) relative to the first lens array (38), characterized in that during the controlling, a target frequency and / or a target amplitude of the displacement movement of the second lens array (40) set by the primary control mode (60) is adapted by at least one auxiliary control mode (62, 64, 66) to homogenize the linear output beam (12).

15. - by means of a first auxiliary control mode (62), the change in the target frequency set by the main control mode (60) is carried out on the basis of a continuous target frequency change (63) over time, - adapting the target amplitude set by the primary control mode (60) based on an allocation rule (65) by means of a second auxiliary control mode (64) such that the actuator (56) executes an adapted target amplitude realizing an actual amplitude of the displacement of the second lens array (40), the actual amplitude being closer to the target amplitude set by the primary control mode (60) than when executing the target amplitude set by the primary control mode (60); and / or The method according to claim 14, wherein by means of a third auxiliary control mode (66), the target amplitude set by the main control mode (60) is set with respect to a zero crossing of the displacement movement of the second lens array (40).

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