Spatial frequency filter device for use with a laser beam, spatial frequency filter arrangement having such a spatial frequency filter device, and method for spatial frequency filtering of a laser beam

Abstract

The invention relates to a spatial frequency filter device (100) for use with a laser beam (200), the spatial frequency filter device having a neutral region (110) which is arranged to transmit or reflect the laser beam (200) and a deflection region (120) which is radially adjacent to the neutral region (110) and is arranged to deflect a beam component (210) of the laser beam (200) from a beam axis (A) of the laser beam (200), wherein the deflection region (120) The deflection region (120) has a constant portion (123), in which, for each position in the constant portion (123), the deflection effect on the beam component (210) of the laser beam (200) is independent of the distance of the position from the neutral region (110), and wherein the deflection region (120) has a variable portion (125), in which the deflection effect on the beam component (210) of the laser beam (200) varies depending on the distance from the neutral region (110).

Description

Technical Field

[0001] The invention relates to a spatial frequency filter device for use with a laser beam, a spatial frequency filter arrangement for a laser beam and a method for spatial frequency filtering a laser beam. Background Art

[0002] German published patent application DE 10 2004 058 044 A1 discloses a spatial frequency filter device for spatial frequency filtering of a laser beam, which has a transmission body which is at least partially transparent to the laser radiation, and an element which has a hole and is arranged adjacent to the transmission body or integrated in the transmission body, and which has a diffractive and / or refractive deflection structure. With the help of such a diffraction stop, undesired light components of the laser beam are purposefully diffracted to a well-defined solid angle, where they can be efficiently absorbed. For example, such a diffraction stop or aperture stop can provide a limitation of the beam leaving the transmission fiber at the outlet of the transmission fiber for the laser radiation and protect the rear components. The diffractive area of ​​such an stop avoids the interaction of the fringe field with the corresponding stop geometry, in particular with the interaction with the edge area of ​​the stop which is not optimal for production reasons and can affect the propagation properties of the useful beam. In the case of an aperture stop without a diffractive area, a virtual light source with an undesirable propagation direction can occur, which has a negative impact on the rear optical device or the workpiece to be processed.

[0003] Although this can be avoided by means of a diffraction stop, such as is known from DE 10 2004 058 044 A1, it is difficult or even impossible to use it to filter out unwanted beam components that overlap the main beam or useful beam. This becomes more difficult the more these unwanted beam components overlap the actual useful beam or main beam. Summary of the invention

[0004] The object of the present invention is to provide a spatial frequency filter device, a spatial frequency filter arrangement and a method for spatial frequency filtering of a laser beam in which the above-mentioned disadvantages do not occur.

[0005] This object is achieved by providing the technical teaching of the present invention, in particular the technical teaching of the independent claim and the technical teaching of the dependent claims and the embodiments disclosed in the specification.

[0006] This object is achieved in particular by providing a spatial frequency filter device for use with a laser beam, the spatial frequency filter device having a neutral region, which is arranged to transmit or reflect the laser beam. The spatial frequency filter device has a deflection region radially adjacent to the neutral region, which is arranged to deflect a beam component of the laser beam from the beam axis of the laser beam. The deflection region has a constant portion, in which, for each position in the constant portion, the deflection effect on the beam component of the laser beam is independent of the distance of the position from the neutral region. The deflection region also has a variation portion, in which the deflection effect on the beam component of the laser beam varies as a function of the distance from the neutral region. With the help of the constant portion of the deflection region, undesired beam components that are sufficiently separated from the main beam or useful beam can be reliably and effectively deflected and thus filtered. On the other hand, the varying portion of the deflection region allows an in particular gradual filtering of undesired beam components which are arranged very close to the main beam or the useful beam or overlap therewith, without the main beam or the useful beam being adversely influenced or excessively attenuated. The spatial frequency filter arrangement proposed here thus offers an improved possibility for filtering the laser beam, in particular also for removing undesired beam components which overlap the main beam or the useful beam.

[0007] The neutral region is in particular the region of the spatial frequency filter device in which the laser beam is transmitted or reflected without interference, ie in particular beam components of the laser beam are not deflected from the beam axis. The neutral region is therefore in particular provided for undisturbed transmission or reflection of the laser beam.

[0008] The radial direction is to be understood here as a direction perpendicular to the beam axis. The beam axis is in particular the propagation axis of the laser beam. Accordingly, it refers in particular to the propagation direction of the laser beam or extends in the propagation direction of the laser beam. The beam axis is in particular the axis that coincides with the Poynting vector of the laser beam.

[0009] The effect that varies in the varying portion means in particular that the deflection efficiency, in particular the strength of the phase modulation, varies in the varying portion as a function of position. On the other hand, the deflection direction or the deflection angle is preferably constant even in the varying portion.

[0010] The fact that the deflection effect on the beam component of the laser beam for each position in the constant portion is independent of the distance of the position from the neutral region means that there is a constant deflection effect in the constant portion that is independent of the position. Thus, in the constant portion, in particular not only the deflection angle or the deflection direction but also the strength of the deflection is or intensity It is independent of position and therefore constant.

[0011] The deflection effect in the variation portion varies depending on the distance from the neutral region, in particular means that positions of the variation portion at equal distances from the neutral region have equal deflection effects, in particular equal deflection strengths. On the other hand, positions at different distances from the neutral region preferably have different deflection effects, in particular different deflection strengths.

[0012] The distance of the position in the change section from the neutral region is preferably measured perpendicularly to an imaginary or real dividing line between the change section and the neutral region. In this case, the distance is measured in particular depending on the shape or geometry of the imaginary or real dividing line or the neutral region. For example, if the neutral region is circular, the distance is preferably measured radially relative to the circular neutral region. On the other hand, if the neutral region is rectangular, for example, the distance is preferably measured perpendicularly to the boundary edge of the neutral region.

[0013] The neutral region can be designed in particular as a circle, ellipse or oval, or as a rectangle, or as any other geometric shape. It is preferably adapted to the cross-sectional geometry of the laser beam to be filtered. The shape of the deflection region preferably corresponds to the shape of the neutral region. This applies in particular not only to the constant part but also to the variable part.

[0014] According to a preferred embodiment, the variable portion is arranged between the neutral region on the one hand and the constant portion on the other hand. Advantageously, there is therefore a transition from the neutral region to the constant portion of the deflection effect, in particular a transition from a 0% deflection effect in the neutral region to a 100% deflection effect in the constant portion, preferably a continuous transition or a steady transition, in particular a linear transition or a Gaussian transition, in particular in the form of a semi-Gaussian function. In particular, in this way, undesired beam components that overlap the main beam or the useful beam can be filtered out without excessively impairing or reducing the main beam or the useful beam.

[0015] According to a preferred embodiment, the deflection region adjoins a shielding region in which the laser beam is absorbed. In this way, beam components outside the beam to be filtered can be shielded.

[0016] According to an extension of the invention, the neutral region is arranged centrally and is surrounded by the deflection region on the outside, in particular on the radial outside. Here, the variable portion is arranged radially between the neutral region and the constant portion. The neutral region is correspondingly, in particular, a central neutral region, to which the deflection region adjoins on the radial outside, the deflection region preferably having a constant portion as an outer constant portion and a variable portion as an inner variable portion. Accordingly, viewed in the radial direction, first the neutral region, then the variable portion and finally the constant portion follow one another from the radial inside to the radial outside. This represents a particularly simple configuration of the spatial frequency filter device.

[0017] Alternatively, it is possible that the neutral region is arranged radially on the outside and the deflection region adjoins the neutral region radially on the inside, wherein here too the variable portion is arranged between the neutral region and the constant portion. In this case, the constant portion is in particular a central constant portion, to which the variable portion adjoins radially on the outside, and the neutral region in turn adjoins the variable portion radially further on the outside. This configuration, which is almost the opposite of the configuration described above, also represents a very suitable possibility for filtering laser beams.

[0018] According to an extension of the invention, it is provided that, in the changing portion, the deflection effect on the beam component of the laser beam increases with increasing distance from the neutral region. This (as already indicated) is particularly advantageous since it allows filtering of undesired beam components overlying the main beam or the useful beam in a particularly suitable manner without excessively damaging the main beam or the useful beam itself, wherein in particular undesired effects (such as diffraction at the edges) are avoided or at least reduced. As also described above, in the changing portion, the deflection effect increases from the neutral region to the constant portion, preferably from 0% at the boundary of the neutral region or in the transition region to 100% at the boundary of the constant portion or in the transition region. Here, a value of 0% corresponds to a deflection effect present in the neutral region, i.e. preferably no deflection effect, and a value of 100% corresponds to a deflection effect present in the constant portion. Particularly preferably, in the changing portion, the deflection effect increases continuously or steadily with increasing distance from the neutral region, most particularly preferably linearly.

[0019] According to one embodiment of the invention, the deflection region has a phase influencing structure. Preferably, the amplitude of the laser radiation is not influenced in the deflection region. In a preferred embodiment, the deflection region thus acts only on the phase of the laser radiation. The phase influencing structure is preferably constant in the constant part, while in the variable part it varies in a position-dependent manner, in particular as a function of the distance from the neutral region, with respect to at least one property. Suitable phase-influencing structures are disclosed, for example, by Farn, MW, “Binary gratings with increased efficiency,” Appl. Opt. 31(22), 4453-4458 (1992); Ngcobo, S. et al., “A digital laser for on-demand laser modes,” Nat. Commun. 4:2289 doi:10.1038 / ncomms3289 (2013); and Eckstein W. et al., “Comparison of different simulation methods for effective medium computer generated holograms,” Opt. Express 21(10), 12424-12433 (2013).

[0020] According to one embodiment of the invention, the phase influencing structure is designed as a diffractive deflection structure. The diffractive deflection structure is periodic, has a defined, preferably constant modulation period, and has a constant modulation amplitude in a constant range, wherein the modulation period and the modulation amplitude determine the phase influencing of the laser radiation by the diffractive deflection structure. The modulation amplitude determines in particular the strength of the phase influencing, which is also referred to as phase modulation. In the varying part, the modulation amplitude of the diffractive deflection structure changes.

[0021] According to a preferred embodiment, the diffractive deflecting structure is formed as a geometrical grating. In this case, the modulation amplitude of the diffractive deflecting structure is understood to mean the geometrical height or depth of the diffractive deflecting structure, preferably measured along the beam axis. The modulation amplitude is then the grating height of the geometrical grating.

[0022] According to another preferred configuration, the diffraction deflection structure is composed of a refractive index position Changes, especially spatial Particularly preferably, the diffraction-deflecting structure is designed as a volume grating.

[0023] The modulation period is in particular the period length of the diffractive deflection structure measured perpendicularly to the beam axis, ie in the radial direction. The modulation period is preferably constant both in the constant part and in the varying part, in particular identical in the constant part and in the varying part.

[0024] According to one embodiment of the invention, it is provided that the deflection effect on the beam component of the laser beam varies in the variation part according to a defined function of the distance from the neutral region. In this way, the deflection effect and thus the overall performance of the spatial frequency filter arrangement can be advantageously influenced in a well-defined manner. As already mentioned, a preferred configuration of this variation of the deflection effect is a linear function. However, according to another configuration, it is also possible that the defined function is a Gaussian function. Other defined functions are also possible.

[0025] According to an extension of the invention, the spatial frequency filter device has a filter body on which the neutral region is constructed. The deflection region is applied to the filter body or introduced into the filter body. This represents a particularly easy to provide and at the same time very effective configuration of the spatial frequency filter device. The filter body, in particular the substrate, preferably has a material that is configured to be transmissive or reflective for laser radiation. The diffraction deflection structure is particularly preferably applied to the filter body or introduced into the filter body. The deflection region / diffraction deflection structure is particularly preferably produced by local changes, in particular structuring, of the material of the filter body, in particular the filter body.

[0026] According to one embodiment of the invention, the neutral region has a neutral width dimension. The neutral width dimension is in particular a half-width dimension, ie a dimension which specifies the half-width or ring width, in particular the radius.

[0027] The neutral width dimension is preferably at least 5% and at most 130% of the beam width dimension of the laser beam to be filtered.

[0028] In this case, the beam width dimension of the laser beam to be filtered is preferably also the half-width dimension, in particular the radius. In the case of a Gaussian laser beam, this is preferably from the beam axis to the point where the laser radiation has fallen to 1 / e of the maximum intensity on the beam axis. 2 The beam width dimension is measured as a fraction of the position.

[0029] According to a preferred embodiment, the neutral width dimension is preferably at least 20% to at most 60% of the beam width dimension. This value range has proven to be particularly advantageous for filtering undesired beam components that overlap with the main beam or useful beam.

[0030] According to another preferred embodiment, the neutral width dimension is preferably at least 60% to at most 100% of the beam width dimension. This value range has proven to be particularly advantageous for filtering undesired beam components which do not overlap or only overlap to a slight extent with the main beam or useful beam.

[0031] Alternatively or additionally, the varying portion preferably has a varying width dimension. The varying width dimension is also in particular a half-width dimension or a ring width, in particular a radius. The varying width dimension is preferably at least 10% to at most 150% of the neutral width dimension.

[0032] According to a preferred embodiment, the variable width dimension is at least 10% to at most 40%, preferably 30% of the neutral width dimension. This has proven to be particularly advantageous for filtering undesired beam components that only slightly overlap or do not overlap with the main beam or useful beam.

[0033] According to another preferred embodiment, the variable width dimension is at least 40% to at most 150%, preferably 100%, of the neutral width dimension. This embodiment has proven to be particularly advantageous for filtering undesired beam components overlapping the main beam or useful beam.

[0034] If the area is designed as annular, the corresponding width dimension is preferably the ring width, that is to say the entire width of the ring measured in a defined direction perpendicular to the boundary line of the ring, and thus approximately the radius of the outer ring approximately falling within the ring area. The radius portion on the .

[0035] According to one embodiment of the invention, the spatial frequency filter device is designed as a transmission stop, a lens, a protective glass, a fiber end cap or a mirror. These represent a particularly suitable embodiment of the spatial frequency filter device.

[0036] According to one embodiment of the invention, the diffraction-deflecting structure is designed in such a way that no zero diffraction order is produced, ie no zero-order diffraction occurs. Undesired beam components are thus deflected as completely as possible from the beam axis.

[0037] The diffraction-deflecting structure is preferably designed in such a way that it generates only the first diffraction order, that is to say only a first order of diffraction. Undesired beam components are thus deflected to a well-defined solid angle, where they can be filtered out in an easy and accurate manner.

[0038] According to a preferred embodiment, the diffractive deflecting structure has a blazed grating or is designed as a blazed grating. This represents a simple and practical embodiment of the diffractive deflecting structure.

[0039] According to one embodiment of the invention, it is provided that the diffractive deflecting structure is etched into the filter body. In this way, the diffractive deflecting structure can be produced very easily and with high accuracy.

[0040] Alternatively, the diffractive deflection structure is preferably introduced into the filter body as a volume modification, in particular as a volume grating. In this way, modifications can be produced with high accuracy in the volume of the filter body, in particular the volume of the substrate, wherein ultimately regions with different refractive indices are obtained, which act diffractingly.

[0041] The object is also achieved by providing a spatial frequency filter arrangement for a laser beam, which has a spatial frequency filter device according to the invention or a spatial frequency filter device according to one of the above-described embodiments. In addition, the spatial frequency filter arrangement has a constant filter device. With the help of the constant filter device, undesired beam components deflected by the spatial frequency filter device can be filtered out, particularly preferably shielded, in particular absorbed. In combination with the spatial frequency filter arrangement, the advantages already explained in combination with the spatial frequency filter device are obtained.

[0042] A constant filter is understood here to mean a device which has only a neutral region on the one hand and a shielding region adjoining the neutral region on the other hand. It is possible here that the neutral region is designed as a central neutral region which is surrounded radially on the outside by the shielding region. However, the opposite arrangement is also possible, in which the neutral region surrounds the central shielding region radially on the outside. Here, the neutral region transmits or reflects the laser radiation as undisturbed as possible, preferably completely undisturbed, while the shielding region preferably neither transmits nor reflects the laser radiation, preferably absorbs the laser radiation. Therefore, the constant filter has in particular no deflection region, in particular neither a constant part nor a variable part.

[0043] The constant filter device is preferably designed as a diaphragm, in particular as an aperture diaphragm.

[0044] According to a preferred embodiment, the constant filter device is arranged downstream of the spatial frequency filter device, as viewed in the beam propagation direction of the laser beam.

[0045] The constant filter device is particularly preferably arranged at a distance from the spatial frequency filter device, preferably at a certain propagation distance. The beam components deflected by the deflection region of the spatial frequency filter device are then advantageously screened by the constant filter device, because they propagate at an increased divergence angle compared to the desired main beam or useful beam, so that after a certain propagation distance they are spatially sufficiently separated from the main beam or useful beam and can therefore be eliminated, in particular absorbed, by the constant filter device.

[0046] In this way, the spatial frequency filter arrangement is designed in particular for amplitude filtering of the laser beam.

[0047] According to one embodiment of the invention, the spatial frequency filter arrangement has a first converging lens, which is arranged behind the spatial frequency filter arrangement in the beam propagation direction of the laser beam. The laser radiation filtered by the spatial frequency filter arrangement can be influenced in an advantageous manner by means of the converging lens. Preferably, the first converging lens is arranged in front of the constant filter arrangement, as seen in the beam propagation direction of the laser beam. In this way, the laser radiation can be imaged in particular onto the constant filter arrangement by means of the first converging lens, in order to achieve particularly effective filtering.

[0048] Alternatively, it is possible that the constant filter device can be integrated in the first converging lens or that the first converging lens is designed as a constant filter device. The first converging lens can be designed in particular to be opaque in the radially outer region or to be limited in its lens effect; or the lens effect is ineffective in the radially outer region; or the first converging lens is arranged in a housing, wherein the housing forms a shielding area. The first converging lens can also be surrounded by a cooled absorber or be arranged on a cooled absorber, which provides a shielding area.

[0049] According to an embodiment of the invention, the spatial frequency filter device has a second converging lens as an alternative or in addition to the first converging lens, which is arranged in front of the spatial frequency filter device in the beam propagation direction of the laser beam. This second converging lens can advantageously widen the laser beam in front of the spatial frequency filter device. This proves to be particularly advantageous if the laser beam has a very small beam diameter, so that (without the second converging lens) the spatial frequency filter device would require very small structural dimensions. If the laser beam is widened in this case, the spatial frequency filter device can have a correspondingly larger structure and can therefore be manufactured more easily and at a lower cost. Therefore, if the laser radiation leaves or is coupled out of the fiber bundle before the spatial frequency filter device and therefore has a particularly small beam diameter, it is particularly advantageous to provide a second converging lens. Generally, the beam width dimension can be matched to the outer diameter of the spatial frequency filter device by means of the second converging lens, in particular to make it smaller or larger. This also proves to be advantageous if the beam diameter is larger than the outer diameter of the spatial frequency filter device.

[0050] Alternatively or additionally, the spatial frequency filter arrangement preferably has a third focusing lens, which is arranged behind the constant filter arrangement in the beam propagation direction of the laser beam. This can be used (alone or in combination with the first focusing lens and / or the second focusing lens) to influence the laser beam, in particular to shape it, at the exit of the spatial frequency filter arrangement for the rear element or the workpiece to be processed. The laser beam can be collimated in particular by the third focusing lens.

[0051] According to a particularly preferred embodiment, the spatial frequency filter arrangement has a so-called 4f arrangement, wherein 4f stands for four focal lengths In the case of this design, in particular the following elements are arranged one behind the other in the order specified in the beam propagation direction: spatial frequency filter means, first focusing lens, constant filter means and third focusing lens. In this case, the constant filter means on the one hand and the spatial frequency filter means on the other hand are preferably arranged at the focus of the first focusing lens, wherein preferably the constant filter means is additionally arranged at the focus of the third focusing lens. With this arrangement, the laser radiation can be filtered particularly well and preferably collimated at the same time.

[0052] It is possible that in this 4f arrangement the second converging lens is arranged in front of the spatial frequency filter arrangement in the beam propagation direction. However, it is also possible that the spatial frequency filter arrangement in this preferred configuration does not have a second converging lens.

[0053] The object is finally also achieved by providing a method for spatial frequency filtering of a laser beam, wherein the laser beam radiates through a neutral region of a spatial frequency filter device, or wherein the laser beam is reflected by a neutral region of a spatial frequency filter device. In a deflection region radially adjacent to the neutral region, a beam component of the laser beam is deflected from the beam axis of the laser beam. In a constant part of the deflection region, the beam component is deflected with a constant deflection effect that is independent of the distance from the neutral region. In a variable part of the deflection region (in particular, arranged between the neutral region and the constant part), the beam component is deflected with a variable deflection effect as a function of the distance from the neutral region. Particularly preferably, in the variable part, the beam component is deflected as a function of the distance from the neutral region with a deflection effect that increases as the distance from the neutral region increases.

[0054] In conjunction with this method, in particular the advantages already explained in conjunction with the spatial frequency filter device and the spatial frequency filter arrangement result.

[0055] In a preferred embodiment, a spatial frequency filter arrangement according to the invention or a spatial frequency filter arrangement according to one of the above-described embodiments is used within the scope of the method. Alternatively or additionally, a spatial frequency filter arrangement according to the invention or a spatial frequency filter arrangement according to one of the above-described embodiments is used within the scope of the method. The advantages already described are obtained in a particular way here.

[0056] According to one embodiment of the invention, it is provided that the deflection region has a diffractive deflection structure. Preferably, the zero diffraction order is suppressed by the diffractive deflection structure. Particularly preferably, only the first diffraction order is generated by the first diffractive deflection structure.

[0057] According to one embodiment of the invention, it is provided that the beam component deflected in the deflection region is deflected away from the beam axis of the laser beam by a deflection angle, which is obtained in particular according to the following formula as the arcsine of the quotient of the wavelength of the laser radiation divided by the modulation period of the deflection region, in particular the modulation period of the diffractive deflection structure:

[0058]

[0059] Here, θ is the deflection angle, λ is the wavelength of the laser radiation, and g is the modulation period of the deflection region. Preferably, the deflection angle is approximated as the quotient of the wavelength of the laser radiation and the modulation period, in particular according to the following formula:

[0060]

[0061] For example, if the modulation period is 10 μm, the deflection angle for infrared radiation is approximately 5.7°. For green light, it is approximately half that.

[0062] Preferably, the beam component deflected by the deflection region of the spatial frequency filter means is eliminated, in particular absorbed, by constant filter means arranged spaced apart from the spatial frequency filter means, preferably spaced apart by a certain propagation distance.

[0063] In this way, in particular amplitude filtering is performed on the laser beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The invention is explained in more detail below based on the accompanying drawings, in which:

[0065] FIG1 shows a schematic illustration of a spatial frequency filter arrangement according to the prior art;

[0066] Figure 2 shows a schematic illustration of an embodiment of a spatial frequency filter arrangement according to the invention;

[0067] Figure 3a schematic diagram showing a first embodiment of a spatial frequency filter arrangement, and

[0068] Figure 4 A schematic illustration of a second embodiment of a spatial frequency filter arrangement is shown. DETAILED DESCRIPTION

[0069] 1 shows a schematic representation of a spatial frequency filter arrangement 100 according to the prior art. The spatial frequency filter arrangement 100 is provided for use with a laser beam 200, which is coupled out of a fiber or fiber bundle 10, for example. The laser beam 200 is a diverging laser beam. However, such a spatial frequency filter arrangement 100 can also be used for use with a collimated laser beam 200.

[0070] The spatial frequency filter arrangement 100 has a neutral region 110 which is provided here for transmitting the laser beam 200 . However, the neutral region 110 can also be provided for reflecting the laser beam 200 .

[0071] The neutral region 110 is adjoined by a deflection region 120 which is provided to deflect a beam component 210 of the laser beam 200 from a beam axis A of the laser beam 200. This results in a total deflection angle β, which comprises, on the one hand, a deflection angle θ determined by the deflection region 120 and, on the other hand, an opening angle of the diverging laser beam 200. If the laser beam 200 is designed as a collimated laser beam, it is only deflected by a deflection angle θ by the deflection region 120. The beam component 210 deflected by the deflection region 120 is then screened by the constant filter device 320. This is possible because the deflected beam component propagates at an increased divergence angle compared to the desired main beam or useful beam and is therefore spatially sufficiently separated from the main beam or useful beam after a certain propagation distance and can therefore be eliminated by the constant filter device 320, in particular by a conventional absorption element.

[0072] In the case of the spatial frequency filter arrangement 100 known from the prior art, the deflection effect of the deflection region 120 is independent of position, ie is constant everywhere in the deflection region 120 .

[0073] Figure 2A schematic illustration of an embodiment of a spatial frequency filter device 100 is shown. Identical or functionally identical elements are provided with the same reference numerals in all the figures, so that reference is hereby made to the above description in each case. The spatial frequency filter device 100 differs from the known spatial frequency filter device 100 according to FIG. 1 in particular in that here the deflection region 120 has, in addition to a constant portion 123, a variable portion 125 in which, for each position in the constant portion 123, the deflection effect on the beam component 210 of the laser beam 200 is independent of the distance of the position from the neutral region 110, and in which the deflection effect on the beam component 210 of the laser beam 200 varies as a function of the distance from the neutral region 110. In this way, in particular also those beam components 210 which are arranged close to the main beam or the useful beam or overlap with the main beam or the useful beam can be filtered out without inappropriately impairing or adversely influencing the main beam or the useful beam. The change in the deflection effect here relates in particular to the deflection efficiency, in particular the strength of the phase modulation. In contrast, the deflection angle is preferably constant independently of the position and in particular is identical in the constant portion 123 and the varying portion 125 .

[0074] The varying portion 125 is in particular arranged between the neutral region 110 and the constant portion 123 .

[0075] In the case of the embodiment shown here, the neutral region 110 is arranged centrally, wherein the deflection region 120 radially adjoins the neutral region 110. Here, the deflection region 120 has a constant portion 123 as an outer constant portion and a variable portion 125 as an inner variable portion, wherein the variable portion 125 adjoins the neutral region 110 radially on the inside, wherein the constant portion 123 adjoins the variable portion 125 radially on the outside. Preferably, the individual regions / portions are designed in a circular manner, the variable portion 125 preferably surrounds the central neutral region 110 in the form of a ring, and wherein the constant portion 123 in turn surrounds the variable portion 125 in the form of a ring radially on the outside, so that the variable portion 125 is arranged as an annular region between the neutral region 110 (especially designed in the form of a disk) and the annular constant portion 123 (designed as an outer ring).

[0076] However, an opposite configuration is also possible, in which the constant portion 123 of the deflection region 120 is arranged centrally and is then directly adjoined radially outwardly by the variable portion 125 and in turn by the outer neutral region 110 .

[0077] In the variation section 125 , the deflection effect on the beam component 210 of the laser beam 200 preferably increases with increasing distance from the neutral region 110 .

[0078] Preferably, in the variation section 125 , the deflection effect on the beam component 210 varies according to a certain function of the distance from the neutral region 110 , particularly preferably according to a Gaussian function or according to a linear function.

[0079] The deflection region 123 preferably has a phase influencing structure 126 which is constant in the constant portion 123 and varies in the varying portion 125. Particularly preferably, the spatial frequency filter arrangement 110 only influences the phase, but not the intensity or amplitude of the laser beam 200. This has the advantage that the laser beam 200 ultimately has the same intensity distribution behind the spatial frequency filter arrangement 100 in the beam propagation direction as in front of the spatial frequency filter arrangement 100 (except for the filtered, undesired beam components 210).

[0080] The phase-influencing structure 126 is preferably designed as a diffractive deflection structure 127, wherein the diffractive deflection structure 127 has a modulation period g and is therefore periodic, wherein in the constant portion 123 it has a constant modulation amplitude a. In contrast, in the varying portion 125 the modulation amplitude a of the diffractive deflection structure 127 varies. Preferably, the modulation amplitude a varies in the varying portion 125 according to a specific function of the distance from the neutral region 110, in particular according to a Gaussian function or according to a linear function.

[0081] The diffractive deflecting structure 127 can be designed in particular as a geometrical grating or can be formed by a local variation, in particular a spatial variation, of the refractive index.

[0082] The spatial frequency filter arrangement 100 preferably has a filter body 130 on which the neutral region 110 is formed. The deflection region 120 is preferably applied to the filter body 130 or introduced into the filter body 130 .

[0083] Figure 2 , the neutral region 110 also has a neutral width dimension NB. Here, the neutral width dimension NB is preferably the radius of the neutral region 110.

[0084] The spatial frequency filter device 100 is preferably designed as a transmission aperture, a lens, a protective glass, a fiber end cap or a mirror. The spatial frequency filter device 100 can in particular also be integrated in the resonator of the laser generating the laser beam 200, arranged downstream of the resonator or arranged upstream of or in the processing optical unit. However, it is also possible to design the spatial frequency filter device 100 as a separate element.

[0085] The diffraction deflection structure 127 is preferably designed in such a way that it does not produce a zero-order diffraction. The diffraction deflection structure 127 is preferably designed in such a way that it only produces a first-order diffraction, in particular no higher diffraction orders. According to a preferred embodiment, the diffraction deflection structure 127 is designed as a blazed grating 129 or it has a blazed grating 129.

[0086] According to a preferred embodiment, the diffraction-deflecting structure 127 is etched into the filter body 130 or introduced into the filter body 130 as a volume modification, in particular as a volume grating.

[0087] Figure 3 A schematic illustration of a first embodiment of a spatial frequency filter arrangement 300 for a laser beam 200 is shown, wherein the spatial frequency filter arrangement 300 has a spatial frequency filter device 100 in accordance with the technical teaching disclosed herein. Here, it is shown on the spatial frequency filter device 100 that the variation section 125 has a variation width dimension VB, which is preferably the ring width of the annular variation section 125, which surrounds the neutral region 110 in the form of a ring by the ring width.

[0088] Figure 3 Also schematically shown in FIG. 1 is a beam width dimension SB of the laser beam 200, which is also configured as a half-width dimension, here the beam radius, wherein in particular twice the beam width dimension is Figure 3 2 is shown as the diameter of the laser beam 200. In the case of the laser beam 200 shown here as a Gaussian beam, the beam width dimension is preferably 1 / e of the maximum intensity. 2 The score is determined by the circumstances.

[0089] The neutral width dimension NB is preferably at least 5% to at most 130% of the beam width dimension SB. The varying width dimension VB of the varying portion 125 may alternatively or additionally preferably be at least 10% to at most 150% of the neutral width dimension NB.

[0090] Figure 3 Schematically, the following situation is shown, in which the undesired beam components 210 are at a considerable distance from the beam axis A and at the same time at a considerable distance from the main beam or useful beam, so that they can be filtered out quite easily. In this case, the neutral width dimension NB is preferably at least 60% to at most 100% of the beam width dimension SB. The variation width dimension VB is preferably at least 10% to at most 40%, preferably 30%, of the neutral width dimension NB.

[0091] Reference has been made here Figure 4, wherein (irrespective of the other different configurations of the second embodiment of the spatial frequency filter arrangement 300 shown there) the following situation is shown: in which the undesired beam component 210 overlaps the main beam or the useful beam and is therefore less than according to Figure 3 The case shown in is arranged closer to the beam axis A. In this case, it is more difficult to filter out undesired beam components. In this case, the neutral width dimension NB is preferably selected to be at least 20% to at most 60% of the beam width dimension SB. In this case, the variable width dimension VB is preferably at least 40% to at most 150%, preferably 100%, of the neutral width dimension NB.

[0092] Return to Figure 3 , where the spatial frequency filter arrangement 300 shown has a constant filter device 320 behind the spatial frequency filter device 100 in the beam propagation direction of the laser beam 200 (in particular at a certain propagation distance from the spatial frequency filter device). It also has a first focusing lens 310 arranged behind the spatial frequency filter device 100. In addition, the first focusing lens 310 is arranged in front of the constant filter device 320. Alternatively, the constant filter device 320 can also be integrated in the first focusing lens 310 or arranged on the first focusing lens 310. The undesired beam components deflected by the deflection region 120 are eliminated, in particular absorbed, by the constant filter device 320 after they have traveled a certain propagation distance. In this way, in particular amplitude filtering of the laser beam 200 is achieved.

[0093] According to Figure 3 The spatial frequency filter arrangement 300 of the first exemplary embodiment shown furthermore has a second converging lens 330, which is arranged in front of the spatial frequency filter device 100 in the beam propagation direction of the laser beam 200. It has proven to be particularly advantageous if the laser beam 200 has a very small beam width dimension SB, in particular coupled out of the optical fiber bundle 10, wherein the laser beam can then be widened by the second converging lens 330, so that the spatial frequency filter device 100 can have a larger structural dimension, in particular a larger modulation period g and / or a larger modulation amplitude a than if the laser beam 200 had not been widened. In general, the beam width dimension SB can be adapted to the outer diameter of the spatial frequency filter device 100, in particular reduced or enlarged, by means of the second converging lens 330. It has also proven to be advantageous if the beam width dimension SB is greater than the outer diameter of the spatial frequency filter device 100.

[0094] In the case of the first exemplary embodiment shown here, the spatial frequency filter arrangement 300 also has a third focusing lens 340, which is arranged behind the constant filter device 320 in the beam propagation direction of the laser beam 200. This lens can be used particularly advantageously to collimate the filtered laser beam. This results in a filtered and collimated laser beam 220 behind the spatial frequency filter arrangement 300. It is schematically shown here that such a filtered and collimated laser beam 220 no longer has undesired beam components 210.

[0095] exist Figure 3 and Figure 4 , the laser beam 200 propagates through the spatial frequency filter arrangement 300 from left to right, respectively.

[0096] Figure 4 A schematic illustration of a second embodiment of a spatial frequency filter arrangement 300 is shown. The second embodiment shown here does not have a second converging lens 330. However, it is also possible to use such a second converging lens 330 in the case of this second embodiment.

[0097] Preferably, the spatial frequency filter device 100 is constructed according to the so-called 4f arrangement, wherein the spatial frequency filter device 100 and the constant filter device 320 are respectively arranged at the focal positions on both sides of the first converging lens 310, wherein in addition, the constant filter device 320 is preferably arranged at the focus of the third converging lens 340.

[0098] In accordance with Figure 3 In the case of the first embodiment, the spatial frequency filter device 100 is additionally arranged at the focus of the second focusing lens 330. However, this does not necessarily have to be the case, but an arrangement outside the focus is also possible, in particular in order to adapt the beam width dimension SB to the outer diameter of the spatial frequency filter device 100.

[0099] According to a preferred embodiment, the focal points (Foki) of the individual converging lenses 310 , 330 , 340 are designed identically, but can also be selected to be different in pairs or to be completely different from one another.

[0100] The laser beam 200 is preferably filtered in that the laser beam 200 radiates through the neutral region 110 of the spatial frequency filter device 100 or the laser beam 200 is reflected by the neutral region 110. In this case, the undesired beam component 210 is deflected from the beam axis A in a deflection region 120 radially adjacent to the neutral region 110, wherein the beam component 210 is deflected in a constant portion 123 with a constant deflection effect that is independent of the distance from the neutral region 110, wherein the beam component 210 is deflected in a variable portion 125 as a function of the distance from the neutral region 110 with a variable deflection effect (in particular a deflection effect that increases as the distance from the neutral region 110 increases).

[0101] The deflection angle θ of the deflection region 120 is preferably determined, in particular, according to the formula (1) specified above, as the arcsine of the quotient of the irradiation wavelength λ of the laser beam 200 on the one hand and the modulation period g of the deflection region 120 on the other hand. Approximately, the deflection angle θ is preferably determined, in particular, according to the formula (2) specified above, as the quotient of the irradiation wavelength λ divided by the modulation period g.

[0102] In a plane perpendicular to the beam axis A, the neutral region 110 is preferably geometrically shaped such that it corresponds at least to the ideal beam geometry of the laser beam 200, in particular to a circular shape for a cylindrically symmetrical laser beam 200. However, it can also be rectangular, in particular for a rectangular laser beam cross section, or elliptical, in particular for an elliptical laser beam cross section. The deflection region 120, in particular both the constant portion 123 and the variable portion 125, is preferably shaped like the neutral region 110 and surrounds the neutral region radially on the outside as a correspondingly shaped peripheral region.

Claims

1. A spatial frequency filter arrangement (300) for a laser beam (200), the spatial frequency filter arrangement comprising a spatial frequency filter device (100), a first focusing lens (310) and a constant filter device (320), the first focusing lens being arranged behind the spatial frequency filter device (100) in the beam propagation direction of the laser beam (200), wherein: The spatial frequency filter device (100) comprises: a neutral region (110) which is arranged to transmit or reflect the laser beam (200), wherein in the neutral region the laser beam is transmitted or reflected undisturbed, that is, a beam component of the laser beam is not deflected from the beam axis, and a deflection region (120) radially adjacent to the neutral region (110) which is arranged to deflect a beam component (210) of the laser beam (200) from the beam axis (A) of the laser beam (200), wherein the deflection region (120) has a constant portion (123) in which, for each position in the constant portion (123), the deflection effect on the beam component (210) of the laser beam (200) is independent of the distance of the position from the neutral region (110), and wherein the deflection region (120) has a variable A portion (125) in which the deflection effect on the beam component (210) of the laser beam (200) varies depending on the distance from the neutral region (110), wherein the neutral region (110) is arranged centrally and is surrounded on the outside by the deflection region (120), and the varying portion (125) is arranged between the neutral region (110) and the constant portion (123), wherein the constant filter device (320) is configured to filter out the beam component (210) of the laser beam (200) deflected by the spatial frequency filter device (100).

2. The spatial frequency filter arrangement (300) according to claim 1, characterized in that In the changing portion (125), a deflection effect on a beam component (210) of the laser beam (200) increases with increasing distance from the neutral region (110).

3. The spatial frequency filter arrangement (300) according to claim 1 or 2, characterized in that The deflection region (120) has a phase influencing structure (126).

4. The spatial frequency filter arrangement (300) according to claim 3, characterized in that The phase influencing structure (126) is designed as a diffractive deflection structure (127), wherein the diffractive deflection structure (127) is periodic and has a constant modulation amplitude (a) in the constant portion (123), wherein the modulation amplitude (a) of the diffractive deflection structure (127) varies in the varying portion (125).

5. The spatial frequency filter arrangement (300) according to claim 1 or 2, characterized in that A deflection effect on a beam component (210) of the laser beam (200) varies as a function of a certain distance from the neutral region (110).

6. The spatial frequency filter arrangement (300) according to claim 1 or 2, characterized in that The spatial frequency filter device (100) has a filter body (130), on which the neutral region (110) is formed, wherein the deflection region (120) is applied to the filter body (130) or introduced into the filter body (130).

7. The spatial frequency filter arrangement (300) according to claim 1 or 2, characterized in that The neutral region (110) has a neutral width dimension (NB), wherein a) the neutral width dimension (NB) is 5% to 130% of the beam width dimension (SB) of the laser beam (200) to be filtered, and b) the variation width dimension (VB) of the variation portion (125) is 10% to 150% of the neutral width dimension (NB).

8. The spatial frequency filter arrangement (300) according to claim 1 or 2, characterized in that The spatial frequency filter device (100) is constructed as a transmission diaphragm, a lens, a protective glass, an optical fiber end cap or a reflective mirror.

9. The spatial frequency filter arrangement (300) according to claim 4, characterized in that The diffractive deflecting structure (127) is etched into the filter body (130) or introduced as a volume modification into the filter body (130).

10. The spatial frequency filter arrangement (300) according to claim 1 or 2, characterized in that A second converging lens (330) is arranged in front of the spatial frequency filter device (100) in the beam propagation direction of the laser beam (200).

11. The spatial frequency filter arrangement (300) according to claim 5, characterized in that The function is a Gaussian function or a linear function.

12. The spatial frequency filter arrangement (300) according to claim 7, characterized in that The neutral width dimension (NB) is 20% to 60% or 60% to 100% of the beam width dimension (SB) of the laser beam (200) to be filtered.

13. The spatial frequency filter arrangement (300) according to claim 7, characterized in that The varying width dimension (VB) of the varying portion (125) is 10% to 40% of the neutral width dimension (NB).

14. The spatial frequency filter arrangement (300) according to claim 13, characterized in that The varying width dimension (VB) of the varying portion (125) is 30% of the neutral width dimension (NB).

15. The spatial frequency filter arrangement (300) according to claim 7, characterized in that The varying width dimension (VB) of the varying portion (125) is 40% to 150% of the neutral width dimension (NB).

16. The spatial frequency filter arrangement (300) according to claim 15, characterized in that The varying width dimension (VB) of the varying portion (125) is 100% of the neutral width dimension (NB).

17. A method for spatial frequency filtering of a laser beam (200), wherein: Use of a spatial frequency filter arrangement (300) according to any one of claims 1 to 16, wherein a) the laser beam (200) radiates through the neutral region (110) of the spatial frequency filter arrangement (100), or b) the laser beam (200) is reflected by the neutral region (110) of the spatial frequency filter arrangement (100); wherein - a beam component (210) of the laser beam (200) radially adjacent to the neutral region (110) The laser beam (200) is deflected in the deflection region (120) from the beam axis (A), wherein: in the constant part (123) of the deflection region (120), the beam component (210) is deflected with a constant deflection effect that is independent of the distance from the neutral region (110), and wherein: in the variable part (125) of the deflection region (120), the beam component (210) is deflected with a variable deflection effect depending on the distance from the neutral region (110).

18. The method according to claim 17, characterized in that The deflection region (120) has a diffractive deflection structure (127), wherein the zeroth diffraction order is suppressed by the diffractive deflection structure (127).

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