RU2796474C2 - Adaptive laser beam formation - Google Patents

Abstract

FIELD: adaptive generation of laser beams.

SUBSTANCE: method and device for implementing adaptive splitting of a partially coherent light beam by means of a spatial light modulator (SLM) consists in creating a partially coherent primary light beam from a collimated laser beam, creating a field distribution in the far zone, modulating in the SLM phase, directing for reflections on the SLM display element, preventing the formation of a primary coherent light beam by any moving element, removing from the primary light beam, after the SLM, the control and main beams are directed to the field distribution in the far zone, to the shooting camera and the control beam is measured by the camera, while ensure compliance with the dynamic range of the camera by means of a variable intensity controller to control the intensity of the pilot beam, regardless of the average power of the specified at least one main beam, configure a closed loop for phase calculation, in which the output signal from the camera is introduced into a closed loop for multiple iterations of the phase calculation algorithm, executed by the controller.

EFFECT: enhancement of laser system functionality.

21 cl, 17 dwg

Description

The technical field to which the invention belongs

[1] The invention relates to the field of adaptive formation of a beam of coherent or partially coherent radiation with parallel direct structuring, microstructuring and beam splitting, as well as for machine processing of materials in industry, using a phase modulating spatial light modulator (PMS) for beam formation.

State of the art

[2] Below are a number of publications describing the prior art of the invention.

[3] Methods for adaptive formation of a laser beam by means of spatial light modulators (SLMs) are disclosed in a relatively small number of professional and scientific publications. One of the most notable publications in this area is [SIL13] (see the References section at the end of the description) by Matti Silvennoinen from 2014. The method of action disclosed in it is characterized by the following:

• application of ultrashort radiation pulses (pulse width <500 ps);

• application of phase-modulating PMS for beam formation;

• direct structuring by displaying a set of partial beams focused in an intermediate plane (Fourier plane); And

• application of a closed loop to iteratively determine the phase and display it on the PMS display, wherein the closed loop (3K) algorithm is configured to measure the distribution of the output beam in each iteration cycle by means of a camera and re-enter it, as input, into the iterative phase detection algorithm. calculation. These algorithms will be referred to in this document by the abbreviation "3K".

[4] The disclosed mode of operation requires that the output distribution or profile of the primary laser beam be known at the location of the SLM display. Its measurement requires at least additional efforts and time, as well as changes in the optical scheme of the beam path, which is a disadvantage from a production point of view.

[5] The nature of the disclosed scheme is not monolithic enough, namely, partial beam extraction for measurement by a shooting camera, which is essential for 3K, is part of the final optical group and occurs at the last inclined mirror. Therefore, the optical design and the method of its operation are not flexible enough. Adaptive beam shaping can only be implemented for the entire microstructuring system, but not for the beam as such. Unfortunately, in the case of industrial applications, this characteristic is a real problem that is difficult to overcome, since the concept of the system must be adapted to each specific machining task and stop production for this period.

[6] In addition, the system does not use a transform lens to create an intermediate distribution, which, in turn, can be projected downscaled. The intermediate distribution is obtained by adding spherical phase components to the original phase distribution reproduced on the SLM and acts as a virtual lens. This provides the advantage that the non-diffracted components of the beam will not be collected in zero order, but will be distributed throughout the output distribution, whereby they are eclipsed by other components - at least in most cases of intensity distribution. The disadvantage of this method is that some information may be lost in the phase representation; see FIG. 3A in [SIL13]. This is due to the increase in spatial frequencies in the phase representation towards the boundaries, due to the spherical term, until they exceed the resolution of the display of the ICP. This also places a lower limit on the focal length of these spherical terms, which is approximately 500 mm for a pixel size of 20×20 μm ² . Up to this lower focal length limit, the SLM display contains no useful phase information, and therefore zero order content output is increased. This is a contradiction with the initially indicated advantage. In addition, the loss of information in the direction of the boundaries can be the cause of disordered diffraction of laser radiation, when the diffraction of radiation occurs at angles not determined by the initial grating period, and cannot be corrected using 3K.

[7] [BEC11] discloses another development, also a 3K-based method for beam splitting. The method is called "Modified iterative Fourier-transformation Algorithm (MIFTA)". The method can be described as follows:

• extract part of the beam after the conversion lens by means of a beam splitter with a low splitting ratio, then measure it by means of a charge coupled device (CCD) camera and use it as input to the iteration cycle of the MIAPF ;

• the applied scheme is monolithic and provides the possibility of splitting the beam into separate subbeams independent of the laser scheme as such; And

• beams of the obtained profiles are projected on a reduced scale onto the surface of the substrate to achieve direct microstructuring.

[8] In this scheme, only nanosecond laser radiation is used. The publication is silent on whether the disclosed mode of operation is also applicable to ultrashort pulsed laser radiation. Ultrashort-pulse laser radiation, i.e. Pico- and femtosecond laser radiation may behave differently on optical gratings due to the shorter time-dependent coherence length and larger bandwidth when diffracted by optical gratings.

[9] The display of the applied PMS is controlled in a binary way, which results in liquid crystals oscillating around their axis of rotation, in connection with which the phase position of the laser changes over time, which, in turn, affects the result of machining. According to the publication, the solution to this problem consists in performing a plurality of impacts and shifting the phase position in the interval between impacts perpendicular to the direction of propagation of the laser beam. This solution will significantly increase the processing time, since the range of the SLM frame rate is only a few tens of Hz, which significantly narrows the scope of industrial application due to an increase in the duration of structuring by several orders of magnitude, making structuring by radiation impossible.

[10] This scheme can only be used to obtain real intermediate distributions due to the presence of only one transform lens. Physical separation of each of the plurality of partial main beams is not possible due to the presence of a single conversion lens. If the single conversion lens were removed, it would be impossible to track the generated output distribution at the same time.

[11] In papers [KUA08], [KUA09], [KUA09_2], and [JIN15], researchers working with Zhen Kuang and Walter Perrie disclose several applications of phase modulating SLMs for parallel microstructuring. In these works, the authors use:

• ultrashort pulse laser for microstructuring;

• phase-modulating PMS with pixels controlled by analog signals;

• a scheme with a projection of intermediate distributions or distributions of the field in the far zone on a reduced scale;

• light splitting phase gratings; And

• reveal how these techniques can be applied with a variety of materials and radiation sources to modify and structure surfaces.

[12] In all disclosed examples, phase gratings are used that split beams with coefficients less than 1:200. This may be due to the fact that, in the case of ultrashort pulsed radiation, the power distribution in partial beams in the real output distribution obtained by means of SLM based on the LCoS technology (Liquid Crystais on Silicon) is different from the theoretical distribution. This leads to a decrease in depth removal accuracy between areas subjected to parallel machining. The origins of this phenomenon have not yet been studied. It is assumed that overlap of phase information or crosstalk between the pixels of the SLM display is possible, as well as the special nature of the coherence of the applied laser radiation. Since these errors are still not fully understood, they cannot be compensated during the calculation of the phase values. If higher splitting factors and greater reliability in terms of material removal rates between beams are required, it is necessary to use a control loop on the measured beam profile as an input value.

Laser micromachining

[13] Laser micromachining allows for fast and flexible machining of photomasks, photo originals and modification of specific surfaces, as well as focused machining of certain solids with pico- and femtosecond laser radiation, i.e. the so-called "ultra-short-pulsed" radiation. An additional advantage of using ultrashort pulses is the wide range of materials suitable for machining. Thus, it is possible to create micron and submicron structures, in particular, in glasses, metals, metalloids, hard coatings and plastics.

[14] To create the smallest possible non-self-organizing structures using laser radiation, a single, sharply focused beam with a relatively large divergence is usually used. The resulting relatively high intensity maxima in the focal plane make it possible to create such structures with pulse energies in the nanoJoule range down to the lower microJoule range. To apply this technology to commercial machining speeds, the approach commonly used is to increase the pulse repetition rate and feed rate in beam delivery systems. Alternatively, adaptive beam shaping using high energy pulses can be used; PMS has proven to be effective for this purpose. Phase gratings applied to the display split the beam into hundreds or thousands of partial beams, thereby enabling parallel machining ([SIL13]). At the same time, a number of factors were identified that affect the quality of the created hologram and are not limited only by the quality of the phase calculation algorithm. Such factors are, for example, scattering and deflection of the optical projection in the case of LCoS displays due to the large bandwidth when using femtosecond lasers ([KUA09]; [JES1Q]; [HAS07]; [RON12]). This also limits the practically achievable machining speeds and, depending on the design, may also cause the full energy of the laser pulses to not be used and/or the achievable precision of parallel machining to be lower than that of single focus sequential machining.

Other Unsolved Problems Related to Ultrashort Pulsed Microstructuring

[15] One possible way to increase area ratio with high energy pulses is to use photomasks and a uniform flat top beam profile and to scale down the resulting distribution. Often, however, beam profiles cannot be made uniform, or can only be made uniform over a long period of time. In this case, an optical homogenizer would be required, providing for a stable and defined beam profile. However, in practice, the beam profiles of lasers with ultrashort high-energy pulses are unstable in time and very often deviate too much from the ideal Gaussian profile. In addition, the production of the photomask and the change of the photomask during structuring requires additional time.

[16] SLMs simply provide the ability to speed up photomask change. Phase-modulating SLMs also provide the ability to influence the laser beam profile. This allows you to program beam profiles and switch from one to another in a fraction of a second. However, the output distributions generated often differ from those theoretically predicted. The use of a control loop that measures the generated output beam profile makes it possible to solve the problem of phase error and create beam profiles that can be used for precise parallel microstructuring.

[17] Most of the currently known schemes of this type significantly limit the functionality of the laser system and often perform only one specific type of machining. Also, there are still no mass-produced devices capable of overcoming the error in the output distribution arising from the erroneous phase representation and poor quality of the primary laser beams. In most cases, it is also necessary to specify the current input beam profile as a boundary condition for the calculation methods used in such schemes, although it has been found that this is not necessary. In the optimized circuit, if an error occurs in the output distribution due to an erroneous input distribution, it would be automatically eliminated by the closed loop algorithm. This fact can be taken into account to create a monolithic electronic circuit of the "black box" type with the possibility of implementing various functions for beam splitting / beam formation for a primary beam of any type and regardless of the laser source.

The essence of the invention

[18] According to a first aspect of the invention, there is provided a method for adaptively splitting an at least partially coherent primary light beam by means of a spatial light modulator (SLM). The method includes the steps of creating a partially coherent primary light beam from a collimated laser beam from a source included in the list, including: nanosecond laser, picosecond laser, femtosecond laser, creating the desired field distribution in the far zone, independent of the profile of the coherent primary light beam , by modulating the phase of the primary light beam using a spatial light modulator (SLM), while the primary coherent light beam is directed to reflect on the display element of the spatial light modulator, thereby preventing the formation of the primary coherent light beam by any moving element, output from the primary of the light beam, after passing through the spatial light modulator, the control beam and the main beam, direct the far-field distribution generated by the SLM in the control beam to the sensor surface of the camera, and measure the control beam by the camera. In the first embodiment, the method includes the steps of passing the primary beam through the first focusing element configured to generate the far field distribution in the main beam onto the focal plane of the first focusing element in the form of a real output distribution, and projecting the far field distribution in the control beam to the sensor surface through the first focusing element. In the second variant, the method includes the steps of passing the control beam through the second focusing element configured to project the field distribution in the far zone only onto the sensor surface. In both the first and second embodiments, the method further includes the steps of ensuring that the dynamic range of the imaging camera is matched by means of a variable intensity controller to control the intensity of the input pilot beam depending on the desired field distribution in the far field, regardless of the average power of the main beam, and configuring a closed loop for allowing phase calculation for the display element of the spatial light modulator, in which the output signal from the camera is entered into a closed loop for a plurality of iterations of the phase calculation algorithm performed by the controller. In this case, in the first variant, the first focusing element is used without using the second focusing element, and in the second variant, the second focusing element is used without using the first focusing element.

[19] In a preferred embodiment, the method further includes the steps of structuring the solid surface by the main beam and controlling the structuring by adjusting the spatial light modulator to obtain a specific profile for the primary light beam.

[20] In another preferred embodiment using the first embodiment, the method further includes adjusting the focal plane of the first focusing element for the step of structuring the hard surface so that the focal plane corresponds to the hard surface.

[21] In another preferred embodiment using the first embodiment, the method further includes adjusting the focal plane of the first focusing element to match the intermediate plane, and displaying the intermediate plane on a reduced scale onto a solid surface by means of a projecting optical circuit.

[22] In another preferred embodiment, using the second option, in the patterning step, the far field distribution is used to obtain patterns on the solid surface by projecting the far field distribution onto the solid surface by means of a focusing optical circuit.

[23] In another preferred embodiment, a beam splitting element is used at the stage at which the removal is carried out. The method additionally includes the steps of: combining the beam splitting element, the first and second focusing elements, the spatial light modulator, the variable intensity controller and the shooting camera into a single compact body, the single compact body being made as an independent component with the possibility of being placed in the primary coherent light beam, switching between the first option and the second option by means of the control device, and adjusting the variable intensity controller by means of the control device.

[24] In another preferred embodiment using the second embodiment, the method further includes the steps of: splitting the primary light beam into a plurality of partial main beams by a spatial light modulator, individually adjusting several of the plurality of partial main beams, separation angles between each of the plurality partial main beams after the plurality of partial main beams leave the spatial light modulator display element, and intensity distribution between the partial main beams of the plurality of partial main beams by phase control. The distribution of intensities between the partial main beams of the plurality of partial main beams is controlled by a controller also configured to control individual generation for each of the plurality of partial main beams, the spatial light modulator, and the primary light beam. The method also includes the step of structuring the solid surface with a plurality of partial main beams.

[25] In another preferred embodiment, the hard surface includes any of the list, which includes metal, diamond, sapphire, glass, plastic, composite materials, leather.

[26] In another preferred embodiment, the hard surface is part of the working tool.

[27] In another preferred embodiment, the working tool is any one of an embossing roll, a stamping device, a metal tool, a watch component, a piece of jewelry, a packaging component.

[28] According to a second aspect of the invention, there is provided an apparatus capable of adaptively splitting a target at least partially coherent primary light beam by a spatial light modulator (SLM), wherein the target partially coherent primary light beam is a beam from a collimated laser beam from a source, included in the list, including: nanosecond laser, picosecond laser, femtosecond laser. The device comprises a spatial light modulator configured to create a desired far field distribution independent of the profile of the coherent primary light beam by phase modulating the target primary light beam, wherein the spatial light modulator is also configured to receive the primary light beam from the display element a spatial light modulator and, thereby, preventing the formation of a primary light beam by any moving element; a beam splitter located in the target primary light beam after it has passed through the spatial light modulator and configured to extract the target pilot beam and the target main beam from the primary light beam; and a filming camera located in the target control beam and additionally containing a sensor surface configured to measure the distribution of the field in the far zone created by the spatial light modulator in the control beam, while in the first configuration variant the device contains the first focusing element configured to project the distribution field in the far zone, created by the spatial light modulator in the control beam, onto the sensor surface, and also configured to pass the primary beam and generate the far field distribution in the main beam to the focal plane of the first focusing element in the form of a real output distribution. In the second configuration variant, the device comprises a second focusing element located in the target control beam and configured to project the distribution of the field in the far zone, created by the spatial light modulator, only onto the sensor surface. In both the first and second configurations, the device further comprises a variable intensity controller located in the target pilot beam in front of the imaging camera and configured to match the dynamic range of the imaging camera by controlling the intensity of the input target pilot beam depending on the desired far field distribution. , regardless of the average power of the main beam; a closed loop circuit configured to phase calculation for the display element of the spatial light modulator, comprising a controller connected to the shooting camera with the ability to receive an output signal and configured to apply the output signal for multiple iterations of the phase calculation algorithm performed in the controller. The device further comprises switching means configured to switch between the first configuration option and the second configuration option, wherein in the first configuration option the first focusing element is used without using the second focusing element, and in the second configuration option the second focusing element is used without using the first focusing element.

[29] According to a third aspect of the invention, there is provided an apparatus capable of machining a target hard surface, comprising an apparatus capable of adaptively splitting a target at least partially coherent primary light beam by a spatial light modulator (SLM). The device configured to machine the target hard surface is also configured to locate the target hard surface in the main beam, wherein the target hard surface is machined by at least adjusting the spatial light modulator to create a specific profile for the primary light beam.

[30] In another preferred embodiment, in which the adaptive splitting device is configured in the first configuration, the focal plane of the first focusing element (L1) is configured to correspond to a target hard surface.

[31] In another preferred embodiment, in which the device capable of adaptive splitting is configured in the first configuration, the device further comprises a display optical circuit, wherein the first focusing element is located so that the focal plane corresponds to the intermediate plane, while displaying the optical scheme is configured to display the intermediate plane on a reduced scale onto a solid surface.

[32] In another preferred embodiment, in which the device capable of adaptive splitting is configured in the second configuration, the device further comprises a focusing optical circuit, wherein the focusing optical circuit is configured to project a desired far-field distribution in the main beam far field onto hard surface for machining.

[33] In another preferred embodiment, the device further comprises a single compact body configured to combine the beam splitter element, the first and second focusing elements, the spatial light modulator, the variable intensity controller, and the imaging camera, the single compact body being configured as an independent component with the possibility of being placed in the primary light beam; wherein the controller is configured to control the switching means for switching between the first configuration option and the second configuration option and adjusting the variable intensity controller.

[34] In another preferred embodiment, the spatial light modulator is configured to split the primary light beam into a plurality of partial main beams and individually adjust several of the plurality of partial main beams, separation angles between each of the plurality of partial main beams after the plurality of partial main beams leave the display element. a spatial light modulator and intensity distribution between the partial main beams of the plurality of partial main beams by phase control, wherein the controller is also configured to control the distribution between the partial main beams of the plurality of partial main beams by controlling the spatial physical properties of each of the plurality of partial main beams, wherein the spatial physical properties are at least one of the following: phase and amplitude, spatial light modulator, and primary light beam. The device is also configured to locate the target hard surface in a plurality of main beams.

[35] In another preferred embodiment, the target solid surface is the surface of the target embossing roll, wherein the controller is also configured to position the surface of the target embossing roll in the main bundle.

[36] In another preferred embodiment, the target hard surface includes any of a list of metal, diamond, sapphire, glass, plastic, composite material, leather.

[37] In another preferred embodiment, the target hard surface is part of the target working tool. [38] In another preferred embodiment, the target working tool is any one of an embossing roll, a stamping device, a metal tool, a watch component, a jewelry piece, a packaging component.

Brief description of the drawings

[39] A clearer understanding of the invention can be obtained from the section "Preferred embodiments of the invention" and examples in the figures, of which:

[40] FIG. 1 shows the configuration of an SLM module according to one embodiment of the invention;

[41] FIG. 2 shows another configuration of the SLM module according to one embodiment of the invention;

[42] FIG. 3 depicts an alternative SLM module design using a mirror according to one embodiment of the invention;

[43] FIG. 4 shows a further alternative design of the SLM module, in which the focusing element is located in front of the SLM display, according to one embodiment of the invention;

[44] FIG. 5 shows a further alternative design of the SLM module, in which the focusing element is located in front of the SLM display, and includes only one mirror, according to one embodiment of the invention;

[45] FIG. 6 depicts a further alternative design of the SLM module, in which the focusing element is located behind a translucent mirror, according to one embodiment of the invention; [46] FIG. 7 depicts a further alternative design of an SLM module in which the focusing element is located behind a translucent mirror and includes only one mirror, according to one embodiment of the invention;

[47] FIG. 8 depicts a PMS module as a component of a microstructuring device according to one embodiment of the invention;

[48] FIG. 9 shows another PMS module as a component of a microstructuring device according to one embodiment of the invention;

[49] FIG. 10 shows an example of an application according to the invention in which parallel groove structuring is carried out with a relatively small pulse spacing;

[50] FIG. 11 shows another PMS module in the form of a controlled beam splitter according to one embodiment of the invention;

[51] FIG. 12 shows a further application example according to the invention, in which parallel groove structuring is carried out with a relatively large pulse spacing;

[52] FIG. 13 shows additional examples of applications according to the invention in which profiles are patterned with a 2-dimensional output distribution;

[53] FIG. 14a and 14b show additional application examples according to the invention for surface profiles perpendicular to the direction of propagation when patterning with an oblique 2D output distribution;

[54] FIG. 15a and 15b show additional application examples according to the invention for surface profiles in structuring with relatively small pulse spacing;

[55] FIG. 16a and 16b show further examples of applications according to the invention for surface profiles in structuring with comparatively large pulse spacings; And

[56] FIG. 17 shows an example of a device capable of machining the surface of an embossing roll.

Implementation of the invention

Purpose of the invention

[57] The purpose of the invention is to simplify for the user the process of beam formation and, in particular, the splitting of the laser beam. An additional objective of the invention, hereinafter referred to as the "PMS module", is to create a device and method that can be included in any optical path, with a relatively high degree of compactness and an individual set of functionality, regardless of the place of application. Another object of the invention is to enable the splitting of any type of collimated primary beam (laser source) with relatively high accuracy, regardless of beam profile, phase position, bandwidth/pulse width and laser power.

[58] One of the advantages provided by the invention is that any limitation for the SLM module can be predicted by understanding the properties of its main element - the SLM display as such. Another advantage is the possibility of beam splitting with very low losses. Thus, the input radiation will simply need to be modulated in phase, while this function can also be implemented using simultaneous amplitude modulation or only with it. Another advantage is that the invention provides the possibility of switching between the actual output distribution in the focal plane of the lens, i.e. Fourier plane, and the distribution of the field in the far zone, i.e. diffraction pattern at an infinite distance. Another advantage is the possibility of achieving a relatively high degree of accuracy in the generated output distribution, as well as in the distribution of power between different partial beams, by using a closed-loop solution for calculating phase values in the invention, independent of the input profile or the profile of the primary beam of the laser source. respectively.

[59] The proposed PMS module allows more efficient use of laser power due to the possibility of parallel mechanical micromachining and machining of hard surfaces through multiple beams. This can be done at a workstation via shared output optics, or on multiple systems simultaneously, with each of the multiple systems using a split primary beam common to all machining systems. Parallel machining makes it possible to reduce the process time in the case of machining large surfaces and volumes linearly with the specified number of partial beams. The use of a common output optics for all partial beams makes it possible to speed up the creation of grooves, lattice structures, and other frequently repeated regular structures. The PMS module according to the invention enables simultaneous and precise machining of a large number of partial beams, for example 1000 or more beams.

[60] In view of the above goals and properties, the proposed PMS module can significantly improve the performance of the laser micromachining / structuring device while maintaining the compact size of the device and high stability of the operation mode. This will reduce the cost and production time in industrial applications.

Structure and operation of the iterative Fourier transform algorithm (AFFT) - Closed loop modulus (CL) Mandatory requirements for the input beam

[61] The primary laser beam used in all aspects of the present invention must meet a number of criteria in order to use the functionality of the SLM module. The first criterion is that the primary beam at the input of the PMS module must be collimated or parallelized. One skilled in the art will recognize that the beam coherence length for wave optics and optical gratings should be approximately equal to the grating period. Since ultrashort pulsed radiation is used in the present invention, the time-dependent coherence length can also be very short, eg only a few micrometers.

[82] One of ordinary skill in the art also recognizes that if the LCP display of an LCP module contains a liquid crystal on silicon (LCoS) element, the input radiation must inherently conform to certain polarization states with respect to the orientation of the LCP display. It can be adjusted by installing commercially available structural elements in front of the PMS module. Therefore, this issue will not be considered further in this paper. It is also known that the functionality of LCoS technology is highly wavelength dependent.

[63] It is also well known that the user of the SLM module can select and adjust the beam diameter, average optical power or pulse energy, provided that the user does not exceed the limit of physical destruction of any component in the SLM module.

Structure of the PMS module

[64] From the following description, it will be understood that using the proposed method and apparatus, the user can split the primary input beam that meets the above criteria into an arbitrary number of output beams and apply them at his discretion. The user or control process can control the spatial distribution of the output beams and the distribution of their intensities as a function of time. The invention also allows the use of both a real intermediate distribution and a simple angular distribution, depending on which machining task is to be performed. The invention makes it possible to do this in the absence of precise information about the profile of the primary input beam or its coherence length. The invention does not provide for any other mandatory requirements for the primary input beam, in addition to those indicated above. Any deviations in the output main beam due to lack of information can be compensated for by the closed loop algorithm used to optimize the output distribution.

[65] The invention provides the possibility of creating a "black box" type optical system with the possibility of being included in optical paths of any type for mechanical micromachining.

[66] FIG. 1 depicts a configuration of an SLM module according to one exemplary embodiment of the invention in order to implement the features of the invention disclosed above. Mirror M1 directs radiation from the primary beam from a laser source, not shown in FIG. 1, but symbolically indicated by the position number 100 and the corresponding arrow in the drawing, at a relatively sharp angle to the reflective head 101 of the ICP. The PMS head 101 is considered to be the central element of the PMS module. The SLM head 101 includes an SLM display not explicitly shown in FIG. 1 configured to apply beamforming phase values to the input primary laser beam. The SLM display may, for example, be implemented on the basis of LCoS technology, which is also not explicitly indicated in FIG. 1. As is known to the person skilled in the art, LCoS type displays produce effects that affect the polarization of the radiation and thus the diffraction efficiency. To compensate for this effect, the PMS module contains an additional polarization beam splitter 102, placed behind the PMS display, which filters out incorrectly polarized and/or non-diffracted radiation. The PMS module also contains a translucent output mirror M2. The polarizing beam splitter 102 is installed in the optical path in front of the output mirror M2, due to which the distribution after reflection on the PMS display is guaranteed to appear in the same way on the CCD camera 104 located in the optical path of the control beam, separated from the primary beam by a semitransparent mirror M2, and in the plane 103 Fourier where the real output distribution occurs, or at infinity, as the case may be. The translucent mirror M2 can be made, for example, in the form of a mirror with a dielectric reflective coating and a plane-parallel substrate that is transparent to light with a wavelength of the primary beam. The surface quality of the M2 mirror preferably complies with the industry standard for transparent optics and glass surfaces. Thus, the control beam extracted/separated on mirror M2 can be used for beam analysis without excessive power loss, despite the relatively high beam power consumption under mechanical micromachining conditions. The variable intensity controller 105 in the optical path in front of the CCD camera 104 is configured to match the intensities to the dynamic range of the CCD camera 104 to enable its application in an optimal manner and regardless of the average primary beam power, output distribution and/or beam splitting factors. The variable intensity controller 105 may, for example, be in the form of an HC (Neutral Density (ND)) filter.

[67] In this section, "Carrying out the invention" we are talking about the head 101 SLM, used in the mode in which it reflects radiation from the primary beam, while in an additional preferred embodiment, it is possible to use the head 101 operating as a transmitter for the primary beam.

[68] The image captured by the CCD camera 104 should in any case be the result of the Fourier transform of the input distribution. Therefore, the touch surface (not shown in Fig. 1) of the CCD camera 104 must be located in the focal plane of the focusing optical element, for example, the first focusing element L1 and the second focusing element L2. In the example in FIG. 1, the first focusing element L1 and the second focusing element L2 are never placed together, i. simultaneously, into the optical path between the PMS head 101 and the CCD camera 104. The CCD camera 104 is preferably centered on the optical axis of the control beam output by the translucent mirror M2.

[69] The CCD camera 104 makes it possible to obtain a measurement of the output distribution, which in turn can serve as data input to a closed-loop control based on an iterative Fourier transform algorithm (IATF) to optimize the phase distribution generated by the ICP head 101. As mentioned above, this requires measuring the output distribution using the CCD camera 104 and entering it into the algorithm executing in the central processing unit 106 of the controller as part of the ACE boundary conditions. The ACE algorithm will not be discussed in detail in this document, since its description can be found in the literature of the prior art. The calculated phase values are then applied to the ICP display.

PMS module configuration

[70] The SLM module can be implemented in either of two hardware configurations to enable switching between angular distribution and actual intermediate distribution. Switching between these configurations, as well as changing the filter settings for the variable intensity controller, can be done manually or using automated switching tools.

[71] In the first hardware configuration, referred to herein as "configuration 1" and disclosed in FIG. 1, the first focusing element L1 is placed in the optical path. L1 focuses the laser light on the sensor surface of the CCD camera 104 placed at the focal length f(L1) L1 and behind the translucent mirror M2. In addition, the CCD camera 104 is placed in the plane of the main output beam perpendicular to the propagation direction of the main output beam, i. e. in the photomask plane. In the example in FIG. 1, the first focusing element L1 is located in front of the polarizing beam splitter 102. In an alternative embodiment not illustrated in FIG. 1, the first focusing element L1 may be located behind the polarizing beam splitter 102. In the configuration in Fig. 1, the second focusing element L2 with focal length f(L2) is not located in any optical path. The distribution recorded by the CCD camera 104 is identical and mirrored with respect to the photomask plane. Configuration 1 makes it possible to focus the main beam reflected from mirror M2 in a real intermediate distribution.

[72] FIG. 2 shows configuration 2, largely identical to configuration 1 in FIG. 1, except for the fact that the second focusing element L2 is located in the optical path of the control beam, which was extracted through the semitransparent mirror M2. The sensor surface (also not shown in FIG. 2) of the CCD camera 104 is in this case placed in the focal plane of the second focusing element L2, i. at a distance of focal length f(L2) of the focusing element L2. Thus, in configuration 2, L1 is not located in any optical path. Configuration 2 does not focus the main output beam reflected from mirror M2 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 many partial main beams.

Alternative designs

[73] The invention can be implemented in a variety of alternative designs with the same functionality. Each of these various alternative designs can be considered to have a number of disadvantages and advantages over configurations 1 and 2.

[74] FIG. 3 shows an alternative design containing only one dielectric mirror M - mirror M1 in FIG. 1 and 2 do not apply here. The dielectric mirror M must meet all the above requirements. The positions for the first focusing element L1 and the second focusing element L2 may be identical to those disclosed in FIG. 1 and 2 - directly in front of the dielectric mirror M or behind it. One advantage of this design over the design of FIG. 1 lies in its inherent greater compactness. In this case, the angle between the input beam and the output beam is fixed. The structure in Fig. 3 is in a mode similar to configuration 2 - for ease of understanding, let's say that it is made in configuration 2. To switch to configuration 1, the first focusing element L1 must be located in the optical path, and the second focusing element L2 must be removed from the optical path. The arrows next to the elements L1 and L2 symbolize these actions.

[75] FIG. 4 shows a further alternative design in configuration 1. In this alternative design, the first focusing element L1 is located at some distance in front of the SLM display, while, as in FIG. 1, two mirrors M1 and M2 are used. Both focusing elements L1 and L2 are movable, which is symbolized by the arrows next to the elements. This alternative design does not offer any obvious advantages. One potential difference from the design in FIG. 1 is that the focal length for the first focusing element L1, represented as f(L1)=a+b in this figure, may be greater than, for example, in FIG. 1, which in turn reduces the resolution of the output distribution.

[76] FIG. 5 shows a construction similar to that in FIG. 4, but in configuration 2, again using only one mirror M. The properties indicated for FIG. 3, also take place in this case: the device can be made more compact, but with limited convergence and splitting angles of the laser beam at the input and output of the PMS module.

[77] FIG. 6 shows the construction in configuration 2, in which a third focusing element L3 (eg a lens) with a focal length f(L3) is located behind the translucent mirror M2. For clarity, L1 is not shown in FIG. 6, since it is removed from the optical path in this scheme. The second focusing element L2 can be introduced into the optical path, which is symbolized by the arrows next to the second focusing element L2. The advantage is that the second focusing element L2 can be fixed in the optical path, i.e. it will no longer need to be moved when switching between configurations by moving L3.

[78] FIG. 7 shows a construction similar to that in FIG. 6, but with a single mirror M to make the device more compact.

Loss in the optical path

[79] One of the advantages of the proposed SLM module is the ability to form a beam essentially without loss. Therefore, there is no need to use absorbing photomasks or scattering photomasks to obtain the desired output distribution. Beam shaping is carried out solely by the phase distribution applied to the ICP head. In this case, it will be clear to a person skilled in the art that, in practice, small losses of the laser beam in optical paths are inevitable.

[80] When using ideal optical elements, only losses from scattering on the diffraction grating of the SLM will occur, and only for high-order diffraction, since the desired target distribution occurs exclusively in the first order of diffraction.

Applications and possible applications

Parallel microstructuring / parallel structuring

[81] The proposed method and device are designed to be used as part of any optical path, provided there is sufficient physical space for this and compliance with the above conditions for the laser beam. Fig. 8 depicts an example of a projection exposure microstructuring system in which the plane of the photomask in the optical path is replaced by the actual output distribution 103 of the SLM module 800 configured in configuration 1. The primary laser beam 801 from the laser source 802 is input to the SLM module 800. The actual output distribution 103 is projected onto the workpiece 803 through a microscope 804 of a micromachining head 805, also referred to as "parallel microstructuring tool". The workpiece 803 is mounted on a coordinate table 806, which is configured to move the workpiece 803 at least in the X-Y plane perpendicular to the projected light beam. The second filming camera 807 is configured to control the main beam projected onto the workpiece 803, as well as to function as part of an autofocus device. A person skilled in the art is familiar with the operation of optical systems and their parameters for projection photolithography. The scope of knowledge of a person skilled in the art essentially includes the parameters of the applicable phase distribution without any restrictions for the module 800 SLM. The controller CPU 106 is also configured to control the location of the focusing elements L1 and L'', as well as the variable intensity controller 105.

[82] FIG. 9 depicts an example of incorporating a PMS module 800 into a focused machining system. In this particular case, the PMS module 800 is in configuration 2. This increases the number of partial main beams that can be used for laser machining. Ideally, for most optical paths and the optics used in such a system, the SLM module 800 should preferably be located as close as possible to the final optics; in this example, this will be the micromachining head 805 to avoid any limitations due to its aperture.

[83] The increased number of focal points provides the beneficial effect of increasing the speeds of the laser machining process based on focused beams in proportion to the number of partial main output beams, as well as the possibility of optimizing the use of laser power. Switching between partial beam distribution and focal distribution can occur at a rate corresponding to the refresh rate of the image on the display head 101 SLM, without any moving part. One skilled in the art will recognize that phase modulation allows for correction of Zernike modes, which in turn improves focus quality. If the erroneous phase position of the primary beam is also known, it is possible to improve the quality of all partial main beams by means of the PMS module 800. The PMS module 800 does not affect display scaling factors and beam diameters.

Structuring Examples for Parallel Machining

[84] Parallel microstructuring by means of a plurality of partial main beams with individual control of pulse energy or beam power provides structuring capabilities similar to those using single beams. Fig. 10 schematically depicts the beam spacing dx for a pulsed primary beam split into n × m partial output beams. Symbols p1, p2, p3, etc. denote the sequence of pulses in time. The workpiece is moved along the x-axis of a rectangular distribution, with a spacing dx occurring between two laser pulses. In this way, a set of n lines can be created, with each line being irradiated several times, usually with little overlap. This results in a profile of lines of constant depth along the length of the line in the v direction, with the set of lines having a distribution f(x) of maximum depths as shown in FIG. 15b.

[85] Operating with such a small pulse spacing also allows for so-called "surface pickup" as shown in FIG. 15a. In this case, the workpiece is moved relative to the laser according to the feed direction v1 so as to cover the surface defined by adjacent partial beams. This allows you to create 2.5-dimensional surface reliefs.

[86] Another potential approach to parallel microstructuring is to space the partial beams by dx, as shown in FIG. 12. The interval traversed in the time between individual pulses will be somewhat greater than dx, and therefore the actual interval between individual pulses will be dn. In the particular example in Fig. 12, the number of pulses between two partial beams with a spacing dx will be m=5. The application of this machining strategy makes it possible to reduce the actual interval between individual pulses. The structuring time for simple lattices can be significantly reduced by applying optimized relationships between dx, dn and m.

[87] Another possibility is to tilt the periodic distribution of the output beam with respect to the feed direction by an angle "alpha", as illustrated in FIG. 13. Thus, each partial beam can create a line with a constant removal depth or radiation dose, while, depending on the angle "alpha", individual radiation marks can also overlap each other perpendicular to the feed direction v2. The visible interval dy' between pulses is the greater, the greater the tilt angle "alpha". By specifying the spatial distribution of partial beams in the x and y directions based on dx and dy respectively, one can generate an apparent intensity distribution in one dimension. In this way it is possible to create any type of section profile f(x) in a single pass - see also FIG. 14a and 14b. If all the lines in the output distribution are identical to each other, l identical profiles will be created at the same time - see FIG. 14a.

[88] When using a pulsed beam in operation, structuring along a partial beam allows you to put the removal depth or irradiation intensity in a periodic dependence f(x). To do this, the feed direction, the number of partial main beams along the line and their spacing must have a constant ratio. Fig. 16a shows the profile A along the left line in the v3 direction, as illustrated by the cross-sectional view in FIG. 16b. The momentum energy of partial beams along this line constantly decreases.

Structuring the surface of the embossing roller

[89] FIG. 17 illustrates an example of a device that can be used to structure an embossing pattern 1700 on a working tool, in particular on the surface of an embossing roll. The PMS module 800 introduces the primary light beam, i. e. collimated and at least partially coherent light from a laser source 802, and directs, at its output, the main beam onto the surface of the embossing roller. There are several options for adjusting the relative position of the PMS module 800 and the embossing roller. In the illustrated example, the ICP module 800 can be moved according to the indicated x direction, while the embossing roller can also be rotated by the motor 1701, as indicated by the circular arrows. The controller 106 is also configured to adjust the relative position of the ICP module 800 and the embossing roller, that is, to appropriately control the ICP module 800, the laser source 802, and the motor 1701 to emboss the embossing pattern 1700 onto the surface of the embossing roller.

beam splitting

[90] FIG. 11 illustrates the operating principle for splitting/beam splitting. Module 800 PMS in configuration 2 is located at the output of the source 802 of the laser beam. With regard to the primary laser beam 801, only the above restrictions are established. The diffraction of the primary laser beam 801 occurs on the phase grating calculated as described above into m partial main beams with their subsequent deflection by m differently oriented mirrors M1-Mm. Further, said mirrors reflect respective partial beams onto m different workstations, exposure devices and/or measuring stations or beam absorbers (block 1 - block m). The distribution of power between the partial beams, their number and exit angles can be controlled in time by switching the phase values on the head 101 PMS. This allows you to increase the efficiency of using laser power and perform various tasks with a single laser source. As mentioned above, the PMS module 800 also makes it possible to correct the aberrational Zernike modes and thereby improve the quality of each of the partial beams.

Literature

Claims (21)

1. A method for adaptively splitting an at least partially coherent primary light beam by means of a spatial light modulator (SLM), which includes the steps of: creating a partially coherent primary light beam from a collimated laser beam from a source included in the list, including: a nanosecond laser , picosecond laser, femtosecond laser, create the desired field distribution in the far zone, independent of the profile of the coherent primary light beam, by modulating the phase of the primary light beam using a spatial light modulator, while the primary coherent light beam is directed to be reflected on the display element of the spatial of the light modulator, thereby preventing the formation of a primary coherent light beam by any moving element, is removed from the primary light beam, after passing through the spatial light modulator, the control beam and at least one main beam direct the field distribution in the far field created by the spatial modulator of light in the reference beam onto the sensor surface of the camera and the control beam is measured by means of the camera, wherein in the first embodiment the method includes the step of passing the primary beam through the first focusing element (L1) configured to generate a far field distribution in the specified at least one main beam onto the focal plane of the first focusing element in the form of a real output distribution and projecting the far field distribution in the control beam onto the sensor surface by means of the first focusing element (L1), while in the second variant the method includes the step of carrying out control beam through the second focusing element (L2), made with the possibility of projecting the field distribution in the far zone only on the sensor surface, while in both the first and second versions they ensure compliance with the dynamic range of the shooting camera by means of a variable intensity controller to control the intensity of the input control beam depending on the desired field distribution in the far zone, regardless of the average power of said at least one main beam, a closed loop is configured to enable phase calculation for the imaging element of the spatial light modulator, in which the output signal from the camera is injected into a closed loop for a set iterations of the phase calculation algorithm performed by the controller, wherein in the first variant the first focusing element is used without using the second focusing element, and in the second variant the second focusing element is used without using the first focusing element. 2. The method according to claim 1, further comprising the steps of: structuring the solid surface by said at least one main beam and controlling the structuring by adjusting the spatial light modulator to obtain a specific profile for the primary light beam. 3. The method of claim 2 using the first embodiment, further comprising adjusting the focal plane of the first focusing element for the step of structuring the hard surface so that the focal plane corresponds to the hard surface. 4. The method according to claim 2, using the first option, further comprising the steps of: adjusting the focal plane of the first focusing element so that it corresponds to the intermediate plane, and displaying the intermediate plane on a reduced scale onto a solid surface by means of a projecting optical circuit. 5. The method according to claim 2, using the second option, in which, in the step of structuring, the far-field distribution is used to obtain patterns on the solid surface by projecting the far-field field distribution onto the solid surface by means of a focusing optical circuit. 6. The method according to any one of paragraphs. 1 - 5, in which at the stage at which the beam splitting element is used, the method further includes the steps of: combining the beam splitting element, the first and second focusing elements, the spatial light modulator, the variable intensity controller and the shooting camera into a single compact body, and a single compact body is made as an independent component with the possibility of being placed in the primary coherent light beam, switching between the first option and the second option is carried out by means of the control device and the variable intensity controller is adjusted by means of the control device. 7. The method according to any one of paragraphs. 1, 2, using the second option, further comprising the steps of: splitting the primary light beam into a plurality of partial main beams by a spatial light modulator, individually adjusting several of the plurality of partial main beams, separation angles between each of the plurality of partial main beams after leaving a plurality of partial main beams of the imaging element of the spatial light modulator and an intensity distribution between the partial main beams of the plurality of partial main beams by phase control, wherein the intensity distribution between the partial main beams of the plurality of partial main beams is controlled by a controller also configured to control individual generation for each of the plurality partial main beams, a spatial light modulator and a primary light beam, and structuring the solid surface through a plurality of partial main beams. 8. The method according to any one of paragraphs. 2 - 5, in which the hard surface includes any of the list, which includes metal, diamond, sapphire, glass, plastic, composite materials, leather. 9. The method according to any one of paragraphs. 2-5 and 8, in which the hard surface is part of the working tool. 10. The method of claim. 9, wherein the working tool is any of the list, which includes an embossing roller, a stamping device, a metal tool, a wrist watch component, a piece of jewelry, a packaging component. 11. An adaptive light beam splitter by a spatial light modulator configured to adaptively split a target at least partially coherent primary light beam by a spatial light modulator (SLM), wherein the target partially coherent primary light beam is a beam from a collimated laser beam from a source , included in the list, including: a nanosecond laser, a picosecond laser, a femtosecond laser, while the device contains: a spatial light modulator configured to create the desired field distribution in the far zone, independent of the profile of the coherent primary light beam, by modulating the phase of the target a primary light beam, wherein the spatial light modulator is also configured to receive the primary light beam from the display element of the spatial light modulator and thereby prevent any moving element from generating the primary light beam; a beam splitter located in the target primary light beam after it has passed through the spatial light modulator and configured to extract the target pilot beam and the target at least one main beam from the primary light beam; a shooting camera located in the target control beam and additionally containing a sensor surface configured to measure the distribution of the field in the far zone created by the spatial light modulator in the control beam, and in the first configuration variant, the device contains the first focusing element (L1) configured to project field distribution in the far zone, created by a spatial light modulator in the control beam, onto the sensor surface, and also configured to conduct the primary beam and generate the field distribution in the far zone in the specified at least one main beam onto the focal plane of the first focusing element in the form of a real output distribution; in this case, in the second configuration variant, the device contains a second focusing element (L2) located in the target control beam and configured to project the field distribution in the far zone, created by the spatial light modulator, only onto the sensor surface, while both in the first and in the second configuration options, the device further comprises a variable intensity controller located in the target pilot beam in front of the imaging camera and configured to match the dynamic range of the imaging camera by controlling the intensity of the input target pilot beam depending on the desired field distribution in the far field, regardless of the average power specified by the camera. at least one main beam; a closed loop circuit configured to phase calculation for the display element of the spatial light modulator, comprising a controller connected to the shooting camera with the ability to receive an output signal and configured to apply the output signal for a plurality of iterations of the phase calculation algorithm performed in the controller, while the device additionally contains switching means configured to switch between the first configuration option and the second configuration option, wherein the first configuration option provides for the use of the first focusing element without using the second focusing element, and the second configuration option provides for using the second focusing element without using the first focusing element. 12. A hard surface laser processing device with adaptive light beam splitting, configured to machine the target hard surface, comprising the device according to claim 11, wherein the device configured to machine the target hard surface is also configured to position the target hard surface in the specified at least one main beam, and the machining of the target hard surface occurs as a result of at least adjusting the spatial light modulator to create a specific profile for the primary light beam. 13. The apparatus of claim 12, wherein the apparatus of claim 11 is configured in a first configuration, wherein the focal plane of the first focusing element (L1) is configured to conform to a target hard surface. 14. The device according to claim 12, in which the device according to claim 11 is made in the first configuration option, additionally containing a display optical circuit, while the first focusing element is located so that its focal plane corresponds to the intermediate plane, while the display optical circuit is made with the ability to display the intermediate plane in a reduced scale on a solid surface. 15. The device according to claim 12, in which the device according to claim 11 is made in the second configuration option, additionally containing a focusing optical circuit, while the focusing optical circuit is configured to project the desired field distribution in the far field of the specified at least one main beam onto hard surface for machining. 16. The device according to any one of paragraphs. 11 - 15, additionally containing a single compact body, made with the possibility of combining the beam splitting element, the first and second focusing elements, the spatial light modulator, the variable intensity controller and the filming camera, and the single compact body is made as an independent component with the possibility of being placed in the primary light beam; wherein the controller is configured to control the switching means for switching between the first configuration option and the second configuration option and adjusting the variable intensity controller. 17. The apparatus of claim 12, wherein the spatial light modulator is configured to split the primary light beam into a plurality of partial main beams and individually adjust several of the plurality of partial main beams, separation angles between each of the plurality of partial main beams after leaving the plurality of partial main beams display element of the spatial light modulator and the distribution of intensities between the partial main beams of the plurality of partial main beams by phase control, the controller is also configured to control the distribution between the partial main beams of the plurality of partial main beams by controlling the spatial physical properties of each of the plurality of partial main beams, moreover, the spatial the physical properties are at least one of the following: phase and amplitude, spatial light modulator, and primary light beam, wherein the device is also configured to position the target solid surface in a plurality of main beams. 18. The device according to any one of paragraphs. 12-17, wherein the target hard surface is the surface of the target embossing roll, wherein the controller is also configured to position the surface of the target embossing roll in the main bundle. 19. The device according to any one of paragraphs. 12 - 15, in which the target hard surface includes any of the list, which includes metal, diamond, sapphire, glass, plastic, composite material, leather. 20. The device according to any one of paragraphs. 12-15 and 19 in which the target hard surface is part of the target working tool. 21. The device of claim. 20, wherein the target working tool is any of the list, which includes an embossing roller, a stamping device, a metal tool, a watch component, a piece of jewelry, a packaging component.

Images