WO2021110297A1

WO2021110297A1 - Device for illuminating a workpiece, method for modifying same, and method for measuring the surface of the workpiece

Info

Publication number: WO2021110297A1
Application number: PCT/EP2020/075736
Authority: WO
Inventors: Peter Simon
Original assignee: Institut Für Nanophotonik Göttingen E.V.
Priority date: 2019-12-04
Filing date: 2020-09-15
Publication date: 2021-06-10
Also published as: DE102019133009B4; DE102019133009A1

Abstract

The invention relates to a device for illuminating a workpiece with an interference pattern, comprising a two-grating interferometer (10) that has two mutually spaced diffraction gratings (11, 12), namely an input-side diffraction grating (11) and an output-side diffraction grating (12), aligned perpendicularly to the optical axis of the interferometer in order to generate diffraction beams (21, 22), which run along different beam paths on a common diffraction plane and which overlap with each other on an interference pattern plane (40) so as to produce interference, by diffracting an input beam (21) at the input-side diffraction grating (11) and diffracting the resulting diffraction beams (21, 22) again at the output-side diffraction grating (12), wherein identical beam modification elements, which can be tilted about tilting axes oriented perpendicularly to the diffraction plane in a synchronized and mirror-symmetrical manner, are arranged at mirror-symmetrical positions in the beam paths of the diffraction beams (21, 22). The invention is characterized in that the beam modification elements are designed as plane-parallel panels (31, 32). The invention additionally relates to a processing and measuring method using such an illumination device.

Description

Device for illuminating a workpiece, method for its modification and method for measuring its surface

description

Field of invention

The invention relates to a device for illuminating a workpiece with an interference pattern, comprising a two-grating interferometer, which has two diffraction grids aligned perpendicular to its optical axis and arranged at a distance from one another, namely an input-side and an output-side diffraction grating, for generating along different beam paths Diffraction rays that run in a common diffraction plane and interfere with each other in an interference pattern plane are caused by diffraction of an input beam in the diffraction grating on the input side and renewed diffraction of the diffraction rays resulting on the diffraction grating on the output side, with tilt axes aligned in mirror-symmetrical positions in the beam paths of the diffraction beams of the same type, in order to be mirror-symmetrical, tilting axes that are synchronized perpendicular to the diffraction grating Beam modification elements are arranged.

The invention further relates to a method for modifying a workpiece by means of a two-grating interferometer with an input-side and an output-side diffraction grating, comprising the steps:

- Generation of diffraction beams running along different beam paths in a common diffraction plane by diffraction of a pulsed input beam at the diffraction grating on the input side and

- Generation of an interference pattern in a processing plane of the workpiece by superimposing the diffraction beams by means of their renewed diffraction at the diffraction grating on the output side, The input beam is pivoted in a manner synchronized with its pulse rate in order to illuminate different areas of the processing plane with the interference pattern, and with mirror-symmetrical beam modification elements of the same type at mirror-symmetrical positions in the beam paths of the diffraction beams about tilt axes aligned perpendicular to the diffraction plane in a manner synchronized with the input beam pulses be tilted.

The invention finally relates to a method for measuring a workpiece surface by means of a two-grating interferometer with an input-side and an output-side diffraction grating, comprising the steps:

- Generation of diffraction beams running along different beam paths in a common diffraction plane, initially diverging and then again converging towards a common geometric intersection point by bending an input beam at the entrance-side diffraction grating and renewed diffraction of the resulting diffraction rays at the exit-side diffraction grating,

- Determining the perpendicular distance between the workpiece surface and the geometric intersection of the diffraction rays, wherein the determination of said perpendicular distance comprises varying the same,

Calculation of a local surface height value from the determined vertical distance, the input beam being swiveled over the workpiece surface in order to obtain the assigned local surface height values for a plurality of points on the workpiece surface by repeating the aforementioned steps.

State of the art

A generic lighting device and a generic workpiece modification method are known from US Pat. No. 6,904201 B1.

From DE 102006032 053 A1 a so-called two-grating interferometer for illuminating a workpiece with an interference pattern and - with a suitable setting of the fluence of the interference pattern - for corresponding modification of the workpiece, in particular its surface, is known. A two-grating interferometer consists essentially of two parallel diffraction gratings which are spaced apart from one another and whose identically aligned grating lines are in a period ratio to one another known to the person skilled in the art and generally described in the aforementioned publication. An input beam impinging on the diffraction grating on the input side is diffracted into partial beams of different diffraction orders, each with a positive and negative sign. The two partial beams with different signs of a selected diffraction order diverge along diverging beam paths within a common plane, referred to here as the diffraction plane. So they hit the second diffraction grating, where they again experience diffraction in partial beams of different diffraction orders, each with a positive and a negative sign. In particular, there are partial beams running along converging beam paths in the diffraction plane, which overlap in an interfering manner at a distance behind the diffraction grating on the exit side, which corresponds to the distance between the diffraction gratings. In a region of this plane, referred to here as the interference pattern plane, which is dependent on the beam width, an interference pattern arises with a periodic distribution of intensity maxima and minima. A workpiece lying in this interference pattern plane is illuminated accordingly. If the fluence of the interference pattern in the areas of its intensity maxima is above a material modification threshold of the workpiece material and if the fluence of the interference pattern in the areas of its intensity minima is below said material modification threshold, a correspondingly patterned modification of the workpiece takes place in the interference pattern plane, which in this context is then referred to as the processing plane can be. The material modification achieved can consist, for example, in an ablation. In this case, the workpiece surface is typically divided into the interference pattern or

Machining plane placed. In the case of transparent materials, however, it is also possible to place a deeper area of the workpiece at a finite distance from the workpiece surface in the interference pattern or processing plane. In these cases, the modification is often associated with a change in the refractive index of the material, for example due to a radiation-induced chemical reaction.

Such a case is described in the generic document mentioned at the beginning. Here, the workpiece to be modified is a light guide, in the core area of which a so-called Bragg grating is inscribed should. In order to be able to inscribe Bragg gratings of different periodicity or a Bragg grating with varying periodicity without changing the diffraction gratings, the document mentioned suggests using a mirror-symmetrical pair of transparent prisms behind the diffraction grating on the output side, each around a tilt axis that is perpendicular to the diffraction plane stands, are tiltable. Due to the influence of these prisms, the periodicity of the interference pattern generated in the interference pattern plane changes as a function of the specifically selected tilt angle of the prisms. In order to provide a longer fiber section with a Bragg grating, the input beam can be swiveled according to the fiber orientation. A special feature of the two-grating interferometer is that the pattern formation and the position of the interference pattern plane are independent of the angle of incidence of the input beam. By means of a tilting of the prisms that is synchronized with the swiveling of the input beam and its pulse rate, a longer fiber section can be provided with a Bragg grating with a periodicity that varies over its length.

A problem that cannot be solved with the generic device arises when - regardless of the question of a varying periodicity of the interference pattern - no essentially one-dimensional workpiece, such as said light guide, but an extended workpiece surface is to be provided with the interference pattern. With a perfectly flat design of the workpiece surface and its alignment exactly perpendicular to the optical axis of the two-grating interferometer, the patterning of the large surface area can be achieved by corresponding two-dimensional pivoting of the input beam. However, if the surface is curved and / or the clamping is not perfectly perpendicular to the optical axis, the interference pattern is mapped in different surface areas above, below or (as optimally provided) exactly on the workpiece surface. This has a significant impact on the sharpness of the pattern written on the workpiece surface. With a known surface shape and / or known misalignment, the problem can theoretically be solved by corresponding tracking of the workpiece parallel to the optical axis. However, the accuracy of this tracking would typically have to be in the range of 10-20 pm, which is hardly possible in practice, especially with regard to the required speeds and weights to be moved. A comparable problem also arises with the use of the two-grating interferometer, which is known in principle to the person skilled in the art, for measuring a curved or not ideally evenly clamped workpiece surface. It is known to illuminate the workpiece surface as described above, but the position of the interference pattern plane, ie that plane in which the geometric intersection of the overlapping diffraction rays lies, relative to the workpiece surface is initially unknown. The diffraction rays reflected back through the second and first diffraction grating along the reversed beam paths from the workpiece surface are then imaged with an image detector, the optics of the image detector being set so that the workpiece surface lies in its depth of field. The recorded image then shows two sharply mapped points, namely the two points of incidence of the diffraction rays on the workpiece surface, the lateral distance of which is directly dependent on the absolute value of the distance between the workpiece surface and the geometric intersection of the diffraction rays. The latter can lie above or below the workpiece surface (whereby it is possible, especially in the second case and in the case of non-transparent workpiece material, that it is not implemented as a real ray intersection at all). Variation of the vertical distance by mechanical lifting or lowering of the workpiece leads to a variation of the lateral distance between the depicted points. If the vertical distance is small, the depicted points merge into a single one. However, it is very difficult to determine the shape of this single depicted point so precisely that the exact superimposition of the points of impact - corresponding to the coincidence of the geometric intersection point and workpiece surface - can be determined with sufficient accuracy. It is therefore customary to adjust the vertical distance, which results in two separately mapped points, the centers of which can be precisely determined by intensity measurements. The vertical distance is then varied by known, vertical, mechanical displacement of the workpiece. From the resulting lateral movement of the imaged points, knowing the geometry of the apparatus, the absolute value (in particular from the lateral point spacing) and the sign (in particular from the direction of movement) of the perpendicular distance between the geometric intersection of the diffraction rays and the workpiece surface are calculated. A major weak point of this approach, however, is the insufficient speed of the mechanical workpiece adjustment. Task

It is the object of the present invention to develop a generic device in such a way that workpieces that are curved and / or clamped at an angle to the optical axis can also be precisely labeled with a continuous interference pattern, or to offer a corresponding workpiece modification method and a corresponding workpiece measurement method.

Statement of the invention

This object is achieved in connection with the features of the preamble of claim 1 in that the beam modification elements are designed as plane-parallel plates.

The object is also achieved in connection with the features of the preamble of claim 5 in that the beam modification elements are designed as plane-parallel plates, the tilting of which sets a predetermined distance between the respectively illuminated area of the processing plane on the one hand and the workpiece surface on the other. In particular, this distance can be “zero”. I. E. The working plane and the workpiece surface coincide in the illuminated area.

The object is further achieved in connection with the features of the preamble of claim 11 in that said variation of the perpendicular distance between the workpiece surface and the geometric intersection of the diffraction beams takes place by mirror-symmetrical and synchronized plane-parallel plates arranged at mirror-symmetrical positions in the beam paths of the diffraction beams about tilt axes aligned perpendicular to the diffraction plane.

The plane-parallel plates, which in their basic position are perpendicular to the respective beam path in which they are introduced, cause a parallel offset of the respective beam when tilted from this basic position. In the diffraction plane, the diffraction rays run in a diamond shape, ie they diverge between the input-side and the output-side diffraction grating and between the diffraction grating on the output side and the interference pattern plane again towards one another. The respective diffraction angles are predetermined by the properties of the respective diffraction grating. These angles therefore remain unchanged regardless of the tilted position of the plane-parallel plates. The parallel offset of the beams in the area between the diffraction gratings and / or behind the diffraction grating on the output side, however, leads to a migration of the intersection of the diffraction beams in the Z direction, ie in the direction of the optical axis of the two-grating interferometer. The intersection of the rays, however, defines the interference pattern plane in which said ray intersection lies and which in turn is perpendicular to the optical axis of the interferometer. The interference pattern forms in the illuminated area of this plane.

In the context of a machining process, as already explained above, the interference pattern plane corresponds to the machining plane of the workpiece. If a curved surface, e.g. the curved workpiece surface, is to be processed over a large area, the "drifting" of the desired processing plane that occurs when the workpiece is scanned from the interference pattern plane specified by the interferometer can be compensated for by tilting this interference pattern plane accordingly by tilting the plane-parallel plates and thus making changes the parallel offset of the diffraction beams is tracked so that it coincides exactly with the desired processing plane at least in the respectively illuminated area. Since, as explained above, the tilting of the plane-parallel plates is only associated with a parallel offset of the diffraction beams and not a change in the angle in the beam path, such tracking does not lead to a change in the period of the interference pattern. Rather, a workpiece can be covered with a continuous pattern projection of uniform periodicity along a curved machining surface, in particular along a curved surface, as was previously only possible in the prior art with exactly flat workpiece surfaces aligned exactly perpendicular to the optical axis.

Two first of the plane-parallel plates are preferably arranged in the area between the diffraction gratings. This position is particularly advantageous because the area behind the diffraction grating on the output side, in which the workpiece is arranged, remains free of additional elements, which generally makes handling of the device easier facilitated. However, the effect according to the invention can also be achieved with first plane-parallel plates arranged behind the diffraction grating on the output side.

In a further development of the invention, which is particularly advantageous in the case of particularly short pulsed input beams, it is provided that two second plane-parallel plates are additionally arranged in the area between the diffraction grating on the output side and the interference pattern plane or the processing plane. It is known that ultrashort pulses are characterized by a broad spectrum of wavelengths. However, different wavelengths are diffracted to different degrees at the diffraction gratings, i.e. they strike the plane-parallel plates at different angles of incidence, which leads to wavelength-dependent parallel offsets there. Since the Z-shift of the interference pattern plane according to the invention is a direct consequence of this parallel offset, this angular dispersion leads to an undesirable wavelength dependence of the position of the interference pattern plane or, in the case of broadband light, to the formation of a "stack" of interference pattern planes according to wavelengths. However, this can be compensated for by the aforementioned arrangement of first plane-parallel plates between the diffraction gratings and second plane-parallel plates behind the diffraction grating on the output side. The first and second plane-parallel plates are preferably tilted by the same angle from their respective basic position. Due to the different alignment of the first and second plane-parallel plates with respect to the upstream diffraction grating, those beam components which have experienced a greater parallel offset on the first plane-parallel plates, a smaller parallel offset on the second plane-parallel plates and vice versa. The parallel offset dispersion is thus compensated. On the other hand, the inventive effect of the interference pattern plane shift is enhanced by the double application of the parallel offset (namely both on the first and on the second plane-parallel plates).

Regardless of the explained dispersion advantage, this embodiment of the invention also has the advantage of producing a desired total parallel offset or a desired total displacement of the interference pattern plane with thinner plane-parallel plates or with plane-parallel plates of a less refractive material, which is the case with a special choice of the used Radiation source can be helpful. In special cases in which the generation of a pattern with a uniform periodicity is not desired, but rather a change in the periodicity over the processing area composed of many individual lighting areas, in a further development of the invention it can be provided that at mirror-symmetrical positions in the beam paths of the diffraction rays Similar, mirror-symmetrically tiltable tilt axes aligned perpendicular to the diffraction plane and designed as prisms, additional beam modification elements are arranged. As explained in the introduction to the description, this type of targeted period adjustment is known from US Pat. No. 6904201 B1.

In order to carry out precise Z-tracking of the interference pattern or machining plane when machining a workpiece, precise knowledge of the surface shape and position of the workpiece is required in order to be able to control the tilting of the plane-parallel plates on this basis. Basically, the specific source of this surface data is irrelevant. However, the device according to the invention can itself be used to acquire such surface data.

The measurement method explained at the beginning is modified according to the invention in such a way that the variation of the vertical distance between the geometric intersection of the diffraction rays and the workpiece surface is no longer carried out by a slow vertical displacement of the workpiece, but by the vertical displacement of said intersection point by means of the tilting of the plane-parallel plates explained in detail above. In this way, the workpiece surface can be measured much faster than before. In particular, this makes it possible in an economically efficient way to have such a measurement interleaved in time with the workpiece processing: For each local processing area that is controlled by pivoting the input beam, a measurement step with an illumination fluence below the modification threshold of the workpiece material and then the the actual machining step is carried out with a fluence which at least partially exceeds the modification threshold of the workpiece material. Between these two steps, the processing plane is moved to the intended distance from the workpiece surface, in particular onto the workpiece surface. This is also done by precisely tilting the plane-parallel plates. It is also conceivable that input beams from different beam sources are used for the measurement on the one hand and the processing on the other. They would only have to be guided to the same entrance beam path by suitable beam guiding means, which is possible, for example, by means of semitransparent mirrors or other optical elements known to the person skilled in the art. This variant is particularly useful when the laser wavelength used for material processing cannot be detected by means of the selected image detector.

Brief description of the drawings

Show it:

Figure 1: a schematic representation of a first embodiment of a lighting device according to the invention,

FIG. 2: a schematic representation of a second embodiment of a lighting device according to the invention and

FIG. 3: a schematic representation of the section area of FIG

Diffraction rays to illustrate the surveying method according to the invention.

Description of preferred embodiments

Identical reference symbols in the figures indicate identical or analogous elements.

FIG. 1 shows in a highly schematic representation the essential parts of the beam path in a two-grating interferometer 10 according to the invention. The interferometer 10 has two diffraction gratings 11, 12, namely an input-side diffraction grating 11 and an output-side diffraction grating 12. The grating lines of the diffraction gratings 11, 12, which are oriented in the same way, are in a period ratio known to the person skilled in the art, as is described in general form in DE 102006032 053 A1. The input beam 20 hits the input side diffraction grating 11 on the input side. In the illustration of FIG Incidence of the input beam 20 on the diffraction grating 11 on the input side is shown. However, the input beam can also be deflected onto the input-side diffraction grating 11 at other angles of incidence by means of pivoting optics (not shown).

At the diffraction grating 11 on the input side, the input beam 20 is diffracted into partial beams of different diffraction orders. For reasons of simplification, only the symmetrical diffraction beams 21 of a single, selected diffraction order are shown in FIG. The partial beams of the other diffraction orders can, if they occur at all in a relevant manner, be blocked or deflected.

The diffraction beams 21 each strike first plane-parallel plates 31 arranged at mirror-symmetrical positions in a mirror-symmetrical alignment. The plane-parallel plates 31 are each shown in two positions. The respective basic position in which the first plane-parallel plates 31 are exactly perpendicular to the respectively assigned diffraction beam 21 is shown with dashed lines. In this basic position there is no change in the beam path, as indicated by the dotted continuation of the diffraction beams 21 behind the first plane-parallel plates 31.

The diffraction beams 21 then fall on the diffraction grating 12 on the output side and are again diffracted there in partial beams of different diffraction orders. A selected diffraction order, which depends on the period ratio of the diffraction gratings 11, 12, produces partial beams of the two diffraction beams 21 which intersect in an interference pattern plane 40, are superimposed there and form an interference pattern. If a machining plane of a workpiece lies in this interference pattern plane 40 and the fluence of the diffraction rays 21 is suitably selected, the material of the workpiece can be used in this machining or

Interference pattern plane 40 can be modified accordingly. Such a workpiece is not shown in FIG.

To shift the interference pattern plane, the first plane-parallel plates 31 can be aligned mirror-symmetrically around perpendicular to the diffraction plane spanned by the diffraction beams 21 (corresponding to the plane of the paper in FIG. 1) Tilt axes are tilted. The first plane-parallel plates 31 located in such a tilted position are shown in FIG. 1 with solid lines. In the positions shown in FIG. 1, the right one of the first plane-parallel plates 31 is tilted in the clockwise direction and the left one of the first plane-parallel plates is tilted counterclockwise.

This results in an oblique incidence of the diffraction rays 21 on the first plane-parallel plates 31, which results in a corresponding parallel offset of the diffraction rays 21. The beam path of the diffraction beams 21 with parallel offset is shown in Figure 1 as a solid arrow line.

The parallel offset of the diffraction beams 21 by the first plane-parallel plates 31, which in particular does not imply any change in the angle of the beam path, does not change anything in the previously described renewed diffraction of the diffraction beams 21 at the diffraction grating 12 on the output side Diffraction grating 12 impinge, shifted towards one another compared to the situation with the first plane-parallel plates 31 in the basic position. This results in the diffraction beams 21 meeting behind the exit-side diffraction grating 12 in another interference pattern plane 40, in particular closer to the exit-side diffraction grating 12, and forming the interference pattern there. By appropriately controlling the tilted position of the first plane-parallel plates 31, the Z position of the interference pattern plane 40 and thus the processing plane for a workpiece can be set precisely. In particular, the processing plane can track a curved surface of the workpiece or be guided along a curved, predetermined processing surface when the workpiece is scanned by pivoting the input beam 20 in the course of a large-area processing.

FIG. 2 shows, in a representation similar to FIG. 1, a further development of the lighting device according to the invention, in addition to the first plane-parallel plates 31 arranged between the diffraction gratings 11, 12, second plane-parallel plates 32 being arranged behind the diffraction grating 12 on the output side. The device of FIG. 2 is particularly suitable for cases in which the input beam 20 is a pulsed laser beam with a short pulse duration. As is known to the person skilled in the art, the necessary spectral bandwidth within a laser pulse is greater, the shorter its pulse duration. In the case of ultrashort pulses, the wavelength spectrum within the pulse is very broad. In the context of the present invention, this can be problematic insofar as the diffraction gratings 11, 12 have a significant angular dispersion, ie a dependence of the diffraction angle on the wavelength of the input beam. In the case of a broadband input beam, components of different wavelengths are thus diffracted at different angles, which is symbolized in FIG. 1 in a greatly exaggerated manner by the double representation of diffraction beams 21, 22 in each case. The diffraction beams 21, 22 are intended to represent the beam paths of the respectively shortest (diffraction beams 22) and respectively longest wavelengths (diffraction beams 21) within the input beam spectrum. In this example, the plane-parallel plates 31, 32 are set in such a way that the short-wave diffraction rays 22 impinge perpendicularly in their basic position.

This dispersion problem has no influence on the basic function of a two-grating interferometer, since in the absence of any plane-parallel plates 31, 32 the effects on the diffraction gratings 11, 12 completely compensate one another. However, this changes with the introduction of the first plane-parallel plates 31. The extent of the parallel offset achieved by them is namely dependent on the angle of incidence of the diffraction rays 21 on their surface. Since this, as explained above, is different for different wavelengths due to the angular dispersion of the diffraction grating 11 on the input side, there are wavelength-dependent parallel offsets behind the first plane-parallel plates 31, which in a device according to FIG. 1 would lead to wavelength-dependent Z-positions of the respective interference pattern. This "smears" the machining plane for a workpiece.

If, however, as shown in FIG. 2, additional, second plane-parallel plates 32 are arranged behind the diffraction grating on the output side, which correspond to the first plane-parallel plates 31 in terms of thickness and material, and, as shown in FIG Diffraction gratings 11, 12 are tilted, the dispersion effect can be largely (in a linear approximation completely) compensated. Those beam portions of the diffraction rays which hit the first plane-parallel plates 31 with a larger entrance angle (long-wave diffraction rays 21 in FIG. 2) hit the with a smaller angle of incidence second plane-parallel plates 32. These beam components thus experience a greater parallel offset on the first plane-parallel plates 31 and a smaller parallel offset on the second plane-parallel plates 32. In comparison to this, those beam components which strike the first plane-parallel plates 31 with a smaller angle of incidence (short-wave diffraction rays 22) experience a smaller parallel offset there and a larger parallel offset on the second plane-parallel plates 32, which they strike at a larger angle of incidence. As a result, all of the spectral beam components of the diffraction beams 21, 22 meet in the same interference pattern plane 40 and form a precisely defined, sharp interference pattern there. However, this approach neglects the effect of the dispersion caused by the plate material itself, which in most cases is entirely justifiable due to the small extent of the resulting error. Both dispersion effects can, however, be largely compensated for by using slightly different thicknesses (and / or slightly different materials with regard to their refractive index) for the first plane-parallel flaps 31 on the one hand and the second plane-parallel plates 32 on the other.

FIG. 3 shows, likewise in a highly schematic manner, the intersection area of the diffraction beams 21 when the two-grating interferometer 10 according to the invention is not shown in detail, in which the interference pattern plane 40, in which the geometric intersection 23 of the diffraction beams 21 lies, is around perpendicular distance 61 is arranged above a workpiece surface 50. The person skilled in the art will also be able to imagine the opposite situation in which the geometric intersection point 23 lies below the workpiece surface 50. In both cases, the diffraction beams 21 impinge on the workpiece surface 50 at points of incidence 24 laterally spaced from one another. Their lateral spacing 62 changes with the change in vertical spacing 61. According to the invention, this is varied by vertical displacement of geometric intersection point 23 by tilting plane-parallel plates 31, 32 (not shown in FIG. 3). The points of impact 24 are imaged on an image detector and their movement is analyzed as a function of the tilting of the plate.

Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative embodiments of the present invention Invention. In the light of the disclosure here, a person skilled in the art is provided with a broad spectrum of possible variations.

List of reference symbols

10 two-grating interferometer

11 diffraction grating on the input side of 10

12 diffraction grating on the output side of 10

20 input beam

21 diffraction rays

22 diffraction rays

23 geometric intersection

24 point of impact

31 first plane-parallel plates

32 second plane-parallel plates 40 interference pattern plane 50 workpiece surface 61 perpendicular distance 62 lateral distance

Claims

1. A device for illuminating a workpiece with an interference pattern, comprising a two-grating (11, 12) oriented perpendicular to its optical axis and arranged at a distance from each other, namely an input-side (11) and an output-side diffraction grating (12), having two-grating Interferometer (10) for generating diffraction beams (21, 22) that run along different beam paths in a common diffraction plane and interfere with one another in an interference pattern plane (40) by diffracting an input beam (21) at the input side (11) and refracting the resulting diffraction beams (21) , 22) on the diffraction grating (12) on the output side, wherein at mirror-symmetrical positions in the beam paths of the diffraction beams (21, 22) similar tilting axes that are synchronized and mirror-symmetrically tiltable are arranged around the diffraction plane, characterized in that the stra HL modification elements are designed as plane-parallel plates (31, 32).

2. Device according to claim 1, characterized in that two first (31) of the plane-parallel plates are arranged in the area between the diffraction gratings (11, 12).

3. Device according to claim 2, characterized in that two second (32) of the plane-parallel plates are additionally arranged in the area between the diffraction grating (12) on the output side and the interference pattern plane (40).

4. Device according to one of the preceding claims, characterized in that, at mirror-symmetrical positions in the beam paths of the diffraction beams, additional beam modification elements of the same kind, synchronized mirror-symmetrically tilting axes aligned perpendicular to the diffraction plane and designed as prisms, are arranged.

5. A method for modifying a workpiece by means of a two-grating interferometer (10) with an input-side (11) and an output-side diffraction grating (12), comprising the steps:

- Generating diffraction beams (21, 22) running along different beam paths in a common diffraction plane by bending a pulsed input beam (20) at the diffraction grating (11) and on the input side

- Generating an interference pattern in a processing plane of the workpiece by superimposing the diffraction beams (21, 22) by means of their renewed diffraction at the exit-side diffraction grating (12), the input beam (20) being pivoted in a manner synchronized with its pulse rate, around different areas of the processing plane to illuminate the interference pattern, and at mirror-symmetrical positions in the beam paths of the diffraction beams (21, 22) similar beam modification elements are tilted mirror-symmetrically about tilt axes aligned perpendicular to the diffraction plane in synchronized with the input beam pulses, characterized in that the beam modification elements as plane-parallel plates (31 , 32) are formed, by tilting a predetermined distance between the respectively illuminated area of the processing plane on the one hand and the workpiece surface on the other hand is set.

6. The method according to claim 5, characterized in that two first (31) of the plane-parallel plates are arranged in the area between the diffraction gratings (11, 12).

7. The method according to claim 6, characterized in that two second (32) of the plane-parallel plates are additionally arranged in the area between the diffraction grating (32) on the output side and the processing plane.

8. The method according to claim 7, characterized in that the second plane-parallel plates (32) are each tilted in the same direction as the first plane-parallel plates (31) by the same angular amount.

9. The method according to any one of claims 5 to 8, characterized in that at mirror-symmetrical positions in the radiation paths of the diffraction beams, similar, additional beam modification elements designed as primes are tilted mirror-symmetrically about tilt axes aligned perpendicular to the diffraction plane in a manner synchronized with the input beam pulses.

10. The method according to any one of claims 5 to 9, characterized in that the fluence of the interference pattern is set so that a material modification limit of the workpiece is exceeded in the areas of its illumination maxima and undershot in the areas of its illumination minima.

11. A method for measuring a workpiece surface by means of a two-grating interferometer (10) with an input-side (11) and an output-side diffraction grating (12), comprising the steps:

- Generation of diffraction beams (21, 22) that run along different beam paths in a common diffraction plane, first apart and then again towards a common geometric intersection point, by bending an input beam (20) at the entrance-side diffraction grating (11) and renewed diffraction of the resulting diffraction beams (21, 22) on the diffraction grating (12) on the outlet side, - Determining the perpendicular distance between the workpiece surface and the geometric intersection of the diffraction beams (21, 22), wherein the determination of said perpendicular distance comprises varying the same,

- Calculating a local surface height value from the determined vertical distance, the input beam (20) being swiveled over the workpiece surface in order to obtain the associated local surface height values for a plurality of points on the workpiece surface by repeating the aforementioned steps, characterized in that said varying of the vertical distance between the workpiece surface and the geometric intersection of the diffraction beams (21, 22) is carried out by plane-parallel plates (31, 32) arranged in mirror-symmetrical positions in the beam paths of the diffraction beams (21, 22), mirror-symmetrical and synchronized around perpendicular to the diffraction plane Tilt axes are tilted.

12. The method according to claim 11, characterized in that the calculated surface height values are used as part of a method according to one of claims 5 to 10 as a basis for controlling the tilting of the plane-parallel plates (31, 32).