Apparatus for generating a periodic structure in a substrate surface of a substrate and method for the operation thereof
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- INST FUR NANOPHOTONIK GOETTINGEN EV
- Filing Date
- 2024-08-02
- Publication Date
- 2026-07-08
Smart Images
Figure EP2024072034_06032025_PF_FP_ABST
Abstract
Description
[0001] Device for producing a periodic structure in a substrate surface of a substrate and method for its operation
[0002] Description
[0003] Field of the invention
[0004] The invention relates to a device for producing a periodic structure in a substrate surface of a substrate, wherein the substrate surface can be positioned in a processing plane of the device, comprising
[0005] - a laser source for generating an illumination beam,
[0006] - a 2-grating beam splitter, which combines two parallel oriented, diffractive
[0007] Line grating and by means of which the illumination beam can be split into a plurality of partial beams,
[0008] - a controllable beam deflection device, by means of which an input surface of the 2-grating beam splitter can be scanned with the illumination beam,
[0009] - a focusing optics, by means of which the partial beams can be focused in the area of the processing plane,
[0010] - an imaging optics by means of which the beam deflection device can be imaged into the entrance pupil of the focusing optics, and
[0011] - Conditioning means, by means of which it can be ensured that the illumination beam falls collimated onto the input surface of the 2-grating beam splitter.
[0012] The invention further relates to a method for producing a periodic structure in a substrate surface of a substrate by means of such a device, comprising the steps:
[0013] Positioning the substrate surface in the processing plane of the device,
[0014] Applying the illumination beam to the beam deflection device and - controlling the beam deflection device in such a way that an area of the substrate surface to be processed is scanned by a light spot generated by the focusing optics, wherein the intensity of the illumination beam is adjusted in such a way that the fluence of the light spot is partially above a reaction threshold of the substrate surface, so that a periodic structure is generated in the substrate surface.
[0015] State of the art
[0016] Such a device and such a method are known from DE 102008 038 591 B3.
[0017] Security holograms with typical structural periods around 1 pm have become firmly established for the counterfeit-proof marking of objects such as banknotes, payment cards, identification documents, packaging, etc. With appropriate illumination of such a miniaturized hologram, predefined images become visible to the observer at specified angles. These can be compared with expected values, with any discrepancies detected indicating counterfeits. A high degree of complexity can be achieved through superimposed and nested coding of the images in the hologram, which, despite the fundamental technical difficulty of creating such holograms, ensures a high degree of counterfeit security.
[0018] Laser writing processes are very flexible methods for producing such holograms. For example, DE 10 2010 029 321 B4 or
[0019] DE 102006 032 053 B4 discloses methods in which the substrate surface of a substrate, for example a glass, a ceramic, a plastic or similar, is irradiated with a writing spot of a laser, wherein the intensity of the writing spot exhibits a periodic spatial modulation. With correct adjustment, the fluence in the "bright" areas of this periodic structure exceeds a reaction threshold of the substrate surface, which then changes optically perceptibly there, while it remains unchanged in the "dark" areas of lower fluence. For example, this can be a photochemical reaction, an ablation or a similar, fluence-dependent surface modification. Although the aforementioned publications only describe the modification of an outer surface of the substrate, the term "substrate surface" in the context of the present description is generally to be understood broadly and includes any optically accessible surface of a substrate, i.e.in particular external surfaces and internal surfaces of transparent substrates.
[0020] In order to provide a larger area with the said periodic structure, a writing area of the substrate surface can be scanned with the said writing spot. If this is done using one of the devices as described in the aforementioned publications, the period, phase position, and orientation of the generated structure do not change during scanning. Therefore, a large-area, uniform structure can be created. On the other hand, by changing the mechanical parameters of the device during the scanning process, it is possible to specifically create local variations in the period, phase position, and / or orientation of the structure. In this way, large-area "mosaics" can be constructed from differently structured "tiles." Due to the relatively large writing spot size, structures generated with the previously known devices typically have a spatial resolution of 10 pm and greater. However, a higher resolution would be desirable, i.e.the creation of smaller "tiles." In the known devices, scaling toward smaller writing spots is counteracted by the associated increasing astigmatic distortion.
[0021] From the aforementioned generic document DE 102008 038 591 B3, a device is also known with which a large-area mosaic of differently structured "tiles" can be created using a raster process by exposing a substrate surface to a laser illumination beam. The core of this device is a 2-grating beam splitter consisting of two diffractive line gratings arranged parallel to each other with respect to their grating surfaces. The grating lines of the two line gratings are oriented perpendicular to each other. The illumination beam of a laser source is split into several partial beams by means of this 2-grating beam splitter, which are then superimposed in the processing plane with interference by means of a Schwarzschild lens, which focuses each individual partial beam separately in a focal plane shortly before the processing plane.This interference creates a periodic fluence distribution within the writing spot on the substrate surface, which, with correct adjustment of the intensity of the illumination beam, leads to the periodic structuring of the substrate surface described above. The scanning required to form a large-area structure is achieved by means of a beam deflection device designed as a pivoting mirror, which is imaged into the entrance pupil of the Schwarzschild objective by means of a field lens arranged in front of the 2-grating beam splitter and acting as imaging optics. In the context of this description, the term entrance pupil refers to the area of the rear focal plane of an optical system that is defined by its entrance aperture (which can be determined, for example, by the lens diameter or a lens mount).In the case of microscope lenses, one often refers to the exit pupil because the direction of light transmission is usually reversed compared to the current field of technology. A conditioning optics system positioned upstream of the pivoting mirror first expands the illumination beam and then focuses it in the back focal plane of the field lens. While this known device can be used to create very complex structures on the substrate surface, the size of the writing spot is also limited. Furthermore, this known technique is limited to the processing of external substrate surfaces due to the focusing system positioned upstream of the processing plane.
[0022] DE 103 28 314 A1 describes the use of a so-called diffractive delay generator, consisting of two diffraction gratings arranged one behind the other and parallel to each other, as a beam splitter within a device for generating beams with a selective phase relationship. In one described variant, the grating lines of the two diffraction gratings are oriented at an angle to each other or crossed to achieve a better selection of individual partial beams.
[0023] From DE 196 04 907 A1 a Michelson interferometer is known which has a pair of parallel aligned phase gratings with identical grating parameters as a beam splitter.
[0024] DE 195 38 747 A1 describes a pair of parallel phase gratings with parallel grating lines as part of a method for determining wave aberrations of plane waves using a so-called grating shear interferometer. DE 102013 004 869 A1 discloses a device for periodically structuring a surface using a laser beam. The collimated laser beam is passed through an arrangement consisting of a diffraction grating and a prism, resulting in parallel partial beams that interfere with each other on the surface to be treated by means of a downstream focusing optics.
[0025] EP 3 341 153 B1 also discloses a device for the ablative production of a periodic line structure on a workpiece, in which the collimated beam of a laser is split into partial beams at a phase mask while suppressing the zeroth diffraction order, the phase mask being imaged onto the workpiece surface to be machined by means of a cylindrical lens.
[0026] Task
[0027] The object of the present invention is to further develop a device of this type in such a way that smaller write spot sizes can be achieved. It is also an object of the present invention to provide a method for operating such a device that is suitable for producing highly complex structures in the substrate surface.
[0028] Description of the invention
[0029] The above-mentioned first object is achieved in conjunction with the features of the preamble of claim 1 in that the grating lines of the two line gratings are aligned parallel to each other and the focusing optics are configured to focus the partial beams in the processing plane.
[0030] The second object mentioned above is achieved in conjunction with the features of the preamble of claim 12 in that
[0031] - by rotating the 2-grating beam splitter around its optical axis, an angular orientation of the periodic structure is locally varied,
[0032] - by varying the distance between the diffractive line gratings of the 2-grating beam splitter, the period of the periodic structure is varied locally and / or - by laterally shifting the diffractive line gratings of the 2-grating beam splitter perpendicular to the longitudinal direction of their grating lines, a local lateral shift of the periodic structure is generated.
[0033] Preferred embodiments are the subject of the dependent claims.
[0034] A key difference between the invention and the prior art of the same type is that the partial beams generated by the two-grating beam splitter for interfering superposition are not imaged onto the substrate surface or into the processing plane, but are focused there. This allows, on the one hand, a reduction in the writing spot size. On the other hand, it becomes possible to write a periodic pattern onto the inner surfaces of a transparent substrate. This was not previously possible because the laser-induced material changes, which occur at least in the areas of maximum fluence, i.e., at least in the focus, already occurred before the processing plane, but no pattern formation occurred there due to interference.
[0035] To enable the focusing according to the invention, however, a special design of the illumination beam is required beforehand. In particular, it must be collimated, i.e., enter the 2-grating beam splitter as a parallel bundle of rays. At the first grating, the beam is split into further collimated partial beams. At the second grating, whose grating lines are aligned parallel to the grating lines of the first grating, in contrast to the prior art, the partial beams traveling in different directions are deflected so that they run parallel to one another—each still individually collimated. In other words, the 2-grating beam splitter transforms the collimated illumination beam into a bundle of parallel, each collimated partial beams. Their further treatment depends on the specific embodiment of the invention.
[0036] In a first variant, the imaging optics are arranged in front of the 2-grating beam splitter, with the processing plane located in the output focal plane of the focusing optics. In this variant, the partial beams generated by the 2-grating beam splitter enter the focusing optics parallel and collimated, which consequently focuses each individual partial beam in its focal plane and simultaneously superimposes the different partial beams at a common focal point, interfering with each other. The structure-forming interference thus occurs in a writing spot, the size of which is determined by the diameter of the respective partial beams and the focal length of the focusing optics. This corresponds to the theoretically possible miniaturization of the writing spot.
[0037] In a second variant, however, the imaging optics are arranged behind the 2-grating beam splitter, with the output focal plane of the imaging optics lying in an object plane of the focusing optics and the processing plane lying in an image plane of the focusing optics conjugate to said object plane of the focusing optics. In this variant, the partial beams generated by the 2-grating beam splitter enter the imaging optics parallel and collimated, which consequently focuses each individual partial beam in its focal plane and simultaneously superimposes the different partial beams at a common focal point. In this case, the focusing optics serve to image the output focal plane of the imaging optics and thus to image the superimposed focus of the partial beams into the processing plane. This is then, of course, no longer identical to the focal plane of the focusing optics.Nevertheless—and this is the only important aspect—focusing and interfering superposition of the partial beams takes place in the processing plane. An advantage of this variant is that separate conditioning optics, which, in conjunction with the imaging optics (whose primary task is to image the beam deflection device into the entrance pupil of the focusing optics), ensure the collimated incidence of the illumination beam into the 2-grating beam splitter, are no longer required. This is the case, at least in cases where the laser source already provides a collimated illumination beam.
[0038] The gratings of the 2-grating beam splitter are preferably designed as phase gratings, which inherently suppress the generation of a zeroth diffraction order. Such phase gratings are known to those skilled in the art. When using gratings that allow the generation of a zeroth diffraction order, suitable external suppression measures, also known to those skilled in the art, must be taken, for example the provision of optical stops. The partial beams entering the focusing optics parallel and collimated are those that result from "matching" combinations of the diffraction orders at the two gratings. If, for example, both gratings have the same grating period, as preferably provided, these are the partial beams that arise at both gratings in the same diffraction order (with opposite sign) (± 1st order, ± 2nd order, etc.). For other integer period ratios, other combinations of diffraction orders are used.No special measures are required for the selection; rather, partial beam pairs that are not parallel and collimated and enter the focusing optics simply do not lead to the inventive, focused and interfering superposition in the processing plane and therefore have no relevant effect.
[0039] The imaging optics can comprise a converging imaging lens or lens group located immediately upstream or downstream of the 2-grating beam splitter. In many cases, a simple converging field lens will suffice. This is particularly cost-effective. However, embodiments that provide more complex lens arrangements are, of course, not excluded in the context of the present invention. Optical aberrations can be better corrected in this way.
[0040] The beam deflection device is preferably located in an object plane of the imaging lens or lens group, and the focusing optics, in particular their entrance pupil, are located in an imaging plane of the imaging lens or lens group that is conjugate to the object plane of the imaging lens or lens group. This is the ray-optical paraphrase of the functional specification already explained above, according to which the beam deflection device is imaged onto the focusing optics by means of the imaging optics. However, there is a certain, small tolerance range around the rear, i.e., entrance-side, focal plane of the focusing optics, which should be included.
[0041] As already mentioned above, it is essential to the invention that the illumination beam enters the 2-grating beam splitter in a collimated state, so that the resulting partial beams are also collimated and run parallel to one another. Up to now, only general reference has been made to corresponding conditioning means in this regard. In particular in cases of the above-mentioned second variant of the invention, in which the 2-grating beam splitter is arranged between the controllable beam deflection device and the imaging optics, this can be means integrated into the laser source, for example, which ensure that the illumination beam leaves the laser source already collimated. Alternatively, it can be a separate conditioning optics. In the aforementioned case, this can cause beam expansion and simultaneous collimation of the illumination beam before it strikes the beam deflection device.
[0042] However, in cases of the aforementioned first variants, in which the imaging optics are arranged upstream of the 2-grating beam splitter, the use of separate conditioning optics is required in almost every case. The conditioning optics are then preferably arranged upstream of the imaging optics. In particular, they can comprise a converging conditioning lens or lens group arranged upstream and / or downstream of the beam deflection device. For reasons of overall compactness, arranging the conditioning lens or lens group upstream of the beam deflection device is preferred.
[0043] If, as advantageously provided, the distance of the imaging lens or lens group, in particular its principal plane, from the conditioning lens or lens group, in particular its principal plane, corresponds to the sum of their focal lengths, the imaging lens or lens group, on the one hand, and the conditioning lens or lens group, on the other hand, together form a telescope optics in the manner of a Keplerian telescope, which is particularly suitable for sending a beam incident in collimated form into the conditioning optics in a collimated form to the 2-grating beam splitter. In the event that the illumination beam from the laser source is not supplied as a collimated beam, the skilled person will be able to take appropriate corrective measures in the area of the conditioning lens to ensure an overall collimated incidence of the illumination beam into the 2-grating beam splitter.A correction in the area of the imaging optics, however, is considered less advantageous, since this would also affect the imaging of the beam deflection device.
[0044] To locally modify the properties of the structure inscribed on the substrate surface using the device according to the invention, various mechanical measures can be taken during the scanning process, preferably synchronized with it, and / or during a pulsed generation of the illumination beam. For example, the angular orientation of the generated periodic structure can be changed by rotating the 2-grating beam splitter around its optical axis. Applying a different rotationally aligned 2-grating beam splitter to the substrate surface at different positions thus results in structural lines in the substrate surface that are aligned at corresponding angles to one another.
[0045] Varying the spacing between the individual gratings of the two-grating beam splitter, however, leads to a variation in the period of the structure created in the substrate surface. In other words, the generated lines are spaced at different distances from each other.
[0046] Finally, a lateral relative displacement of the individual gratings of the two-grating beam splitter perpendicular to the longitudinal extension of their grating lines leads to a lateral displacement of the periodic structure. In other words, this changes the spatial phase position of the generated periodic structure. A relative displacement parallel to the longitudinal extension of the grating lines, on the other hand, does not result in any change in the generated structure.
[0047] In principle, it is possible to provide a large area on the substrate surface with a continuous, uniform line structure using the device according to the invention. In this respect, the same results can be achieved as with prior art devices. However, if one is interested in constructing a complex structure composed of differently structured "tiles" as a "mosaic," this is possible based on the present invention using significantly smaller "tiles" than was possible with the prior art. This is due to the miniaturized writing spot according to the invention.
[0048] Further details and advantages of the invention will become apparent from the following specific description and drawings.
[0049] Short description of the drawing
[0050] They show:
[0051] Figure 1: a schematic representation of the beam path of a first
[0052] Embodiment of a device according to the invention and Figure 2: a schematic representation of the beam path of a second
[0053] Embodiment of a device according to the invention.
[0054] Description of preferred embodiments
[0055] The same reference numerals in the figures indicate the same or analogous elements.
[0056] Figure 1 shows a schematic, ray-optical representation of a preferred embodiment of a device 10 according to the invention with an optical axis 11 for producing a periodic structure in the substrate surface 121 of a substrate 12. The substrate 12 is fixed in a holder (not shown in detail) such that its substrate surface 121 lies in a processing plane 101 of the device 10.
[0057] An illumination beam 14 is generated by a laser source (not shown), which in the illustrated embodiment is provided as a collimated beam. The illumination beam 14 is preferably a pulsed laser beam. However, this is not essential to the invention. Other parameters of the illumination beam, such as in particular its wavelength and intensity, are matched to the properties of the substrate. The person skilled in the art will have to ensure in each individual case that the properties of the illumination beam as a whole are suitable for inducing the desired structuring reaction in the substrate surface.
[0058] The illumination beam 14 then passes through a conditioning optics 16, which in the illustrated embodiment is designed as a simple converging lens with a focal length f1. This focuses the illumination beam 14 in the front, i.e. output-side focal plane 161 of the conditioning optics 16. Behind this focal plane 161 is arranged an imaging optics 18, which in the illustrated embodiment is also designed as a simple converging lens, specifically with a focal length f2. It is arranged in the beam path such that its input-side focal plane 182 coincides with the output-side focal plane 161 of the conditioning optics 16. Both optics 16, 18 together therefore form a Keplerian telescope, which the illumination beam leaves again collimated after being focused in the common focal plane 161, 182 of the conditioning optics 16 and the imaging optics 18.At the same time, the imaging optics 18 with its output-side focal plane 181 and its input-side focal plane 182 forms an independent imaging system for the beam deflection device 24 to be described further below.
[0059] The (re-)collimated illumination beam 14 then impinges on the input grating 201 of a two-grating beam splitter 20. The input grating 201 is designed as a diffractive line grating. Here, the illumination beam 14 is split into still-collimated partial beams 141, which propagate in different directions according to their diffraction order. The partial beams 141 then impinge on the output grating 202 of the two-grating beam splitter 20. This is also designed as a line grating, the grating lines of which are oriented, in particular, parallel to the grating lines of the input grating 201. Their grating spacing is also preferably equal to the grating spacing of the grating lines of the input grating 201. At the output grating 202, the partial beams 141 undergo a further deflection and leave the 2-grating beam splitter as partial beams 14T that are still collimated but now parallelized, ie parallel to each other.
[0060] These beams impinge on the entrance pupil of a focusing optic 22, which in the illustrated embodiment is designed as a microscope objective. Due to their collimated and mutually parallel nature, each of the partial beams 14T, as well as all parallel partial beams 14T, are focused at the same point in the output-side focal plane 221 of the focusing optic 22. This output-side focal plane 221 of the focusing optic 22 coincides with the processing plane 101 of the device 10 and therefore with the substrate surface 121 of the substrate 12 to be processed.
[0061] In order to be able to structure a larger area on the substrate surface 121, the substrate surface 121 must be scanned with the writing spot, i.e. the point of superposition of the partial beams 14T explained above. For this purpose, a beam pivoting device 24 is provided, which in the illustrated embodiment is designed as a pivoting mirror. However, other mechanical and / or electro-optical units generally known to those skilled in the art would also be conceivable. In the illustrated embodiment, the beam pivoting device 24 is arranged between the conditioning optics 16 and the imaging optics 18. In any case, however, the beam pivoting device 24, the imaging optics 18 and the focusing optics 22 must be arranged relative to one another such that the beam pivoting device 24 is imaged by means of the imaging optics 18 into the entrance pupil in the entrance-side focal plane 222 of the focusing optics 22.The latter must therefore lie in an image plane 183 of the imaging optics 18, which is conjugate to the object plane 184 of the imaging optics 18, in which the beam deflection device 24 is arranged. The ray-optical representation of this image is shown in dotted lines in Figure 1.
[0062] Figure 2 shows an embodiment in which the imaging optics 18 are arranged behind the 2-grating beam splitter 20. In the embodiment shown, the illumination beam 14 impinges on the beam deflection device 24 in a collimated state. It is not clear whether this collimation is generated by a separate collimating optics (not shown in Figure 2) or by collimating means integrated into the laser source (also not shown). Here, too, the illumination beam 14 impinges on the input grating 201 of the 2-grating beam splitter 20 in a collimated state and is split, as described above, into partial beams 141 and 14T, respectively.
[0063] The collimated and parallelized partial beams 14T fall on the imaging optics 18 and are focused in its output-side focal plane 181 and superimposed on one another. In this embodiment, the focusing optics 22, which follows in the beam path, serves to image this output-side focal plane 181 of the imaging optics 18 into the processing plane 101, in which the substrate surface 121 to be processed is located. The output-side focal plane 181 of the imaging optics 18 thus corresponds to an object plane 224 of the focusing optics 22, which is conjugated to an image plane 223 of the focusing optics 22, which coincides with the processing plane 101 or substrate surface 121.
[0064] With regard to the imaging of the beam deflection device 24 into the input-side focal plane of the focusing optics, in particular into its entrance pupil, by means of the imaging optics 18, which is of course also required in this embodiment, reference can be made in full to the corresponding explanations for the embodiment of Figure 1. Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative embodiments of the present invention. A broad spectrum of possible variations is available to the person skilled in the art in light of the disclosure here. In particular, the imaging optics 18 and the conditioning optics 16 can also be designed as more complex lens groups instead of simple field lenses. In particular, the conditioning optics 16 can be arranged entirely or, if designed as a lens group, partially behind the beam deflection device 24.
[0065] List of reference symbols
[0066] 10 Device
[0067] 101 Editing level
[0068] 11 optical axis
[0069] 12 Substrat
[0070] 121 substrate area
[0071] 14 Illumination beam
[0072] 141 partial beam
[0073] 14T parallelized partial beams
[0074] 16 Conditioning optics
[0075] 161 output focal plane of 18
[0076] 18 Imaging optics
[0077] 181 output focal plane of 18
[0078] 182 input-side focal plane of 18
[0079] 183 Image plane
[0080] 184 Object Level
[0081] 20 2-grating beam splitters
[0082] 201 entrance grilles of 20
[0083] 202 output grids of 20
[0084] 22 Focusing optics
[0085] 221 output focal plane of 22
[0086] 222 input-side focal plane of 22
[0087] 223 Image plane
[0088] 224 Object Level
[0089] 24 Beam deflection device f1 focal length of 16 f2 focal length of 18
Claims
Patent claims 1. Device (10) for generating a periodic structure in a Substrate surface (121) of a substrate (12), wherein the substrate surface (121) is positionable in a processing plane (101) of the device (10), comprising - a laser source for generating an illumination beam (14), - a 2-grating beam splitter (20) comprising two diffractive line gratings oriented parallel to one another and by means of which the illumination beam (14) can be split into a plurality of partial beams (141, 14T), - a controllable beam deflection device (24) by means of which an input surface of the 2-grating beam splitter (20) can be scanned with the illumination beam (14), - a focusing optics (22) by means of which the partial beams (14T) can be focused in the area of the processing plane (101), - an imaging optic (18) by means of which the beam deflection device (24) can be imaged into the entrance pupil of the focusing optics (22), and - Conditioning means by means of which it can be ensured that the illumination beam (16) falls collimated onto the input surface of the 2-grating beam splitter (20), characterized in that the grating lines of the two line gratings are aligned parallel to one another and the focusing optics (22) are designed to focus the partial beams (14T) in the processing plane (101).
2. Device (10) according to claim 1, characterized in that the imaging optics (18) are arranged in front of the 2-grating beam splitter (20), wherein the processing plane (101) lies in the output-side focal plane (221) of the focusing optics (22).
3. Device (10) according to claim 2, characterized in that the imaging optics (18) comprises a collecting imaging lens or lens group immediately upstream of the 2-grating beam splitter (20).
4. Device (10) according to one of the preceding claims, characterized in that the imaging optics (18) are arranged behind the 2-grating beam splitter (20), wherein the output-side focal plane (181) of the imaging optics (18) lies in an object plane (224) of the focusing optics (22) and the processing plane (101) lies in an image plane (223) of the focusing optics (22) conjugated to said object plane (224) of the focusing optics (22).
5. Device (10) according to claim 4, characterized in that the imaging optics (18) comprises a collecting imaging lens or lens group immediately downstream of the 2-grating beam splitter (20).
6. Device (10) according to one of claims 3 or 5, characterized in that the beam pivoting device (24) lies in an object plane (184) of the imaging lens or lens group and the entrance pupil of the focusing optics (22) lies in an image plane (183) of the imaging lens or lens group conjugated to said object plane (184) of the imaging lens or lens group.
7. Device (10) according to one of the preceding claims, characterized in that the conditioning means are designed as a separate conditioning optics (16) which is arranged in front of the imaging optics (18).
8. Device (10) according to claim 7, characterized in that the conditioning optics (16) comprises a converging conditioning lens or lens group arranged in front of and / or behind the beam deflection device (24).
9. Device (10) according to claim 8 and one of claims 3 or 5, as far as dependent on claim 3, characterized in that the distance of the imaging lens or lens group from the conditioning lens or lens group corresponds to the sum of their focal lengths (f 1 , f2).
10. Device (10) according to one of the preceding claims, characterized in that the grating periods of the line gratings are in an integer ratio to one another, in particular are equal.
11. Device (10) according to one of the preceding claims, characterized in that each of the line gratings is designed as a phase grating suppressing the respective zeroth diffraction order.
12. A method for producing a periodic structure in a substrate surface (121) of a substrate (12) by means of a device (10) according to one of the preceding claims, comprising the steps: - positioning the substrate surface (121) in the processing plane (101) of the device (10), - applying the illumination beam (14) to the beam deflection device (24) and - controlling the beam deflection device (24) in such a way that an area of the substrate surface (121) to be processed is scanned by a light spot generated by the focusing optics (22), wherein the intensity of the illumination beam (14) is adjusted such that the fluence of the light spot is partially above a reaction threshold of the substrate surface (121), so that a periodic structure is produced in the substrate surface (121), characterized in that - by rotating the 2-grating beam splitter (20) around its optical axis (11), an angular orientation of the periodic structure is locally varied, - by varying the distance between the diffractive line gratings of the 2-grating beam splitter (20) the period of the periodic structure is varied locally and / or - a local lateral displacement of the periodic structure is generated by lateral displacement of the diffractive line gratings of the 2-grating beam splitter (20) perpendicular to the longitudinal direction of their grating lines.