Adaptive Laser Beam Shaping

Abstract

A method for adaptively splitting a coherent primary light beam, comprising producing a desired far-field distribution by phase modulating the primary light beam with a Spatial Light Modulator (SLM), the primary coherent light beam being directed to reflect on a display element of the spatial light modulator, thereby avoiding any moving elements to shape the primary coherent light beam, extracting from the primary light beam, after it has passed the spatial light modulator, a monitoring beam and a main beam, measuring the monitoring beam with a camera, directing the desired far-field distribution in the monitoring beam on a sensor surface of the camera. In a first option, the method comprises guiding the primary beam through a first focusing element (L1) that is configured to focus the far-field distribution onto a focusing plane of the first focusing element as a real output distribution, and focusing the far-field distribution in the monitoring beam onto the sensor surface of the camera by means of the first focusing element. In a second option, the method comprises guiding the monitoring beam through a second focusing element (L2) that is configured to focus the far-field distribution on the sensor surface of the camera. For either the first or the second option, the method further comprises adjusting a dynamic range of the camera using a variable intensity regulator to control the intensity of the incoming monitoring beam as a function of the far-field distribution, and configuring a closed loop to enable a phase calculation for the display element of the spatial light modulator, whereby an output signal from the camera is input into the closed loop for a plurality of iterations of a phase-calculation algorithm performed by a controller, wherein in the first option, the first focusing element is used, excluding the second focusing element, and in the second option, the second focusing element is used, excluding the first focusing element.

Claims

1-21. (canceled)

22: A method for adaptively splitting an at least partially coherent primary light beam by a spatial light modulator, comprising: providing the at least partially coherent primary light beam by a collimated laser beam from a nanosecond laser, a picosecond laser, or a femtosecond laser; producing a desired far-field distribution, that is independent on a profile of the coherent primary light beam, by phase modulating the primary light beam with the spatial light modulator, the primary coherent light beam directed to reflect on a display element of the spatial light modulator to avoid a moving element to shape the primary coherent light beam; extracting from the primary light beam, after the primary light beam has passed the spatial light modulator, a monitoring beam and a main beam; directing a far-field distribution produced by the spatial light modulator in the monitoring beam onto a sensor surface of a camera and measuring the monitoring beam with the camera; guiding the primary beam through a focusing element that is configured to generate the far-field distribution in the main beam onto a focusing plane of the focusing element as a real output distribution; projecting the far-field distribution in the monitoring beam onto the sensor surface by the focusing element; matching a dynamic range of the camera by using a variable intensity regulator to control the intensity of the incoming monitoring beam as a function of the desired far-field distribution, independent of the average power of the main beam; and configuring a closed loop to enable a phase calculation for the display element of the spatial light modulator, an output signal from the camera is input into the closed loop for a plurality of iterations of a phase-calculation algorithm performed by a controller device.

23: The method of claim 22, further comprising: structuring a solid surface with the main beam; and controlling the structuring by setting the spatial light modulator to obtain a determined profile for the primary light beam.

24: The method of claim 23, further comprising: adjusting the focusing plane of the focusing element for the step of structuring the solid surface such that the focusing plane corresponds to the solid surface.

25: The method of claim 23, further comprising: adjusting the focusing plane of the focusing element to an intermediate plane; and imaging the intermediate plane by a projecting optical set-up in a reduced scale onto the solid surface.

26: The method of claim 23, wherein the solid surface includes at least one of a metal, a diamond, a sapphire, a glass, a plastic, a composite material, and leather.

27: The method of claim 23, wherein the solid surface is a part of a working tool.

28: The method of claim 27, wherein the working tool includes at least one of an embossing roller, a stamping device, a metal fool, a wristwatch component, a jewelry part, and a packaging component.

29: The method of claim 22, wherein the step of extracting includes a beam-splitting element, the method further comprising: integrating the beam-splitting element, the focusing element, the spatial light modulator, the variable intensity regulator, and the camera into a single enclosure, the single enclosure is configured to be a component placed in the primary coherent light beam; and adjusting the variable intensity regulator by the controller device.

30: A method for adaptively splitting an at least partially coherent primary light beam by a spatial light modulator, comprising: providing the at least partially coherent primary light beam by a collimated laser beam from a nanosecond laser, a picosecond laser, or a femtosecond laser; producing a desired far-field distribution, that is independent on a profile of the coherent primary light beam, by phase modulating the primary light beam with the spatial light modulator, the primary coherent light beam directed to reflect on a display element of the spatial light modulator to avoid a moving element to shape the primary coherent light beam; extracting from the primary light beam, after the primary light beam has passed the spatial light modulator, a monitoring beam and a main beam; directing a far-field distribution produced by the spatial light modulator in the monitoring beam onto a sensor surface of a camera and measuring the monitoring beam with the camera; guiding the monitoring beam through a focusing element that is configured to project the far-field distribution onto the sensor surface; matching a dynamic range of the camera by using a variable intensity regulator to control the intensity of the incoming monitoring beam as a function of the desired far-field distribution, independent of the average power of the main beam; and configuring a closed loop to enable a phase calculation for the display element of the spatial light modulator, an output signal from the camera is input into the closed loop for a plurality of iterations of a phase-calculation algorithm performed by a controller device.

31: The method of claim 30, further comprising: structuring a solid surface with the main beam; and controlling the structuring by setting the spatial light modulator to obtain a determined profile for the primary light beam.

32: The method of claim 31, wherein the step of structuring includes applying the far-field distribution, for obtaining the structures on the solid surface, by projecting the far-field distribution by a focusing optical set-up onto the solid surface.

33: The method of claim 30, wherein the step of extracting includes a beam-splitting element, the method further comprising: integrating the beam-splitting element, the focusing elements, the spatial light modulator, the variable intensity regulator, and the camera into a single enclosure, the single enclosure is configured to be a component placed in the primary coherent light beam; and adjusting the variable intensity regulator by the controller device.

34: The method of claim 30, further comprising: splitting the primary light beam into a plurality of partial main beams by the spatial light modulator; individually adjusting a number of the plurality of partial main beams, angles of separation between each of the plurality of partial main beams after the plurality of partial main beams leaves the display element of the spatial light modulator, and intensities of each of the plurality of partial main beams among each other by phase control, the intensities of the plurality of partial main beams among each other is controlled by the controller device that is further configured to control an individual generation for each of the plurality of partial main beams, the spatial light modulator and the primary light beam; and structuring the solid surface with the plurality of partial main beams.

35: The method of claim 31, wherein the solid surface includes at least one of a metal, a diamond, a sapphire, a glass, a plastic, a composite material, and leather.

36: The method of claim 31, wherein the solid surface is a part of a working tool.

37: The method of claim 36, wherein the working tool includes at least one of an embossing roller, a stamping device, a metal fool, a wristwatch component, a jewelry part, and a packaging component.

38: A device configured for an adaptive splitting of an at least partially coherent primary light beam by a spatial light modulator, the at least partially coherent primary light beam originating from a collimated laser beam from a nanosecond laser, a picosecond laser, or a femtosecond laser, the device comprising: the spatial light modulator configured to produce a desired far-field distribution, which is not dependent on the profile of the coherent primary light beam, by phase modulation of the at least partially primary light beam, further configured to obtain the primary light beam from a display element of the spatial light modulator, to avoid a moving element to shape the primary light beam; a beam splitting element positioned in the at least partially coherent primary light beam after the at least partially coherent primary light beam has passed the spatial light modulator, and configured to extract from the primary light beam, a monitoring beam and a main beam; a camera positioned in the monitoring beam, the camera including a sensor surface configured to measure a far-field distribution produced by the spatial light modulator in the monitoring beam, a first focusing element configured to, project the far-field distribution produced by the spatial light modulator in the monitoring beam onto the sensor surface, and guide the primary beam and generate the far-field distribution in the main beam onto a focusing plane of the first focusing element as a real output distribution; a variable intensity regulator positioned in the monitoring beam in front of the camera, and configured to match a dynamic range of the camera by control of the intensity of the incoming monitoring beam as a function of the desired far field distribution, independent of the average power of the main beam; and a closed-loop set-up configured to enable a phase calculation for the display element of the spatial light modulator, including a controller device connected to the camera to receive an output signal, and configured to use the output signal for a plurality of iterations of a phase-calculation algorithm performed in the controller device.

39: The device according to claim 38, further comprising: a second focusing element positioned in the monitoring beam and configured to project the far-field distribution produced by the spatial light modulator onto the sensor surface.

40: The device according to claim 39, further comprising: a switch configured to switch between use of the first focusing element without using the second focusing element, and use of the second focusing element without using the first focusing element.

41: The device of claim 38, wherein the device is configured for machining of a solid surface and further configured to position the solid surface in the main beam, wherein the machining of the solid surface results from at least a setting of the spatial light modulator for producing a determined profile for the primary light beam.

42: The device of claim 41, wherein when the switch is configured to use of the first focusing element without using the second focusing element, the focusing plane of the first focusing element is configured to correspond to the solid surface.

43: The device of claim 41, further comprising: an imaging optical set-up, the first focusing element being positioned such that a focusing plane of the first focusing element corresponds to an intermediate plane, and the imaging optical configured to image the intermediate plane in a reduced scale onto the solid surface.

44: The device of claim 41, further comprising a focusing optical set-up configured to project the desired far field distribution of the main beam onto the solid surface for the machining.

45: The device of claim 40, further comprising: a single enclosure configured to integrate the beam-splitting element, the first and second focusing elements, the spatial light modulator, the variable intensity regulator, and the camera, wherein the single enclosure is configured to be a component to be placed into the primary light beam, wherein the controller device is configured to control the switch to switch between the first configuration option and the second configuration option, and to adjust the variable intensity regulator.

46: The device of claim 41, wherein the spatial light modulator is enabled to split the primary light beam into a plurality of partial main beams, and to individually adjust a number of the plurality of partial main beams, angles of separation between each of the plurality of partial main beams after the plurality of partial main beams leaves the display element of the spatial light modulator, and intensities of the plurality of partial main beams among each other by phase control, wherein the controller device is further configured to control the intensities of each of the plurality of partial main beams among each other, by control of spatial physical properties for each of the plurality of partial main beams, wherein the spatial physical properties are at least one of phase and amplitude, the spatial light modulator and the primary light beam, and wherein the controller device is further configured to position the solid surface in the plurality of main beams.

47: The device of claim 41, wherein the solid surface is a surface of an embossing roller and the controller device is further configured to position the surface of the embossing roller in the main beam.

48: The device of claim 41, wherein the solid surface includes at least one of a metal, a diamond, a sapphire, a glass, a plastic, a composite material, and leather.

49: The device of claim 41, wherein the solid surface is a part of a working tool.

50: The device of claim 49, wherein the working tool includes at least one of an embossing roller, a stamping device, a metal tool, a wristwatch component, a jewelry part, a packaging component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention will be understood better through the detailed description of preferred embodiments, and in reference to the figures, wherein

[0052] FIG. 1 shows a SLM module configuration according to an example embodiment of the invention;

[0053] FIG. 2 shows a further SLM module configuration according to an example embodiment of the invention;

[0054] FIG. 3 shows an alternative construction of the SLM module in which a mirror is used, according to an example embodiment of the invention;

[0055] FIG. 4 shows a further alternative construction of the SLM module in which a focusing element is positioned in front of an SLM display, according to an example embodiment of the invention;

[0056] FIG. 5 shows a further alternative construction of the SLM module in which the focusing element is positioned before the SLM display and only one mirror is included, according to an example embodiment of the invention;

[0057] FIG. 6 shows a further alternative construction of the SLM module in which the focusing element is positioned after a semi-transparent mirror according to an example embodiment of the invention;

[0058] FIG. 7 shows a further alternative construction of the SLM module in which the focusing element is positioned after the semi-transparent mirror, and a mirror is solely included according to an example embodiment of the invention;

[0059] FIG. 8 shows an SLM module as a component of a micro-structuring device according to an example embodiment of the invention;

[0060] FIG. 9 shows another SLM module as a component of a micro-structuring device according to an example embodiment of the invention;

[0061] FIG. 10 shows an example use according to the invention; in which a parallel structuring of grooves is made with a comparatively small offset of the pulses;

[0062] FIG. 11 shows another SLM module as a controllable beam splitter according to an example embodiment of the invention;

[0063] FIG. 12 shows a further example use according to the invention, in which the parallel structuring of grooves is made with a comparatively large offset of the pulses;

[0064] FIG. 13 shows a further example uses according to the invention; in which profiles with a 2-dimensional output distribution are structured;

[0065] FIGS. 14a and 14b show further example uses according to the invention for surface profiles perpendicular to a direction of propagation, during structuring with slanted 2-dimensional output distribution;

[0066] FIGS. 15a and 15b show further example uses according to the invention for surface profiles at a structuring with comparatively small pulse offset;

[0067] FIGS. 16a and 16b show further example uses according to the invention for surface profiles at a structuring with comparatively large pulse offset; and

[0068] FIG. 17 shows an example of a device configured for machining a surface of an embossing roller.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Goal of the Invention

[0069] It is a goal of the invention to make it easier for a user to obtain beam shaping, and more particularly beam splitting of laser radiation. The invention, herein after named the “SLM module”, in a further aim, provides a device and a method that may be integrated in any optical path, and offers a comparatively high degree of compactness and individual functionality, independent of the place of use. Another aim of the invention is to allow a splitting of any type of collimated primary beam (laser source) with a comparatively high precision, independent of beam profile, phase position, bandwidth/pulse duration and laser power.

[0070] One advantage that derives from the invention is that any limitation of the SLM module may be anticipated through the understanding of the properties of its core element, the SLM display as such. Another advantage lies in the fact that the beam splitting may be implemented with very little losses only. Hence, the incoming radiation should be purely phase modulated, although a simultaneous or sole amplitude modulation would also produce this type of functionality. A further advantage is that the invention enables to switch back and forth between a real output distribution in a focal plane of a lens, i.e., the Fourier plane and a far field distribution, i.e., the diffraction image that occurs at infinite distance. A further advantage is that a comparatively high degree of precision may be achieved in the produced output distribution as well as the beam-power distribution from one partial beam to another, because the invention utilizes a closed-loop approach for the calculation of the phase values that is not dependent on the input profile or the primary beam profile of the laser source, respectively.

[0071] The inventive SLM module allows a more efficient use of the laser power by enabling parallel micro machining and machining of solid surfaces with a plurality of beams, too. This may be at a working station by means of an output optics used in common, or at a plurality of systems simultaneously, whereby each of the plurality of systems makes use of a split primary beam that is shared by all machining systems. The parallel machining may reduce the duration of the process for machining larger surface and volumes, linearly with the number of partial beams. Mien using a shared output optics for all partial beams, it becomes possible to produce groves, grating structure and other highly repetitive patterns with increased speed. The SLM module according to the invention enables to achieve a simultaneous and precise machining with a large number of partial beams, for example 1000 beams or more.

[0072] Based on the above-mentioned goals and properties of the SLM module according the invention, the production performance of a laser micro machining/structuring device may be increased drastically while still keeping a compact footprint and highly stable operation condition. Therefore, this will allow for industrially applicable reductions in production cost and lead time.

Structure and Function of Iterative Fourier-Transformation Algorithm (IFTA)—Closed-Loop (CL) Module

Prerequisites for the Input Beam

[0073] The primary laser beam used throughout this invention must respond to a number of criteria in order to enable the functionality of the SLM module. A first criterion is that the primary beam at the input of the SLM module is collimated or parallelized. The person skilled in the art is aware of the fact that the beam for wave-optics elements and optical gratings must have a coherence length in the order of the grating period. Since ultra-short pulsed radiation is used in the context of this invention, the time-dependent coherence length may also be very short, such as for example only a few micrometers.

[0074] The person skilled in the art is further also aware, that when a SLM display of the SLM module comprises an element based on liquid crystals on Silicon (LCoS) technology, the input radiation must inherently obey to determined polarization states relative to an orientation of the SLM display. This can be adjusted and taken care of by means of commercially available structural elements positioned in front of the SLM module. This is the reason why this will not be discussed further in the present document. It is also generally known that LCoS technology has a strongly wavelength-dependent behavior.

[0075] Also generally known is the fact that a user of the SLM module may select and adjust the beam-diameter, the mean optical power or a pulse energy, as long as the user remains below physical destruction limit of any component found in the SLM module.

Structure of the SLM Module

[0076] As will become apparent from the following description, the inventive method and device enable the user, starting from a primary input beam that fulfills the above-mentioned criteria, to split this primary input beam into an arbitrary number of output beams, which may be put to use at the user's choice. The output beams may be controlled in their spatial and intensity distribution in a time-dependent manner by the user or a control process. The invention further enables to use either a real intermediate distribution or merely an angular distribution, depending on the desired machining task. The invention enables to achieve this without any precise knowledge of the profile of the primary input beam or its coherence length. The invention requires no other prerequisites for the primary input beam than those described herein above. Any deviations occurring in the output main beam due to the lack of information may be compensated by means of the closed-loop algorithm, which is used to optimize the output distribution.

[0077] The invention enables a so-called “Black-Box-Optics” that may be integrated into any kind of optical paths for micro machining.

[0078] FIG. 1 shows an SLM-module configuration according to an example embodiment of the invention, which allows to enable the features of the invention as described herein above. A mirror M1 directs radiation from a primary beam—originating from a laser source not shown in FIG. 1 but suggested by the reference 100 and the corresponding arrow in the drawing—in a comparatively tight angle on a reflecting SLM head 101. The SLM head 101 is considered a central element of the SLM module. The SLM head 101 comprises a SLM display—not explicitly referenced in FIG. 1—which is used to apply beam-shaping phase values to the incoming primary laser beam. The SLM display may be, e.g., realized as an LCoS—also not explicitly referenced in FIG. 1. As is known to the person skilled in the art, LCoS displays cause effects that influence a polarization of the radiation and thereby influence the efficiency of diffraction. To counter this effect, the SLM module comprises an additional polarizing beam splitter 102 placed after the SLM display, which filters out falsely polarized and/or non-diffracted radiation. The SLM module further comprise a semi-transparent extraction mirror M2. The polarizing beam splitter 102 is installed in the optical path in front of the extraction mirror M2, thereby making sure that a distribution after reflection on the SLM display appears the same way on a CCD camera 104 positioned in an optical path of a monitoring beam coupled out from the primary beam by the semi-transparent mirror M2, and in the Fourier plane 103 where the real output distribution occurs, or infinity, depending on the case. The semi-transparent mirror M2 may be realized, e.g., as a dielectric reflection-coated mirror with plane-parallel substrate that is transparent for the wavelength of the primary beam. Preferably, mirror M2 has a surface quality of industry standard for transparent optics and glass surfaces. In this manner, the monitoring extracted/coupled-out at the mirror M2 may be used for beam analysis without having excessive power losses despite the comparatively high beam power utilized in micro machining environments. In the optical path in front of the CCD camera 104, a variable intensity regulator 105 is configured for adjusting the intensities to match the dynamic range of the CCD camera 104 so that it can be used in an optimized manner and independent of the average power of the primary beam, the output distribution and/or the beam-splitting ratios. The variable intensity regulator 105 may for example be realized as an ND (Neutral Density) filter.

[0079] While in the present detailed description the SLM head 101 is used in a mode in which it reflects the radiation from the primary beam, in a further preferred embodiment it is possible to have a SLM head which works as a transmitter for the primary beam.

[0080] A picture recorded by the CCD camera 104 must always be the Fourier transformation of the input distribution. For this reason, the sensor surface (not represented in FIG. 1) of the CCD camera 104 must be located in the focal plane of a focusing optics element, such as, e.g., a first focusing element L1 and a second focusing element L2. In the example of FIG. 1, the first focusing element L1 and the second focusing element L2 are never placed together, i.e., simultaneously, in the optical path between the SLM head 101 and the CCD camera 104. Preferably, the CCD camera 104 is centered on the optical axis of the monitoring beam, which was extracted by the semi-transparent mirror M2.

[0081] The CCD camera 104 enables to obtain a measure of the output distribution, which in turn may be used as an input into an iterative Fourier-Transformation-Algorithm (IFTA)-based closed-loop control to optimize the phase distribution generated by the SLM head 101. As mentioned before, this requires measuring the output distribution with the CCD camera 104 and feed the algorithm executed on the controller CPU 106 as part of the boundary conditions of the IFTA. The IFTA algorithm will not be discussed here in more detail, because it may be found in dedicated literature from prior art. The calculated phase values are applied subsequently to the SLM display.

Configuration of the SLM Module

[0082] The SLM module may adopt any one of two hardware configurations to enable a switch between angular distribution and real intermediate distribution. A switching between both of these configurations, as well as a change of filter settings for the variable intensity regulator may be realized manually or with automated switching means.

[0083] In a first hardware configuration, called configuration 1 herein, and as represented in FIG. 1, the first focusing element L1 is placed in the optical path. L1 focuses the laser radiation on the sensor surface of the CCD camera 104, which is placed at a distance of the focal length f(L1) of L1 and behind the semi-transparent mirror M2. Furthermore, the CCD camera 104 is placed in a plane of the main output beam perpendicular to the propagation direction of the main output beam, i.e., the mask plane. In the example of FIG. 1, the first focusing element L1 is positioned in front of the polarizing beam splitter 102. In an alternative not illustrated in FIG. 1, the first focusing element L1 may be positioned behind the polarizing beam splitter 102. In the configuration of FIG. 1, the second focusing element L2, which as a focal length f(L2), is not positioned into any optical path. The distribution recorded by the CCD camera 104 is identical and mirrored as compared to the mask plane. Configuration 1 enables that the main beam that is reflected from the mirror M2, is focused in a real intermediate distribution.

[0084] Now looking at FIG. 2, it represents a configuration 2, which is in most respects identical to configuration 1 from FIG. 1, except that the second focusing element L2 is positioned into the optical path of the monitoring beam extracted through the semi-transparent mirror M2. The sensor surface (also not shown in FIG. 2) of the CCD camera 104 is now placed in the focal plane of the second focusing element L2, i.e., at the distance of the focal length f(L2) of the focusing element L2. Hence, for this configuration 2, L1 is not positioned into any optical path. Configuration 2 enables that the main output beam, which is reflected at the mirror M2 is not focused into an intermediate distribution. The target distribution of the diffraction grating is formed at infinity as an angular distribution. The primary input beam is split into a plurality of partial main beams.

Alternative Constructions

[0085] The invention may be realized through a variety of alternative constructions that all provide the same functionality. Each of the variety of alternative constructions may be considered to possess various disadvantages and advantages as compared to configurations 1 and 2.

[0086] FIG. 3 shows an alternative construction in which only one dielectric mirror M is used—the mirror M1 from FIGS. 1 and 2 is not used here. The dielectric mirror M must comply with all requirements as previously presented. The positions for the first focusing element L1 and the second focusing element L2 may be identical to those discussed in the frame of FIGS. 1 and 2—immediately before or behind the dielectric mirror M. One advantage in the present construction as compared to that of FIG. 1 is that it is inherently more compact. However, the angle between incoming beam and the outgoing beam is imposed. The construction of FIG. 3 is in a similar mode as configuration 2—for an easier reading, we will say that it is in configuration 2. In order to switch to configuration 1, the first focusing element L1 must be positioned into the optical path and the second focusing element L2 must be removed from the optical path. Arrows next to the elements L1 and L2 symbolize this.

[0087] FIG. 4 shows a further alternative construction in configuration 1. In this alternative construction, the first focusing element L1 is positioned at a distance a in front of the SLM display, and similar as in FIG. 1, two mirrors M1 and M2 are used. Both focusing elements L1 and L2 are movable, as symbolized by arrows next to the elements. There is no obvious advantage with this alternative construction. One potential difference as compared to the one of FIG. 1, is that the focal length for the first focusing element L1, represented as f(L1)=a b within the figure, must be comparatively larger than for example in FIG. 1, which in turn reduces a resolution of the output distribution.

[0088] FIG. 5 shows a similar construction as that of FIG. 4, but in the configuration 2 setup, whereby again only 1 mirror M is used. The same properties as noted for FIG. 3 apply here also: the device can be made more compact but on the other hand, one limits the angles for coupling and decoupling of the laser beam into and out of the SLM module.

[0089] FIG. 6 shows a construction in configuration 2, in which a third focusing element L3 (for example a lens) having a focal length f(L3) is located behind the semi-transparent mirror M2. To improve readability, L1 is not shown in FIG. 6 because it is removed from the optical path in this setup. The second focusing element L2 may be inserted into the optical path as symbolized by arrows next to the second focusing element L2. One advantage is that the second focusing element L2 may be fixed into the optical path, i.e., it does not need to be moved anymore when switching between configurations by moving L3.

[0090] FIG. 7 shows a construction similar to that of FIG. 6, but with a single mirror M to render the device more compact.

Losses in the Optical Path

[0091] One of the advantages of the inventive SLM module is to enable a beam shaping with virtually no losses. Consequently, no absorption masks or scatter masks need to be used to obtain the desired output distribution. The beam shaping is done exclusively by means of the phase distribution applied to the SLM head. However, the person skilled in the art will acknowledge that for real life optical paths, there will inevitably occur small losses to a laser beam.

[0092] When using ideal optical elements, there will only be scattering losses at the diffraction grating of the SLM, and this only for higher diffraction orders, since the sought-after target distribution is located exclusively in the first order of diffraction.

Areas of Use and Possibilities of Applications

Parallel Micro-Structuring/Parallel Structuring

[0093] The inventive method and device may be integrated into any optical path, as long as there is enough physical space to do so and the afore-mentioned conditions for the laser-beam are fulfilled. FIG. 8 shows an example of such a system for micro structuring by projection exposure, wherein the mask plane in the optical path is replaced by the real output distribution 103 of an SLM module 800 configured in configuration 1. The SLM module 800 is fed at its input with a primary laser beam 801 output from a laser source 802. The real output distribution 103 is projected onto a work piece 803 by means of a microscope 804 of a micro-machining head 805, also called means for parallel micro structuring. The work piece 803 is mounted on a positioning stage 806 that is configured to move the work piece 803 at least in a plane X-Y perpendicular to the direction of the projected light beam. A second camera 807 is configured to monitor the main beam that is projected onto the work piece 803 and may also serve as part of an autofocusing device. The person skilled in the art is aware of the manner in which optical systems function and their parameters for projection imaging. This knowledge of the person skilled in the art essentially provides the parameters of the applicable phase distribution and do not have any limitative effect on the SLM module 800. The controller CPU 106 is further configured to control the positioning of the focusing elements L1 and L″, as well as the variable intensity regulator 105.

[0094] FIG. 9 shows an example of an integration of the SLM module 800 in a system for focused machining. In this particular case, the SLM module 800 is configured in configuration 2. It allows that the number of partial main beams that can be used for laser machining may be increased. Ideally, for most optical paths and optics to be used in such a system, the SLM module 800 should be located as close as possible to the final optics; in the present example this would be the micro-machining head 805, in order to avoid any restriction caused by its aperture.

[0095] The increased number of focal points has the beneficial effect that machining speeds of the laser process that are based on focused beams increase in proportion to the number of partial main output beams. In addition, it also allows making a more optimal use of the laser power. The switching between the partial beam distribution and the focal distribution may occur at a speed corresponding with the display refresh rate of the SLM head 101 and involves no moving part at all. As the person skilled in the art is aware of, phase modulation also allows correcting Zernike modes and in turn, this will increase the focus quality. If the erroneous phase position of the primary beam is also known, it is possible to improve the beam quality of all partial main beams by means of the SLM module 800. The SLM module 800 does not influence imaging scaling factors as well as beam diameters otherwise.

Examples of Structuring for Parallel Micro Machining

[0096] Parallel micro structuring by means of many partial main beams with individually controllable pulse energy or beam power offers similar possibilities of structuring as with individual beams. FIG. 10 schematically shows a beam offset dx for a pulsed primary beam that is split into n×m partial output beams, p1, p2, p3, etc. denominate the pulse sequence in time. The work piece is moved along the x-axis of the rectangular distribution, whereby an offset dx occurs between two laser pulses. In this manner, it is possible to draw a set of n lines, whereby each line is irradiated multiple times, normally in a slightly overlapping manner. The resulting profile of lines have a constant depth along a line in direction v and the set of lines has a distribution f(x) of maximal depths, as shown in FIG. 15b.

[0097] A further possibility to work with such a short pulse-offset is a so-called surface removal, as shown in FIG. 15a. In this case, the work piece is moved in respect to the laser according to a feed v1 in such a manner that a surface is covered that is limited by neighboring partial beams. In this manner it becomes possible to produce 2.5D surface topographies.

[0098] A further potential approach in parallel micro structuring consists in spacing the partial beams by a distance of dx, as shown in FIG. 12. The distance covered in time between each pulse will be slightly more than dx so that an effective distance between each pulse will result in dn. In the specific example shown in FIG. 12, m=5 pulses will be placed between two partial beams spaced with dx. Using this machining strategy, the effective distance between each pulse can reduced. The structuring time for simple gratings can be decreased significantly by using optimized ratios between dx, dn, and m.

[0099] An even further possibility is to slant a periodic output beam distribution as compared to the feed by an angle alpha as illustrated in FIG. 13. In this manner, each partial beam may produce a line with constant removal depth or illumination dose, and depending on the angle alpha, the individual illuminated traces may also overlap perpendicularly to the feed v2. The apparent distance dy′ between pulses increases with an increase in the slanting angle alpha. By designing the spatial distribution of the partial beams in x and y direction by dx and dy, respectively, one can generate an apparent intensity distribution along one dimension. Hence, it becomes possible to produce any type of section profile f(x) in a single pass—see also FIGS. 14a and 14b. If all lines in the output distribution are identical among themselves, then n identical profiles are produced simultaneously—see FIG. 14a.

[0100] Making use of a pulsed beam for working, a structuring along the partial beam may allow attributing a periodic function f(x) to the removal-depth or illumination intensity. To this end the feed, the number of partial main beams along the line and their distance must have a fixed ratio. FIG. 16a shows a profile A along the left line in direction v3, which is illustrated in cross-section view in FIG. 16b. The pulse energy of the partial beams along this line is decreased continuously.

Structuring of an Embossing Roller Surface

[0101] FIG. 17 illustrates an example device that may be used to structure an embossing pattern 1700 on a working tool, more specifically an embossing roller surface. The SLM module 800 inputs the primary light beam, i.e., the collimated and at least partially coherent light source from the laser source 802, and directs at its output the main beam on the surface of the embossing roller. Various options are available to adjust the relative position between the SLM module 800 and the embossing roller. In the illustrated example, the SLM module 800 may be moved according to the indicated x-direction, but the embossing roller may also be rotated by a motor 1701 according to the indicated circular arrows. The controller 106 is further configured to adjust the relative position between the SLM module 800 and the embossing roller, thereby controlling the SLM module 800, the laser source 802 and the motor 1701 as appropriate, in order to achieve a structuring of the embossing roller surface with the embossing pattern 1700.

Beam Splitting

[0102] FIG. 11 illustrates the functional principle of the beam splitting/separation functionality. The SLM module 800 in configuration 2 is positioned at the output of a laser-beam source 802. For the primary laser beam 801, the previously mentioned restrictions still apply. The primary laser beam 801 is diffracted at a phase grating which has been calculated as described into m partial main beams and then deviated to m differently oriented mirrors M1-Mm. These mirrors subsequently reflect the respective partial beams to m different working-, exposure- and/or measuring-stations or beam dumps (unit 1-unit m). The power distribution, the number and the exit angles of the partial beams among themselves may be controlled over time by switching the phase values at the SLM head 101, This allows to use the laser power more efficiently and to use only one single laser source for different tasks. In addition, the SLM module 800 as already mentioned above allows correcting erroneous Zernike modes and may therefore contribute to improve the beam quality of every partial beams.

LITERATURE

[0103]

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