Method for manufacturing a continuous diffraction optical element, device for implementing the method and continuous diffraction optical element
By using a heated laser beam to process the dielectric layer in a laser mirror, a continuous DOE with high diffraction efficiency is manufactured, solving the problems of manufacturing complexity and thermal damage limitations in existing DOE technologies, and realizing high-precision and high-efficiency laser beam forming.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- RHEINISCHE FRIEDRICH WILHELMS UNIVERSITAT BONN
- Filing Date
- 2021-02-18
- Publication Date
- 2026-07-21
AI Technical Summary
In the prior art, the manufacturing process of high-diffraction-efficiency diffractive optical elements (DOEs) is complex and limited by the number of steps in multi-stage DOEs, resulting in low diffraction efficiency. Furthermore, the use of quasi-continuous DOEs in high-power lasers is limited by the low thermal damage threshold.
By using a focused heated laser beam in a laser mirror to process the dielectric layer, multiple protrusions are generated to create a continuous DOE, avoiding the addition and removal of additional materials, achieving high diffraction efficiency, and making it suitable for high-power lasers.
It achieves a manufacturing precision of up to 2500 steps and a diffraction efficiency of up to 99%, and is suitable for laser beam forming with wavelengths of 100nm and above, and is applicable to high-power lasers.
Smart Images
Figure CN115968448B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing a continuous diffractive optical element for beam shaping a laser beam having a first wavelength.
[0002] Furthermore, the present invention relates to an apparatus for carrying out the above-described method and a continuous diffraction optical element. Background Technology
[0003] A diffractive optical element (DOE) allows for beam shaping of a laser beam, that is, targeted variation of the intensity distribution of the laser beam profile perpendicular to the propagation direction. To shape the beam, a DOE is introduced into the laser beam, where phase modulation of the beam occurs due to the different optical path lengths at the DOE, thus producing an interference pattern. The intensity of the laser beam is spatially modulated through constructive and destructive superposition. In this way, the typically Gaussian intensity distribution of the laser beam can be targeted and, for example, transformed into a toroidal intensity distribution.
[0004] Known DOEs in the prior art are glass or plastic substrates on which microstructures are applied by laser lithography and / or photolithography, as well as by various wet and dry chemical etching processes. For example, blazed gratings can be used as microstructures, i.e., gratings in which each grating line has a triangular sawtooth cross-section, resulting in maximizing the diffraction efficiency of a particular diffraction order.
[0005] However, fabricating DOEs with high diffraction efficiency is extremely complex. To achieve high diffraction efficiency, the microstructure must have a height profile that is as continuous as possible, which in turn requires very high-tech fabrication work. Due to the fabrication method using photolithography etching, the height profile is typically approximated by a stepped profile with a discrete number of steps. This height profile is better approximated by increasing the number of steps through repeated photolithography etching processes. Such DOEs with multiple steps are called multi-stage DOEs. However, due to this process, the number of steps is limited to approximately 16 because after about four repetitions of the etching process, fabrication-related inaccuracies increase and higher diffraction efficiency is not achieved. Therefore, the diffraction efficiency of multi-stage DOEs is physically limited to approximately 98%.
[0006] Furthermore, quasi-continuous DOEs are known in the prior art, fabricated via two-photon polymerization using maskless photolithography. For this purpose, the polymer applied to the substrate is typically directly structured by laser radiation. Quasi-continuous DOEs exhibit diffraction efficiencies equivalent to more than 50 steps. However, the use of such quasi-continuous DOEs is limited because the low thermal damage threshold of the polymers makes them unsuitable for high-power lasers.
[0007] The publication Smjuk, AY, Lawandy, NM: Direct Laser Writing of Glass Diffractive Optics, Opt. Lett., 1997, Vol. 22, No. 13, pp. 1030-1032, describes a method for fabricating diffractive optical elements from semiconductor-doped glass using a low-power laser and a thermal expansion process.
[0008] The publication Shore, BW et al., "Design of High-Efficiency Dielectric Reflective Gratings," J. Opt. Soc. Am. A, 1997, Vol. 14, No. 5, pp. 1124-1136, describes design examples for purely dielectric reflective gratings and comments on the relationship between transmission and reflection gratings. Furthermore, it describes examples of high-efficiency (95%) gratings fabricated using multilayers of hafnium and silicon dioxide.
[0009] Document US2009 / 0273772A1 describes a light reflection mask, which includes a reflective layer disposed on a substrate and reflecting light, an absorber layer disposed on the reflective layer and absorbing light, a device pattern formed in a first region of the absorber layer, and a reflectivity measurement pattern formed in a second region of the absorber layer. Summary of the Invention
[0010] Therefore, the object of the present invention is to provide a DOE, a method for manufacturing the DOE, and an apparatus for carrying out the manufacturing method, wherein the DOE has high diffraction efficiency and is suitable for beam shaping of high-power lasers.
[0011] This objective is achieved through the features of the independent patent claims. Preferred improvements are found in the dependent claims.
[0012] This invention relates to a method for manufacturing a diffractive optical element for beam shaping a laser beam having a first wavelength of at least 100 nm, the method comprising the following steps:
[0013] - Provide a laser mirror having a layered structure made of a substrate, a dielectric layer, and an optional absorption layer, wherein the dielectric layer abuts against the substrate or the absorption layer is located between the substrate and the dielectric layer.
[0014] - A plurality of protrusions in a dielectric layer are generated by processing a laser mirror with a series of focused heated laser beams having a second wavelength, the plurality of protrusions having a height perpendicular to the dielectric layer, and at least one protrusion having a height of at least half of the first wavelength.
[0015] The core of this invention lies in the fact that continuous DOEs are manufactured by creating protrusions in a laser mirror through target heating. This method allows for the manufacture of DOEs with very high diffraction efficiency, which translates into manufacturing precision for quasi-continuous DOEs, potentially corresponding to more than 2500 steps. The provided laser mirror and the DOE manufactured by this method comprise a substrate, an optional absorber layer, and a dielectric layer, all preferably parallel to each other, with the dielectric layer abutting against the substrate, or, in the presence of an absorber layer, disposed between the substrate and the dielectric layer. Specifically, the lower side of the dielectric layer or the lower side of the absorber layer is provided adjacent to the upper side of the substrate. More preferably, when an absorber layer is present, the upper side of the absorber layer is adjacent to the lower side of the dielectric layer. In other words, the upper side of the dielectric layer corresponds to the upper side of the DOE or the upper side of the laser mirror.
[0016] Compared to known prior art methods that fabricate DOEs by creating microstructures through the addition and / or removal of materials, this method provides microstructuring by generating multiple protrusions in the dielectric layer of the laser mirror. Therefore, after processing the laser mirror with a series of focused heated laser beams having a second wavelength, it is not necessary to apply or remove additional material layers to fabricate a DOE with very high diffraction efficiency. In other words, the DOE is fabricated by providing a laser mirror that itself comprises a substrate and a dielectric layer, and then directly processing the laser mirror with focused heated laser beams, thus without adding and / or removing material. Compared to prior art methods, the time-consuming photolithography and / or coating processes are avoided in the method according to the invention.
[0017] In this method, bumps are created in the dielectric layer, resulting in microstructuring of the dielectric layer surface. This specifically means that the surface of the dielectric layer after this method is not flat, but rather consists of local regions with different heights compared to before the method. The height of the bump refers to the extent to which the bump extends perpendicularly to the dielectric layer relative to the region surrounding the local region. The bumps are preferably rotationally symmetric, with the axis of rotation perpendicular to the absorption layer. For example, the bumps are circular when projected onto a plane parallel to the absorption layer. For rotationally symmetric bumps, the full width at half maximum (FWHM) is further preferably no greater than 6 μm.
[0018] The height of the protrusion affects the beam shaping of a laser beam having a first wavelength, because beam shaping with a DOE is only possible if at least one protrusion has a height of at least half the first wavelength. This method makes it possible to manufacture a DOE suitable for shaping laser beams with a first wavelength of at least 100 nm. In other words, this means that at least one protrusion has a height greater than 50 nm.
[0019] This method offers the following advantages: bumps can be generated in a targeted manner by processing with a heated laser beam, wherein, on the one hand, the position and height of the bump relative to a plane parallel to the dielectric layer are controllable. This method can be used to generate bumps with different heights, with a height resolution of at least 0.5 nm. Specifically, the height resolution is at least 0.1 nm. In other words, this method allows for the fabrication of very finely graded height profiles for structuring. Therefore, this method can fabricate continuous DOEs with very high diffraction efficiency, which translates into the fabrication precision of quasi-continuous DOEs, corresponding to more than 2500 steps.
[0020] Regarding the height of the bulge and the full width at half maximum (FWHM) in the case of a rotationally symmetric bulge, it is preferably specified that, to determine these parameters, a morphological record of the dielectric layer is created using a Mirau interferometer. The Mirau interferometer comprises an illumination source with a short coherence length, a green LED preferably having a center wavelength λ = 530 nm, a camera (DCC1545M, Thorlabs) for image acquisition, and a Mirau microscope objective (CF Plan 20xDI, Nikon). The front facet of the Mirau microscope objective preferably serves as a beam splitter, with half of the LED light reflected back to a reference mirror inside the Mirau microscope objective. This half of the LED light preferentially passes through the reference arm of the interferometer. The LED light transmitted through the front facet is preferably reflected back by the dielectric layer of the DOE and overlaps with the LED light of the reference arm. To ensure that the interference pattern is visible on the camera despite the low coherence length of the LED light, except for a few wave trains (z0≈z...),... Ref. In addition, the path lengths of the two interferometer arms are preferably chosen to be the same. The morphology of the dielectric layer of the DOE is preferably created by slowly moving the DOE about one micrometer using a piezoelectric crystal (timescale ~second) while recording the interferometric images using a camera. Then, preferably, for each pixel of the camera (x = 1 to 1000; y = 1 to 1000), a brightness sequence is created from the stored records (typically 50 interferometric images). The phase φ0(x,y) of each pixel can be determined by assigning an angular frequency ω to the function ~sin(ωt+φ0). This is preferably done for all pixels (x,y) of the camera so that a phase map can be created, where the adjusted phase can be input at any location in the camera image. Phase jumps between adjacent pixels may occur in the phase map because the adjusted phase is confined to the range of 0 to 2π. Phase discontinuities can be resolved by extending the range beyond 0 to 2π (phase unrolling). The phase φ0(x,y) in the phase map can then be converted to the height h(x,y) using the following formula:
[0021]
[0022] A topographic map of the DOE dielectric layer is created in this manner. Regions without protrusions in the topographic map are preferably used to determine the height of the protrusions so that a reference height is set to zero. The data points from the topographic map of the dielectric layer are then preferably used to adapt a function to the regions with protrusions, the function corresponding to the height profile of the protrusions. A two-dimensional Gaussian function is preferably suitable for rotationally symmetric protrusions. More preferably, the height of the protrusion and the full width at half maximum (FWHM) of the protrusion are determined by an adaptation function.
[0023] A preferred improvement is that the provided laser mirror is suitable for reflecting laser light of a first wavelength. The laser mirror provided in the first step of the method, and which practically represents the blank of the DOE, is preferably a highly reflective laser mirror for reflecting a laser beam having a first wavelength. Here, high reflectivity means that the laser mirror has a reflectivity greater than 99% for the first wavelength. In particular, a pre-coated dielectric laser mirror can be used. Further preferably, the laser mirror is suitable for reflecting laser light with a first wavelength greater than 100 nm. Regarding the use of the DOE for beam shaping in high-power lasers, it is further preferably provided that the laser mirror is suitable for reflecting laser light with a power greater than 100 W / cm. This also means that the laser mirror preferably has at least 0.5 J / cm when the pulse duration is a few picoseconds, i.e., 1-30 ps. 2 High damage threshold.
[0024] In this document, according to a preferred improvement of the invention, the provided laser mirror and diffractive optical element have T≤10 for the first wavelength. -2 The method specifies the generation of protrusions so that the dielectric layer maintains its high reflectivity. This also means that treating the laser mirror with a series of focused heated laser beams having a second wavelength will not damage the dielectric layer. Preferably, the transmittance is determined by measuring the laser power at the first wavelength before and after the diffractive optical element using a power-calibrated photodiode.
[0025] A preferred improvement of the invention is that the absorber layer is composed of silicon or gold, and / or the substrate is composed of glass, CaF2, MgF2, or sapphire, and / or the dielectric layer is composed of SiO2, Ta2O5, TiO2, HfO2, Al2O3, MgF2, LaF3, and / or ZrO2. The silicon in the absorber layer is particularly preferably amorphous silicon. It is also preferred that the substrate is composed of quartz glass to enable the forming of high-power laser beams. Further preferably, the dielectric layer comprises multiple layers of different materials, a first material having a high refractive index relative to the first wavelength, and a second material having a low refractive index relative to the first wavelength. Further preferably, the dielectric layer is composed of alternating layers of high-refractive-index and low-refractive-index materials. In particular, the dielectric layer is designed such that a laser beam having the first wavelength is reflected at the dielectric layer. In other words, this means that for both the provided laser mirror and the DOE manufactured by this method, the dielectric layer reflects more than 99% of the first wavelength.
[0026] Regarding the generation of protrusions, the method specifies that when a laser mirror is processed using a series of focused heated laser beams, the heat generated from the heated laser beams input to the volume of the dielectric layer or the absorption layer of the laser mirror must be at least 30 kJ / cm². 3 This makes it possible to generate bumps with a height greater than 50 nm in a particularly simple way.
[0027] Regarding the height of the protrusion, the method specifies that the height of the protrusion can be affected by the thermal input of the heating laser beam per volume entering the absorption layer and / or dielectric layer. A preferred improvement specifies that when the laser mirror is processed using a series of focused heating laser beams, the second wavelength, the power of the heating laser beam, the focusing of the heating laser beam, the heating duration, the absorption layer of the laser mirror, and the layer thickness of the dielectric layer and / or absorption layer of the laser mirror are selected such that at least one protrusion has a height of at least half of the first wavelength.
[0028] The thermal input of the heated laser beam can be controlled by different parameters. The wavelength of the heated laser beam (i.e., the second wavelength) is preferably matched to the absorption spectrum of the absorbing layer and / or the dielectric layer. This ensures that a portion of the heated laser beam is absorbed by the absorbing layer and / or the dielectric layer.
[0029] In this document, preferred modifications are specified where, when the laser mirror is treated with a series of focused heated laser beams, the second wavelength is between 200 and 700 nm and the absorbing layer of the laser mirror is made of silicon; or the second wavelength is between 200 and 2000 nm and the absorbing layer of the laser mirror is made of gold; and / or the second wavelength is between 100 and 2000 nm. These combinations of the wavelength of the heated laser beams and the absorbing layer allow for the reliable generation of protrusions greater than 50 nm. If the absorbing layer is omitted, a UV laser having a second wavelength in the range of 100 to 400 nm is preferably used to treat the laser mirror with a series of focused heated laser beams.
[0030] As already mentioned, the amount of heat per volume of the heated laser beam input into the absorption layer and / or dielectric layer can be affected by the power of the heated laser beam. In this respect, according to a preferred improvement, when the laser mirror is treated with a series of focused heated laser beams, the power of the heated laser beam is at least 10 mW. The power is particularly preferably between 10 and 1000 mW.
[0031] It is also preferably specified that the power of the heating laser beams be varied when the laser mirror is treated with a series of focused heating laser beams. This makes it easy to change the height of the protrusion. Specifically, by changing the power of the heating laser beams, it is particularly easy to produce protrusions with different heights and to produce a height resolution of at least 0.5 nm.
[0032] Regarding the formation of the protrusion, a preferred improvement is that when the laser mirror is treated with a series of focused heated laser beams, the heated laser beams penetrate the substrate of the laser mirror and strike the absorption layer and / or dielectric layer perpendicularly. In other words, this means that the back side of the laser mirror is irradiated by a series of focused heated laser beams. More preferably, the wavelength of the laser mirror substrate and the wavelength of the heated laser beams—i.e., the second wavelength—are matched so that the heated laser beams are substantially not absorbed by the substrate.
[0033] As already mentioned, the amount of heat input per volume of the heated laser beam into the absorption layer and / or dielectric layer can be controlled by different parameters. In this paper, when processing a laser mirror using a series of focused heated laser beams, the heated laser beams are focused onto the absorption layer and / or dielectric layer, with a full width at half maximum (FWHM) of at most 5 μm. Particularly preferred is that the FWHM of the heated laser beam is 1.8 μm or less. This allows for localized heat input within the absorption layer and / or dielectric layer, thus making the protrusions in the dielectric layer also localized. Specifically, this focusing can be used to create multiple protrusions, preferably spaced 3 μm or less apart. The distance between two protrusions preferably refers to the distance between the peaks of the two protrusions in a plane perpendicular to the absorption layer.
[0034] A further preferred improvement of the invention specifies that when the laser mirror is treated with a series of focused heating laser beams, the heating duration of the laser beams is between 1 μs and 1 ms. This has proven particularly suitable for producing bumps with a height greater than 50 nm. Shorter heating durations can lead to damage to the provided laser mirror. Longer heating durations can lead to damage to the dielectric layer, particularly resulting in the loss of the high reflectivity of the DOE.
[0035] In addition to the parameters already mentioned—namely, the second wavelength, the power of the heating laser beam, the focusing of the heating laser beam, the heating duration, and the optional absorption and dielectric layers of the laser mirror—the thickness of the absorption layer also affects the height of the bump. The thickness of the absorption layer refers to the extent to which the absorption layer extends perpendicular to its extension. A preferred improvement specifies that the thickness of the absorption layer is greater than 30 nm. Particularly preferably, the thickness of the absorption layer is greater than 40 nm. This makes it particularly easy to generate high heat input per unit volume in the absorption layer, thus allowing the bump height to exceed 50 nm.
[0036] A preferred improvement of the invention specifies that when a series of focused heating laser beams are used at a depth of at least 0.25 cm... 2 When processing a laser mirror on an area, the protrusions among a plurality of protrusions are formed in a grid-like arrangement relative to each other. The grid-like arrangement of the protrusions preferably refers to an arrangement parallel to the plane of the absorption layer, and the grid-like arrangement can be oblique, rectangular, centrally rectangular, hexagonal, or square. Translational symmetry deviations relative to the grid-like arrangement are also possible. More preferably, the plurality of protrusions exist within a distance of at least 0.25 cm. 2 On the surface area, the protrusions are preferably spaced 3 μm or less. The distance between two protrusions preferably refers to the interpeak distance between two protrusions in a plane perpendicular to the absorber layer.
[0037] In principle, it is possible that when a laser mirror is treated with a series of focused heated laser beams, the heated laser beams can be deflected two-dimensionally during the treatment and the laser mirror does not shift during this period. This reliably achieves a raised, grid-like arrangement. However, a preferred improvement to this method specifies that when the laser mirror is treated with a series of focused heated laser beams, the laser mirror is displaced along a direction perpendicular to the displacement of the heated laser beams during treatment, and the heated laser beams are deflected perpendicular to the displacement direction during treatment. This makes it possible to fabricate DOEs in a particularly fast and precise manner, with dielectric layers at least 0.25 cm... 2The surface has multiple protrusions arranged in a grid-like pattern relative to each other. Furthermore, this necessitates the necessary precision, such that the protrusions are preferably spaced 3 μm or less apart from each other. By displacing the laser mirror along a direction perpendicular to the displacement of the heating laser beam during processing, and by deflecting the heating laser beam perpendicular to the displacement direction during processing, a resolution of 0.25 cm can be achieved in less than 60 minutes. 2 Multiple protrusions are generated on the area.
[0038] Other advantages and technical features of the method for manufacturing a DOE will be apparent to those skilled in the art from the description of the DOE, the description of the apparatus for performing the method, and the description of exemplary embodiments.
[0039] Furthermore, the present invention relates to a diffractive optical element (DOE) for beam shaping a laser beam having a first wavelength of at least 100 nm. The diffractive optical element has a layered structure made of a substrate, optionally an absorption layer and a dielectric layer, wherein the dielectric layer is adjacent to the substrate or the absorption layer is located between the substrate and the dielectric layer. The dielectric layer has a plurality of protrusions having a height perpendicular to the dielectric layer, and at least one protrusion having a height greater than half of the first wavelength.
[0040] Therefore, the core of this invention lies in the fact that the different optical path lengths required for beam shaping of a laser beam are achieved on the DOE through protrusions in the dielectric layer. This allows for very high diffraction efficiency, which translates into manufacturing precision for a quasi-continuous DOE, corresponding to more than 2500 steps. Preferably, the height of at least one protrusion of the DOE is greater than 50 nm. The DOE is therefore preferably suitable for beam shaping of laser beams with a first wavelength greater than 100 nm. Furthermore, it is preferred that the protrusion is Gaussian relative to the plane perpendicular to the dielectric layer and has a full width at half maximum (FWHM) of at least 2 μm. More preferably, the FWHM is no greater than 6 μm.
[0041] Specifically, the DOE is a reflective DOE. This means that beam shaping of a laser beam with a first wavelength occurs through reflection of the laser beam on a diffractive optical element. Therefore, in contrast to a DOE in which the laser beam is formed by transmission through a DOE (transmission DOE), a DOE in which the laser beam is reflected is preferred. Compared to a transmission DOE, this has the advantage of only low absorption loss and the ability to achieve high efficiency.
[0042] Furthermore, the present invention relates to an apparatus for performing the above-described method, comprising a heating laser for generating a heated laser beam having a second wavelength, a laser mirror positioning device for providing a laser mirror, a focusing device for focusing the heated laser beam onto the laser mirror, a deflection device, and a controller. The laser mirror positioning device is designed to displace the laser mirror in a displacement direction, the deflection device is designed to deflect the heated laser beam perpendicular to the displacement direction, and the controller is designed to actuate the heating laser, the deflection device, and the laser mirror positioning device. Specifically, the deflection device is designed to deflect the heated laser beam in one direction. In other words, the deflection device is preferably a one-dimensional deflection device. The advantage of such deflection devices is that they can set very large deflection angles with high precision and speed. In order to generate a grid-like arrangement of protrusions by means of the apparatus, the laser mirror positioning device is designed to allow the laser mirror to be displaced in the displacement direction. The laser mirror positioning device is preferably a computer-controlled positioning stage with nanometer resolution. Attached Figure Description
[0043] For further advantages and technical features of the manufacturing method of the diffractive optical element, the diffractive optical element, and the apparatus for implementing the method, please refer to the accompanying drawings and further description.
[0044] The invention will now be explained by way of example using preferred embodiments with reference to the accompanying drawings.
[0045] The attached figure shows
[0046] Figure 1 This is a schematic diagram of a method for manufacturing a diffractive optical element according to a preferred embodiment of the present invention, and a cross-sectional representation of the diffractive optical element.
[0047] Figure 2 This is an illustrative apparatus for implementing a method for manufacturing a diffractive optical element according to a preferred embodiment of the present invention. Detailed Implementation
[0048] Figure 1A schematic diagram of a method for manufacturing a diffractive optical element 10 (DOE 10) according to a preferred embodiment of the present invention and a cross-sectional view of the DOE 10 are shown. The method provides two steps, in the first step of which a laser mirror 12 is provided as a blank for the DOE 10. The laser mirror 12 is adapted to reflect a laser beam having a first wavelength λ1. In this embodiment, the laser mirror 12 is for reflecting a laser beam with a wavelength λ1 of 532 nm (i.e., laser in the green wavelength range). Furthermore, the laser mirror 12 is suitable for high-power lasers and has a high damage threshold. In this example embodiment, the laser mirror 12 has a layered structure made of a substrate 14, an absorption layer 16, and a dielectric layer 18. In this embodiment, all three layers 14, 16, and 18 are parallel to each other, with the absorption layer 16 disposed between the substrate 14 and the dielectric layer 18. The dielectric layer 18 further comprises a plurality of material layers 20, 22 made of two different materials stacked alternately, the first material having a high refractive index relative to the first wavelength λ1 and the second material having a low refractive index relative to the first wavelength λ1.
[0049] In the second step of the method for manufacturing DOE 10, a protrusion 24 is formed on the dielectric layer 18. In an example of a preferred embodiment herein, the protrusion is a rotationally symmetric protrusion formed at the junction between the dielectric layer 18 and the absorber layer 16. The axis of rotation 26 of the rotationally symmetric protrusion 24 is perpendicular to the absorber layer 16. Figure 1 As can be seen, in this case, the dielectric layer 18 does not abut against the absorption layer 16 at the protrusion 24, but is separated from the absorption layer 16 at the protrusion 24. The cavity 28 is located at the protrusion 24 between the dielectric layer 18 and the absorption layer 16. The protrusion 24 has a Gaussian shape relative to the plane in a cross-section passing through the protrusion 24 along a plane perpendicular to the absorption layer 16.
[0050] In the example of the preferred embodiment herein, the substrate 14 of the laser mirror 12 and thus the substrate of the DOE 10 are made of quartz glass, and the absorption layer 16 is made of amorphous silicon. Furthermore, in this embodiment, the layer thickness 30 of the absorption layer is 40 nm. Layer thickness 30 refers to the dimension of the absorption layer 28 perpendicular to its extension.
[0051] The protrusions 24 of the dielectric layer 18 are formed by a series of focused heating laser beams 38 with a second wavelength λ2 (only when...). Figure 2 (As shown in the diagram) The heat input 54 of the heated laser beam 38 in the absorption layer 16 of a given volume of the laser mirror 12, generated by processing the laser mirror 12, is greater than 30 kJ / cm². 3 Therefore, at least one of the resulting protrusions 24 has a height 32 that is at least half the height of the first wavelength λ1. Thus, the present invention has at least one protrusion 24 with a height 32 of at least 266 nm.
[0052] Figure 2An apparatus 34 for performing a method of manufacturing DOE 10 is schematically shown. The apparatus 34 includes a heating laser 36 for generating a heated laser beam 38 having a second wavelength λ2, a focusing device 40 for focusing the heated laser beam 38, a laser mirror positioning device 42, and a controller 44. In an example of a preferred embodiment herein, the heating laser 36 generates a second wavelength λ2 of 532 nm. The apparatus 34 also includes a deflection device 46 for deflecting the heated laser beam 38. In this case, this is achieved using a one-dimensional galvanometer scanner 46, which is designed to deflect the heated laser beam 38 in one direction. Figure 2 In this configuration, the direction of the heated laser beam 38 to the laser mirror 12 corresponds to the z-direction. The galvanometer scanner 46 allows the heated laser beam 38 to be deflected in the x-direction. Furthermore, the device 34 includes an acousto-optic modulator 52, which can change the intensity of the heated laser beam 38 and thus its power.
[0053] In order to generate the grid-like arrangement of the protrusions 24 of the dielectric layer 18 by means of this device, the laser mirror positioning device 42 is designed to allow the laser mirror 12 to be displaced. Here, the displacement direction of the laser mirror 12 is the y-direction, that is, the direction perpendicular to the heating laser beam 38 and the deflection direction of the galvanometer scanner 46.
[0054] In addition, the controller is designed to actuate the heating laser 36, the acousto-optic modulator 52, the deflection device 46, and the laser mirror positioning device 42.
[0055] Furthermore, in the example of the preferred embodiment herein, the focusing device 40 for focusing the heated laser beam 38 is implemented using a confocal microscope. A confocal microscope (f Objektiv =2cm; f Tubus =f2=30cm) The heated laser beam 38 is focused onto the absorption layer 16.
[0056] The heated laser 36, focusing device 40, laser mirror positioning device 42, and deflection device 46 are arranged relative to each other by means of a mirror 50 and a lens 48, such that the heated laser beam 38 strikes the absorption layer 16 of the laser mirror perpendicularly. The heated laser beam 38 strikes the rear side of the laser mirror 12 and penetrates the substrate 14 to reach the absorption layer 16. The absorption of the heated laser beam 38 results in at least 30 kJ / cm² in the absorption layer 16. 3 The localized heat input 54 leads to the formation of protrusion 24.
[0057] List of reference numerals
[0058] 10. Diffractive optical elements, DOE
[0059] 12 Laser Mirrors
[0060] 14 substrate
[0061] 16 Absorption Layer
[0062] 18 dielectric layers
[0063] 20. Material layer made of the first material
[0064] 22. Material layer made of a second material
[0065] 24 Protrusions
[0066] 26. Axis of rotation
[0067] 28 cavities
[0068] 30. Layer thickness of the absorption layer
[0069] 32. Height of the protrusion
[0070] 34 devices
[0071] 36 Heated Laser
[0072] 38 Heating laser beam
[0073] 40 Focusing device, confocal microscope
[0074] 42. Laser mirror positioning device, positioning stage
[0075] 44 Controller
[0076] 46. Deflection device, galvanometer scanner
[0077] 48 Lenses
[0078] 50 mirrors
[0079] 52 Acousto-optic modulator
[0080] 54 heat input
Claims
1. A method for manufacturing a diffractive optical element (10) for beam shaping a laser beam having a first wavelength (λ1) of at least 100 nm, the method comprising the steps of: - Provide laser mirror (12). The laser mirror (12) has a layered structure made of a substrate (14) and a dielectric layer (18), with the dielectric layer (18) abutting against the substrate (14). Alternatively, the laser mirror (12) has a layered structure made of a substrate (14), a dielectric layer (18), and an absorption layer (16), with the absorption layer (16) located between the substrate (14) and the dielectric layer (18). The dielectric layer comprises multiple layers with different refractive indices. - By processing the laser mirror (12) with a series of focused heated laser beams (38) having a second wavelength (λ2), a plurality of protrusions (24) of the dielectric layer (18) are generated, wherein the plurality of protrusions are formed directly in situ by the heated laser beams without adding any additional material or removing any material from the laser mirror. The plurality of protrusions (24) have a height (32) perpendicular to the dielectric layer (18), and the height (32) of at least one protrusion is at least half of the first wavelength (λ1), wherein the layered structure of the dielectric layer is maintained for the protrusion, and The resulting protrusions are permanent protrusions, which remain in the dielectric layer even after the heating laser beam is no longer applied.
2. The method according to claim 1, wherein the provided laser mirror and diffractive optical element have a T≤10 for the first wavelength (λ1). -2 Transmittance.
3. The method according to claim 1 or 2, wherein the absorber layer (16) is composed of silicon or gold, the substrate (14) is composed of glass, CaF2, MgF2 or sapphire, and / or the dielectric layer (18) is composed of SiO2, Ta2O5, TiO2, HfO2, Al2O3, MgF2, LaF3 and / or ZrO2.
4. The method according to claim 1 or 2, wherein when the laser mirror (12) is processed with a series of focused heated laser beams (38), the heat input from the heated laser beams (38) into the volume of the dielectric layer (18) or the absorption layer (16) of the laser mirror (12) is at least 30 kJ / cm². 3 .
5. The method according to claim 1 or 2, wherein when the laser mirror (12) is treated with a series of focused heated laser beams (38), the second wavelength (λ2), the power of the heated laser beams (38), the focusing of the heated laser beams (38), the heating duration, the absorption layer (16) of the laser mirror (12), the dielectric layer (18) of the laser mirror (12) and / or the layer thickness (30) of the absorption layer (16) are selected such that at least one protrusion (24) has a height (32) of at least half of the first wavelength (λ1).
6. The method according to claim 1 or 2, wherein the thickness of the absorption layer (16) is greater than 30 nm.
7. The method according to claim 1 or 2, wherein when the laser mirror (12) is treated with a series of focused heated laser beams (38), the second wavelength (λ2) is between 200 and 700 nm and the absorption layer (16) of the laser mirror (12) is made of silicon.
8. The method according to claim 1 or 2, wherein when the laser mirror (12) is treated with a series of focused heated laser beams (38), the second wavelength (λ2) is between 200 and 2000 nm and the absorption layer (16) of the laser mirror (12) is made of gold.
9. The method according to claim 1 or 2, wherein when the laser mirror (12) is treated with a series of focused heated laser beams (38), the second wavelength (λ2) is between 100 and 2000 nm.
10. The method according to claim 1 or 2, wherein when the laser mirror (12) is processed with a series of focused heated laser beams (38), the power of the heated laser beams (38) is at least 10 mW.
11. The method according to claim 1 or 2, wherein when the laser mirror (12) is processed with a series of focused heated laser beams (38), the heated laser beams (38) are focused onto the absorption layer (16) and / or the dielectric layer (18), which have a full width at half maximum (FWHM) of up to 5 μm.
12. The method according to claim 1 or 2, wherein when the laser mirror (12) is treated with a series of focused heated laser beams (38), the heating duration of the heated laser beams is between 1 μs and 1 ms.
13. The method according to claim 1 or 2, wherein when the laser mirror (12) is processed with a series of focused heated laser beams (38), the laser mirror (12) is displaced along a displacement direction perpendicular to the heated laser beams (38) during the processing, and the heated laser beams (38) are deflected perpendicular to the displacement direction during the processing, or the laser mirror (12) is displaced along two mutually orthogonal displacement directions during the processing, both of which are perpendicular to the heated laser beams (38).
14. A diffractive optical element (10) for beam shaping a laser beam having a first wavelength (λ1) of at least 100 nm, the beam shaping of the laser beam having the first wavelength (λ1) occurring by reflection of the laser beam on the diffractive optical element (10), the diffractive optical element (10) having a layered structure made of a substrate (14), a dielectric layer (18) and an absorption layer (16), the absorption layer (16) being located between the substrate (14) and the dielectric layer (18), the absorption layer (16) being designed to absorb a heated laser beam (38) when heat is generated input to the absorption layer (16), wherein the dielectric layer comprises a layered structure having multiple layers with different refractive indices. The dielectric layer (18) has a plurality of protrusions (24), wherein the plurality of protrusions are formed in situ directly by a series of focused heated laser beams having a second wavelength without adding any additional material or removing any material from the laser mirror, the protrusions (24) having a height (32) perpendicular to the dielectric layer (18), and at least one protrusion (24) having a height (32) of at least half of the first wavelength (λ1), wherein the layered structure of the dielectric layer is maintained for the protrusions, and wherein the protrusions formed are permanent protrusions that remain in the dielectric layer after the heated laser beams are no longer applied.
15. An apparatus (34) for performing the method according to any one of claims 1 to 13, the apparatus (34) comprising a heating laser (36) for generating a heated laser beam (38) having a second wavelength (λ2), a laser mirror positioning device (42) for providing a laser mirror (12), a focusing device (40) for focusing the heated laser beam (38) onto the laser mirror (12), a deflection device (46) and a controller (44), the laser mirror positioning device (42) being designed to displace the laser mirror (12) in a displacement direction, the deflection device being designed to deflect the heated laser beam (38) perpendicular to the displacement direction, and the controller being designed to actuate the heating laser (36), the deflection device (46) and the laser mirror positioning device (42).