Optical device, optical system, and use of the optical device to machine a sample by means of interfering laser beams

Abstract

The invention relates to an optical device for machining a sample by means of interfering laser beams. The optical device has at least one beam splitter, at least one interference lens associated with the beam splitter, and at least one beam-shaping lens. The beam splitter is arranged in such a way that a laser beam incident on the optical device can be split into at least two partial beams along an interference axis perpendicular to the optical axis. The interference lens is arranged downstream of the beam splitter in such a way that the partial beams can be deflected relative to one another in such a way that the partial beams interfere with one another in an interference region so that the sample can be machined in the interference region. The beam-shaping lens is arranged in such a way that the laser beam can be focused with respect to a focussing axis arranged perpendicularly to the interference axis and to the optical axis. The beam-shaping lens is arranged upstream of the interference lens. The invention also relates to an optical system and to the use of the optical device.

Description

[0001] Optical device, optical system and use of the optical device for processing a sample by means of interfering laser beams

[0002] The invention relates to an optical device, an optical system and the use of the optical device for processing a sample by means of interfering laser beams.

[0003] Optical devices are known from the prior art which have a beam splitter for splitting a laser beam directed onto the optical device into at least two partial beams, the two partial beams being deflected towards one another by a converging lens arranged downstream of the beam splitter in such a way that the partial beams interfere with one another in an interference region in order to process a sample arranged in the interference region. By processing the sample in this way using interfering laser beams, the sample can be processed at a high processing speed, in particular compared to processing the sample using a single laser beam. Essential to this process acceleration is the comparatively large processing area, which essentially corresponds to the interference region of the interfering partial beams.

[0004] The known optical devices have the disadvantage that in the case of a comparatively poor beam quality of the laser beam directed onto the optical device, a surface treatment of the sample is no longer guaranteed to the desired extent, since due to divergence effects and a reduced coherence length of the laser radiation caused by the poor beam quality, the

[0005] Size of the interference area is reduced.

[0006] It is therefore the object of the invention to eliminate the disadvantages of the prior art mentioned and in particular to develop an optical device which can be used with different beam geometries and profiles of the laser radiation incident on the optical device for the efficient processing of the sample.

[0007] The object of the invention is achieved by an optical device having the features of claim 1, an optical system having the features of claim 18 and a use of the optical device according to claim 19.

[0008] The optical device according to the invention has at least one beam splitter, at least one interference lens assigned to the beam splitter and at least one beam shaping lens, wherein the beam splitter is arranged such that a laser beam incident on the optical device can be split into at least two partial beams in an interference axis perpendicular to the optical axis, wherein the interference lens is arranged downstream of the beam splitter in such a way that the partial beams can be deflected towards one another in such a way that the partial beams interfere with one another in an interference region, so that the sample can be processed in the interference region, wherein the beam shaping lens is arranged such that the laser beam, in particular its partial beams, can be focused in a focusing axis arranged perpendicular to the interference axis and to the optical axis, wherein the beam shaping lens is arranged upstream of the interference lens.The optical system according to the invention comprises a laser source and the optical device, wherein the laser source is designed to emit a laser beam directed onto the optical device. The use according to the invention of the optical device, in particular of the optical system, comprises providing the sample in the interference region of the partial beams and processing it there by a laser beam passing through the optical device, in particular by its partial beams.

[0009] The invention is based on the fundamental idea that by focusing the laser beam, in particular its partial beams, due to the beam shaping lens in the focusing axis, the diameter of the laser radiation is reduced, in addition to focusing the partial beams in the interference axis. This brings about a greater spatial energy density in the interference region within which the sample is to be processed, which is also referred to as fluence. Ultimately, this serves to ensure that the sample can still be processed with a sufficiently high energy density, in particular ablatively and with interfering laser beams, even when using beam sources with a comparatively poor beam profile which, within the meaning of the invention, have a deviation from the ideal Gaussian profile that is relevant for reworking the sample.At the same time, the inventive arrangement of the beam shaping lens upstream of the interference lens does not increase the axial length of the optical device along the optical axis, so that the greatest possible working distance is still provided, which essentially corresponds to the distance between the last optical component of the optical device, seen downstream of the beam, and the interference region. This serves to ensure that the sample can still be processed at the greatest possible distance from the optical device. The optical device according to the invention is therefore particularly suitable for use in combination with a fiber laser which is designed to emit the laser radiation incident on the optical device.A further fundamental consideration of the invention is that the use of laser radiation with a comparatively poor beam profile results in poor focusability of the laser beams over long distances along the optical axis. Therefore, the arrangement of the beam-shaping lens downstream of the interference lens makes it possible to effectively process the sample even with laser beams with a poor beam profile. In particular, improved resolution during sample processing is enabled.

[0010] Preferably, the interference lens and / or the beam-shaping lens are each designed as converging lenses. The at least one beam splitter can be designed as a diffractive optical element, in particular as a grating, in order to split the laser beam impinging on the beam splitter into the at least two partial beams with the aid of diffraction effects. The beam-shaping lens is preferably arranged downstream of the beam splitter in order to achieve a compact design of the optical device.

[0011] Preferably, the beam splitter for splitting the laser beam is designed only along the interference axis, and the interference lens for deflecting the partial beams is designed only along the interference axis, in order to be able to design the geometry of the interference region as advantageously as possible. Alternatively or additionally, the beam-shaping lens for focusing the laser beam or its partial beams can be designed only along the focusing axis, in order to also influence the geometry of the interference region perpendicular to the interference axis.If the division of the laser beam and the deflection of the partial beams are only designed in the interference axis and the focusing of the laser beam or its partial beams by the beam shaping lens is only designed in the focusing axis, a spatial-functional division of the beam shaping of the laser beam becomes possible, which is also referred to as beam shaping, namely in that the influencing of the partial beams with one another can be carried out by optical components with an effect only in the interference axis, whereas the influencing of the focusing of the laser beam or its partial beams can take place by optical components with an effect only in the focusing axis. For the purposes of the invention, the interference axis can be defined by the division of the partial beams, while the focusing axis is arranged perpendicular to the interference axis.Undesirable interactions between these two functional components can thus be avoided.

[0012] In a further embodiment of the invention, the beam splitter can be designed to split the laser beam into at least three, four or five partial beams. The beam splitter can be designed to split the laser beam into the partial beams along at least two axes, each of which is aligned perpendicular to the optical axis, in particular along the interference axis and the focusing axis. In an advantageous embodiment of the invention, the interference lens and / or the beam shaping lens can each be designed as a cylindrical lens. The beam shaping lens is preferably arranged as a cylindrical lens perpendicular to the interference lens as a cylindrical lens. For the purposes of the invention, a cylindrical lens has a refractive effect on the laser radiation incident on the cylindrical lens only in one axis, while in an axis perpendicular to this there is no appreciable influence on the laser radiation.According to the invention, laser radiation incident on a cylindrical lens is refracted only in one axis.

[0013] The focal point of the beam shaping lens can be arranged at the same height along the optical axis as the interference region assigned to the interference lens in order to provide the greatest possible spatial energy density of the laser radiation for processing the sample in both the interference axis and the focusing axis.

[0014] The interference lens is preferably a component of an imaging system assigned to the beam splitter, which is designed in particular to image the partial beams emerging from the beam splitter onto the interference region. The imaging system can have one or more additional lenses to the interference lens in order to improve the beam quality of the partial beams passing through the imaging system. The imaging system can be arranged downstream of the beam splitter in order to obtain a compact structure. A further advantage of using the imaging system is the extensive preservation of the phase fronts of the laser beam passing through the imaging system, in particular of its partial beams, even in the case of laser beams with low temporal coherence.

[0015] The imaging system is preferably designed as a 4 f-image system and in particular has a further interference lens assigned to the interference lens, which is designed in particular as a cylindrical lens aligned parallel to the interference lens and arranged upstream of the latter. The interference lens is preferably designed as a converging lens. The optical imaging system can be arranged axially between the beam splitter and the interference region. Furthermore, a further interference lens assigned to the interference lens can be formed, even without forming an imaging system. In an advantageous development of the invention, the interference lens facing the beam splitter is arranged at a distance from the beam splitter which corresponds to the focal length of this interference lens. The distance between two interference lenses can correspond to the sum of their focal lengths.The interference lens facing the interference region is arranged at a distance from the interference region that corresponds to the focal length of this interference lens. The interference lenses of the imaging system can be designed as cylindrical lenses. The further interference lens can be designed as a converging lens. The use of a 4 f imaging system results in the advantage of adjustable magnification of the partial beams emerging from the imaging system, particularly with regard to their cross-section. In addition, a 4 f imaging system enables the use of lenses with a comparatively small lens cross-section, resulting in a compact design. A further advantage of a 4 f imaging system is its applicability with comparatively low temporal and / or spatial coherence of the partial beams passing through the imaging system, which results in a spatially large interference region.In this respect, even with the low temporal and spatial coherence of the laser radiation of a fiber laser, a large processing area for the sample is still possible.

[0016] The imaging system can be designed as a 2 f-imaging system and, in particular, comprise only a single converging lens, in particular a cylindrical lens. In this respect, the interference lens of the 2 f-imaging system can be spaced from the beam splitter and / or the interference region at a distance corresponding to the focal length of the interference lens.

[0017] The beam-shaping lens is preferably arranged between the interference lenses, in particular between the interference lenses of the imaging system. The beam-shaping lens can be arranged upstream and adjacent, in particular directly adjacent, to the interference lens of the imaging system facing the interference region. This enables a compact design of the optical device and its use in conjunction with comparatively poor beam quality of the laser radiation.

[0018] Preferably, an optical beam expander is arranged upstream of the beam shaping lens, which optical beam expander is designed such that the diameter of a laser beam impinging on the beam expander is increased. In this respect, the beam expander is also referred to as a "beam expander". The optical device can be designed such that the laser beam impinging on the optical beam expander and / or emerging from the optical beam expander is each aligned coaxially. By using the optical beam expander and the resulting increase in the diameter of the laser beam, its spatial energy density or fluence is reduced at least in some regions within the optical device.Particularly when using a 4f imaging system, this largely prevents the energy density of the laser radiation within the optical device from being so high that air breakthrough occurs due to non-linear absorption effects, thereby impairing the processing of the sample. A further advantage of using the optical beam expander is that the cross-sectional area of ​​the laser beam incident on the beam shaping lens is increased, so that a larger lens area can be used to focus the laser beam and a greater focusing effect of the beam shaping lens is achieved, which ultimately improves the processing of the sample. The optical device can be designed to expand and / or focus the laser beam in the optical device, particularly in the focusing axis.

[0019] The beam expansion means can have a diverging lens and a converging lens arranged downstream of the beam, wherein the diverging lens and / or the converging lens can be designed as cylindrical lenses. In particular when the beam expansion means is assigned to the beam shaping lens, the diverging lens and / or the converging lens can each be aligned as cylindrical lenses parallel to one another and in particular parallel to the beam shaping lens, so that the increase in the diameter of the laser beam caused by the beam expansion means only occurs in the focusing axis. In an advantageous further development of the invention, the beam expansion means can axially surround the beam splitter in order to obtain a compact structure. In particular, it can be provided that the diverging lens is arranged upstream of the beam splitter and / or the converging lens is arranged downstream of the beam splitter.In a further embodiment of the invention, the converging lens is arranged upstream of the beam splitter and / or the diverging lens is arranged downstream of the beam splitter. In a further embodiment, the beam expanding means can be arranged upstream of the beam splitter.

[0020] Preferably, the beam expander is configured to increase the diameter of the laser beam passing through it only along the focusing axis in order to avoid undesirable interaction with the optical components of the optical device associated with the interference axis. To achieve a compact design, the beam expander can axially surround, at least in part, the optical imaging system associated with the beam splitter.

[0021] Preferably, a beam compression means is arranged upstream of the interference lens, which beam compression means is designed such that the diameter of a laser beam impinging on the beam compression means is reduced, wherein the reduction occurs in particular only in the interference axis. Preferably, the beam compression means has a converging lens and a diverging lens arranged downstream of the converging lens. According to an alternative embodiment, the beam compression means can have a diverging lens and a converging lens arranged downstream of the diverging lens. Preferably, the converging lens and the diverging lens are each designed as cylindrical lenses, in particular aligned parallel to one another, wherein the cylindrical lenses are aligned as a cylindrical lens, in particular parallel to the interference lens.The optical effect of the beam compression means thus extends only to the interference axis and not to the focusing axis. The beam compression means can be arranged upstream of the beam splitter in order to keep the interference angle of the partial beams stable and, moreover, to obtain a greater energy density in the interference region. To achieve a compact design of the optical device, the beam compression means can be surrounded at least in regions, in particular completely, by the beam expansion means. Further embodiments of the invention can provide that the beam expansion means and / or the beam compression means are arranged upstream of the beam splitter. Furthermore, it can be provided that the beam expansion means is arranged upstream of the beam compression means. In an alternative embodiment, this can be configured the other way around.

[0022] The optical system according to the invention for processing a sample by means of interfering laser radiation comprises a laser and an optical device according to the invention, wherein the laser is designed to emit a laser beam directed towards the optical device arranged downstream of the laser. The laser can be a fiber laser. The laser radiation emitted by the laser can be multimodal and in particular can have several transverse modes. The laser beam of the laser directed towards the optical device can have a M 2-parameters in the range between 1 and 40, in particular between 1 and 20. The laser beam can have a wavelength between 266 nm and 1064 nm, in particular a wavelength of 1064 nm, 532 nm, 355 nm or 266 nm. To influence the laser beam, for example to improve its focusability and / or to generate the desired wavelength, the optical system can have at least one non-linear optical component with an optically non-linear medium. The laser beam of the laser source can be in the form of permanent, i.e. non-pulsed, laser radiation, which is also referred to as cw laser radiation ("continuous wave"). Alternatively, the laser beam may be pulsed and preferably have a pulse duration between 100 fs and 500 ns, in particular between 100 fs and 300 ns, most preferably between 100 fs and 100 ns.The cross-section of the laser beam can be circular, elliptical, or approximately quadrangular, in particular rectangular. To influence the cross-section of the laser beam, the optical system can comprise a beam-shaping means. The cross-section of the laser beam can have a diameter of between 10 mm and 20 mm, in particular approximately 15 mm, at least in some regions along the optical axis.

[0023] To compensate for optical errors, one or more of the lenses mentioned can each be designed as a lens system. The components of the optical device acting on the focusing axis can be arranged axially separate from the components of the optical device acting on the interference axis. The components of the optical device acting on the focusing axis can be arranged upstream of the components of the optical device acting on the interference axis.

[0024] The optical components of the optical device, in particular the beam splitter, the beam expanding means, the beam compressing means, the optical imaging system, the interference lens and / or the beam shaping lens can be designed to be movable along the optical axis.

[0025] Further advantages and features emerge from the claims and from the following description, in which exemplary embodiments of the invention are explained in detail with reference to the drawings. In the drawings:

[0026] Fig. 1 shows an optical device according to the invention in a side view,

[0027] Fig. 2 shows the optical device according to Fig. 1 in a plan view,

[0028] Fig. 3 shows a further embodiment of the optical device according to the invention in a side view,

[0029] Fig. 4 shows the optical device according to Fig. 3 in a plan view,

[0030] Fig. 5 shows a further embodiment of the optical device according to the invention in a side view and

[0031] Fig. 6 shows the optical device according to Fig. 5 in a plan view. Fig. 1 shows schematically an optical system 1 according to the invention in a side view with a laser source 2 arranged on the left-hand side, which laser source 2 is designed as a fiber laser 2 in the exemplary embodiment shown and emits a laser beam 4 directed to the right onto an optical device 3 according to the invention of the optical system 1. According to Fig. 1, the laser beam 4 of the laser source 2 is directed parallel to the optical axis, which corresponds to the z-axis in the sense of a three-dimensional Cartesian coordinate system. A direction downstream of the beam therefore points to the right in Fig. 1, whereas an upstream direction points to the left. The x- and y-directions are perpendicular to one another and each perpendicular to the optical axis. As shown in Fig.As indicated in Fig. 1, the xz-plane of the optical system 1 is shown, the x-axis corresponding to the focusing axis in the sense of the invention, while Fig. 2 shows the optical system 1 in the yz-plane, the y-axis corresponding to the interference axis in the sense of the invention.

[0032] The laser beam 4 has a wavelength of 1064 nm and a diameter of approximately 15 mm, wherein the beam profile of the laser beam 4 is approximately circular upon impingement on the optical device 3. The laser beam 4 has a M 2-value of approximately 40 as well as several transverse modes, which are usually denoted by TMXY, where X denotes the mode in the X direction and Y the mode in the Y direction. The beam shape of the laser radiation 4 emitted by the fiber laser 2 therefore deviates significantly from the usual beam shape of a solid-state laser, which essentially corresponds to a classic Gaussian profile. The beam shape therefore has poorer divergence properties as well as a reduced coherence length.

[0033] The laser beam 4 directed towards the optical device 3 strikes it as collimated laser radiation. The laser beam 4 first strikes a beam expander 5 of the optical device 3, which is also referred to as a beam expander and increases the diameter of the laser beam 4 passing through the beam expander 5, but only in the focusing axis, as is illustrated by the xz plane shown in Fig. 1. For this purpose, a first lens 6 of the beam expander 5 is designed as a biconcave cylindrical lens 6 and is aligned such that the refractive effect on the laser beam 4 occurs only in the focusing axis. The divergent laser beam 4 emerging after the cylindrical lens 6 strikes a biconvex cylindrical lens 7 downstream of the beam as a further lens of the beam expander 5, which is aligned parallel to the converging lens 6. The cylindrical lens 7 therefore focuses the laser beam 4 only in the focusing axis.The focal lengths and the spacing of the two cylindrical lenses 6, 7 of the beam expander 5 are coordinated with one another in such a way that the laser beam 4 emerging from the cylindrical lens 7 is essentially collimated, i.e., aligned parallel to the optical axis. As can be seen from the yz plane shown in Fig. 2, the beam expander 5 does not cause any significant expansion of the laser beam 4 in the interference axis arranged perpendicular to the focusing axis.

[0034] The coaxially aligned laser beam 4 emerging from the beam expander 5 strikes a beam shaping lens 8 downstream of the beam, which is aligned as a biconvex cylindrical lens 8 parallel to the cylindrical lenses 6, 7 of the beam expander 5, so that the focusing effect of the beam shaping lens 8 on the laser beam 4 occurs only in the focusing axis. The focal length of the beam shaping lens 8 is selected such that the focal point 9 of the laser radiation 4 in the focusing axis coincides with the interference region 19 described below with regard to the interference axis. As a result, a sample 10 arranged in the focal point 9 of the beam shaping lens 8 can be processed by means of interfering laser beams 15, 16, wherein the beam shaping lens 8 additionally has a focusing effect on the laser radiation in the focusing axis.The beam expanding means 5 ensures that the largest possible lens surface of the beam forming lens 8 after the beam expanding means 5 can be used to focus the laser beam 4 in the focusing axis in order to obtain the largest possible interference area 19 despite the comparatively poor beam profile.

[0035] Fig. 2 shows the optical system 1 according to Fig. 1 in the yz plane, which illustrates the beam path in the interference axis aligned perpendicular to the focusing axis. The laser beam 4 incident on the optical device 3 passes through the two cylindrical lenses 6, 7 of the beam expander 5, as already mentioned, wherein, due to their alignment, no appreciable influence occurs on the laser beam 4 in the interference axis. Similarly, the beam shaping lens 8 also has no effect on the laser beam 4 in the interference axis. After the beam shaping lens 8, the laser beam 4 strikes an optical beam compression means 11, which comprises a biconvex lens 12 facing the laser source 3 and a biconcave lens 13 facing away from the laser source 3. These two lenses 12, 13 are each designed as cylindrical lenses 12, 13 aligned parallel to each other and perpendicular to the beam forming lens 8.As a result, the cylindrical lens 12 only focuses the laser beam 4 along the interference axis, and after the diverging lens 13, the laser beam 4 is again aligned coaxially with respect to the interference axis. After the beam compression means 11, the diameter of the laser beam 4 is reduced with respect to the interference axis, which increases the spatial energy density of the laser beam 4, which is also referred to as fluence. The focal lengths and the spacing of the cylindrical lenses 12, 13 of the beam compression means 11 are selected such that the laser beam 4 emerging from the beam compression means 11 is again aligned parallel to the optical axis with respect to the interference axis and does not exhibit any appreciable divergence.

[0036] The laser beam 4 then strikes a beam splitter 14, which in the present embodiment is designed as a diffractive optical element, for example as a grating. As a result, the laser beam 4 striking the beam splitter 14 is split only in the interference axis into two partial beams 15, 16, which each leave the beam splitter 14 at an angle of approximately 8° to the optical axis, but each exhibits no appreciable divergence. It can be seen from Fig. 1 that the beam splitter 14 does not split the laser beam 4 with respect to the xz plane, and therefore in the focusing axis. The two partial beams 15, 16 impinge downstream of the beam splitter 14 on a focusing biconvex cylindrical lens 17 which is assigned to the beam splitter 14 and is aligned parallel to the cylindrical lenses 12, 13 of the beam compression means 11, so that the optical effect of the cylindrical lens 17 occurs only in the interference axis.The cylindrical lens 17 deflects the partial beams 15, 16 towards one another in such a way that they interfere with one another in an interference region 19, the sample 10 arranged in the interference region 19 being ablatively processed by means of the interfering laser beams 15, 16. In this respect, the cylindrical lens 17 is also referred to as an interference lens 17 in the sense of the invention. The beam splitter 14 and the interference region 19 are each arranged at a distance from the interference lens 17 which corresponds to its focal length. In the present exemplary embodiment, the interference lens 17, due to its focal length and distance from the beam splitter 14, corresponds to an optical 2 f imaging system 18 which images the partial beams 15, 16 emerging from the beam splitter 14 back onto the axial height of the interference region 19.

[0037] From the beam path in the yz-plane shown in Fig. 2 it can be seen that the two partial beams 15, 16, after passing through the converging lens 17 on the way to the interference region 19, each have a minimally small lateral extent only in the interference axis, which is therefore also referred to as the beam waist 20. After the beam waist 20, the diameter of the partial beams 15, 16 widens again. In this respect, the energy density of the partial beams 15, 16 is comparatively large at the axial height of the beam waist 20. However, since the partial beams 15, 16 are in the xz-plane according to Fig. 1 are not significantly focused and still have sufficiently large diameters, the risk of optical breakthroughs, in particular due to non-linear absorption effects, at the axial height of the beam waist 20 and a resulting impairment during processing of the sample 10 is largely avoided.

[0038] Fig. 3 shows a further embodiment of the optical system 1 according to the invention with the already mentioned fiber laser 2 and the optical device 3 in the xz plane. Similar to the embodiment of Figs. 1 and 2, the fiber laser 2 emits a laser beam 4 aligned parallel to the optical axis onto the optical device 3. In the xz plane shown in Fig. 3, the laser beam 4 first strikes the optical beam expander 5 with the diverging lens 6 and the converging lens 7, both of which are designed as cylindrical lenses 6, 7 aligned parallel to one another. The laser beam 4 emerging from the beam expander 5 is coaxial, i.e. aligned parallel to the optical axis, and has no appreciable divergence. In this way, the laser beam 4 strikes the already mentioned beam forming lens 8, which focuses the laser beam 4 only in the focusing axis onto the focal point 9, which is as shown in Fig.1 and 2 coincides with the axial position of the interference region 19 .

[0039] In the yz-plane shown in Fig. 4, after emerging from the laser source 2, the laser beam 4 passes through the optical beam expander 5 and the beam shaping lens 8 designed as a cylindrical lens without any appreciable influence. Downstream of the beam shaping lens 8, the laser beam 4 passes through the beam compression means 11, which is designed essentially analogously to the design according to Fig. 2 and reduces the diameter of the laser beam only in the interference axis. After the beam compression means 11, the laser beam 4 strikes the beam splitter 14, which is again designed as a diffractive optical element, so that the laser beam 14 is split in the interference axis into two partial beams 15, 16, which are aligned along the optical axis, but each at an angle of approximately 8° thereto and each have no appreciable divergence.Downstream of the beam splitter 14, the partial beams 15, 16 impinge on an optical imaging system 18, which in the present embodiment is designed as a 4 f imaging system, by which the partial beams 15, 16 are ultimately deflected toward one another and in the direction of the interference region 19. The 4 f imaging system 18 has a first biconvex converging lens, facing the beam splitter 14, as the first interference lens 21, and a second biconvex converging lens, facing the interference region 19, as the second interference lens 22. Both interference lenses 21, 22 are designed as cylindrical lenses 21, 22 aligned parallel to one another, so that there is no significant influence on the laser beam 4 or its partial beams 15, 16 in the focusing axis, as illustrated in Fig. 3.The focal lengths and the spacings of the interference lenses 21, 22 of the 4 f imaging system 18 are selected such that the first interference lens 21 is arranged at a distance from the beam splitter 14 that corresponds to its focal length. Correspondingly, the second interference lens 22 facing the interference region 19 is arranged at a distance from the interference region 19 that corresponds to its focal length. The interference lenses 21, 22 are arranged at a distance from one another that corresponds to the sum of the two focal lengths. As can be seen from the beam path shown in Fig. 4, the two partial beams 15, 16 between the two interference lenses 21, 22 of the 4 f imaging system 18 each have a minimum beam diameter, hence a beam waist 20, after which they each widen again. Since at this axial height the partial beams 15 , 16 are arranged in the direction shown in Fig .3 still have a sufficiently large beam diameter, the risk of air breakthroughs is also reduced here.

[0040] After passing through the second interference lens 22, the two partial beams 15, 16 are deflected relative to one another in such a way that they interfere with one another in the interference region 19, as already described in connection with Figs. 1 and 2, in order to interferometrically ablatively process the sample 10 arranged in the interference region 19. The partial beams 15, 16 emerging from the second interference lens 22 each exhibit no appreciable divergence in order to create a large-area interference region 19.

[0041] Fig. 5 shows a further embodiment of the optical device 3, which together with the fiber laser 2 already described forms the optical system 1, in the xz plane.

[0042] The laser beam 4 emitted by the fiber laser 2 initially strikes the first cylindrical lens 6 of the beam expander 5, which is designed as a plano-concave cylindrical lens 6 whose scattering effect on the laser beam 4 occurs only in the focusing axis. The laser beam 4 leaves the cylindrical lens 6 divergently only in the focusing axis and strikes a second cylindrical lens 7 of the beam expander 5, which is arranged downstream of the cylindrical lens 6 and is designed as a plano-convex cylindrical lens 7 aligned parallel to the cylindrical lens 6. The distance between the two cylindrical lenses 6, 7 and their focal lengths are selected such that the laser beam 4 emerging from the cylindrical lens 7 is aligned coaxially.In this form, the laser beam 4 reaches the already described beam forming lens 8, which is here biconvex and aligned parallel to the cylindrical lenses 6, 7 of the beam expanding means 5, as a cylindrical lens 8, which focuses the laser beam 4 only in the focusing axis onto the interference area 9 in order to process the sample 10 arranged there.

[0043] Fig. 6 shows the optical system 1 in the yz plane. The laser beam 4 emerging from the fiber laser 2 passes through the cylindrical lens 6 without any relevant effect in the interference axis and then strikes a plano-convex cylindrical lens 12 arranged downstream of the cylindrical lens 6, which is aligned perpendicular to the cylindrical lens 6 so that its effect only occurs in the interference axis. The cylindrical lens 12 is the first lens 12 of the beam compression means 11. The laser beam 4 converging after the cylindrical lens 12 strikes the second lens 13 of the beam compression means 11, which is arranged downstream of the cylindrical lens 12 and is designed as a cylindrical lens 13 aligned parallel to the lens 12. The distance between the cylindrical lenses 12 , 13 of the beam compression means 11 and their focal lengths are selected such that the laser beam 4 leaves this as a coaxial laser beam 4 .Downstream of the beam compression means 11, the laser beam 4 reaches the beam splitter 14 and is split into two partial beams 15, 16 in the interference axis, as already described. The partial beams 15, 16 first pass through the first interference lens 21, designed here as a biconvex cylindrical lens 21, of the optical imaging system 18, which here, similar to the embodiment in Fig. 4, is designed as a 4 f imaging system. The first interference lens 21 refracts both partial beams 15, 16 along the optical axis in such a way that they each initially converge and then, after formation of the beam waist 20, diverge, reach the second interference lens 22. The second interference lens.

[0044] 22 is designed as a biconvex cylindrical lens 22 aligned parallel to the first interference lens 21 and deflects both partial beams 15, 16 in such a way that they interfere with each other in the interference region 19, each without any significant divergence but at a finite angle to the optical axis, and thus process the sample 10. The interference region 19 in the interference axis and the focal point 9 in the focusing axis are at the same height along the optical axis. From the representations in Fig.

[0045] 5 and 6 show that the beam compression means 11 is arranged upstream of the beam splitter 14. The beam compression means 11 and the beam splitter 14 are surrounded by the beam expansion means 5, and the imaging system 18 at least partially surrounds the beam expansion means 5.

Claims

Patent claims 1. Optical device (3) for processing a sample (10) by means of interfering laser beams (15, 16), with at least one beam splitter (14), with at least one interference lens (17, 22) associated with the beam splitter (14) and with at least one beam shaping lens (8), wherein the beam splitter (14) is arranged such that a laser beam (4) impinging on the optical device (3) can be split into at least two partial beams (15, 16) in an interference axis perpendicular to the optical axis, wherein the interference lens (17, 22) is arranged downstream of the beam splitter (14) such that the partial beams (15, 16) can be deflected relative to one another such that the partial beams (15, 16) interfere with one another in an interference region (19), so that the sample (10) in the interference region (19) can be processed, wherein the beam shaping lens (8) is arranged such that the laser beam (4), in particular its partial beams (15, 16),can be focused in a focusing axis arranged perpendicular to the interference axis and the optical axis, wherein the beam-shaping lens (8) is arranged upstream of the interference lens (17, 22).

2. Optical device (3) according to claim 1, characterized in that the beam shaping lens (8) is arranged downstream of the beam splitter (14).

3. Optical device (3) according to one of claims 1 or 2, characterized in that the beam splitter (14) for splitting the laser beam (4) only in the in- interference axis and the interference lens (17, 22) to Deflection of the partial beams (15, 16) is only formed in the interference axis and / or that the beam shaping lens (8) for focusing the laser beam (4) or its partial beams (15, 16) is only formed in the focusing axis.

4. Optical device (3) according to one of the preceding claims, characterized in that the interference lens (17, 22) and / or the beam-shaping lens (8) are each designed as cylindrical lenses. In particular, it is provided that the beam-shaping lens (8) is oriented as a cylindrical lens perpendicular to the interference lens (17, 22) as a cylindrical lens.

5. Optical device (3) according to one of the preceding claims, characterized in that the focal point (9) the beam-shaping lens (8) is arranged at the same height along the optical axis as the interference region (19) associated with the interference lens (17, 22) 6. Optical device (3) according to one of the preceding claims, characterized in that the interference lens (17, 22) is a component of an optical imaging system (18) associated with the beam splitter (14).

7. Optical device (3) according to claim 6, characterized in that the imaging system (18) is designed as a 4f imaging system and in particular has a further interference lens (21) associated with the interference lens (22), which is in particular designed as a parallel cylindrical lens (21) aligned with the interference lens (22) and arranged upstream of the latter.

8. Optical device (3) according to one of claims 6 or 7, characterized in that the beam-shaping lens (8) is arranged between the interference lenses (21, 22) of the imaging system (18), in particular that the beam-shaping lens (8) is arranged upstream of the beam and adjacent, in particular directly adjacent, to the interference lens (22) of the imaging system (18) facing the interference region (19).

9. Optical device (3) according to one of the preceding claims, characterized in that an optical beam expanding means (5) is arranged, in particular upstream of the beam shaping lens (8), which is designed such that the diameter of a laser beam (4) impinging on the beam expanding means (5) is increased, in particular only in the focusing axis.

10. Optical device (3) according to claim 9, characterized in that the beam expanding means (5) has a diverging lens (6) and a converging lens (7) arranged downstream of the diverging lens (6), wherein the diverging lens (6) and / or the converging lens (7) are designed as cylindrical lenses.

11. Optical device (3) according to one of claims 9 or 10, characterized in that the beam expanding means (5) surrounds the beam splitter (14), wherein in particular the diverging lens (6) is arranged upstream of the beam of the beam splitter (14) and / or the converging lens (7) are arranged downstream of the beam splitter (14).

12. Optical device (3) according to one of claims 9 to 11, characterized in that the beam expanding means (5) axially surrounds at least partially the imaging system (18) associated with the beam splitter (14).

13. Optical device (3) according to one of the preceding claims, characterized in that a beam compression means (11) is arranged upstream of the interference lens (17, 22), which is designed such that the diameter of the laser beam (4) impinging on the beam compression means (11) is reduced, wherein the reduction takes place in particular only in the interference axis.

14. Optical device (3) according to claim 13, characterized in that the beam compression means (11) comprises a converging lens (12) and a diverging lens (13) arranged downstream of the converging lens (12).

15. Optical device (3) according to claim 14, characterized in that the converging lens (12) and the diverging lens (13) are designed as cylindrical lenses which are aligned in particular parallel to one another and which are aligned in particular parallel to the interference lens (17, 22) as a cylindrical lens.

16. Optical device (3) according to one of claims 13 to 15, characterized in that the beam compressor sion means (11) is arranged upstream of the beam splitter (14).

17. Optical device (3) according to one of claims 13 to 16, characterized in that the beam compression means (11) is at least partially, in particular completely, surrounded by the beam expansion means (5).

18. Optical system (3) for processing a sample (10) by means of interfering laser beams (15, 16), with a laser source (2) and an optical device (3) according to one of claims 1 to 17, wherein the laser source (2) is designed to emit a laser beam (4) directed onto the optical device (3).

19. Use of an optical device (3) according to one of claims 1 to 17, in particular of an optical system (1) according to claim 18, for processing a sample (10) by means of interfering laser beams (15, 16), wherein the sample (10) is provided in the interference region (19) of the partial beams (15, 16) and is processed there by a laser beam (4) passing through the optical device (3), in particular by its partial beams (15, 16).

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