DEVICE FOR COMBINATION OF AT LEAST TWO LASER BEAMS

Description

[0001] The invention addresses the problem of combining at least two input laser beams into a single effective beam with high power and high beam quality. Such techniques are used, for example, to generate high-power laser radiation for material processing purposes.

[0002] Various techniques are known for combining individual beams. Individual beams with different wavelengths can be combined into a single output beam using the principle of spectral coupling. For this purpose, an optical coupling element can be used which is spectrally selective and combines separately incident input beams with different wavelengths into a common output beam. In particular, the wavelength-dependent diffraction of light at a diffractive optical element can be exploited (i.e., the wavelength dependence of the diffraction angle at the diffractive optical element). The output beam is then broadband and contains the wavelengths of the input beams as spectral components. For many applications, this does not result in any disadvantages, especially when the power density and / or intensity of the output beam is primarily relevant.However, the beam quality is often crucial for the usability of the output beam. If possible, the beam quality of the input beams should be largely retained when combined to form the output beam.

[0003] Fiber lasers, for example, are very easy to handle laser sources. These are solid-state lasers in which the active medium is provided by a suitably designed light-conducting fiber (e.g., doped glass fiber). Such fiber lasers can deliver laser radiation with high beam quality. In single-mode operation (especially in fundamental mode), a beam quality M 2 < less than 1.2 is achievable. Fiber lasers are also characterized by long lifetimes and a robust design, as well as advantageous properties such as good coolability of the active medium and the possibility of continuous operation.

[0004] For fundamental reasons, laser light sources in practice have a certain bandwidth. This bandwidth is particularly significant in the aforementioned fiber lasers and is also present when operating in the fundamental mode. In fiber lasers, the bandwidth of the generated radiation generally increases with increasing power. Various effects can contribute to this, particularly nonlinear interactions in the amplifier fiber (e.g., stimulated Brillouin scattering, stimulated Raman scattering, or self-phase modulation).

[0005] In the beam combination mentioned above, a non-ideal bandwidth leads to a deterioration in the beam quality of the output beam due to spectral coupling. This is due, among other things, to the fact that a diffractive optical element imparts additional divergence to an input beam with a bandwidth due to the wavelength dependence of scattering. In this case, a non-zero bandwidth leads to a deformed beam cross-section, which, without compensation, degrades the beam quality of the output beam.

[0006] The document US 2009 / 153968 A1 discloses a known device for combining input laser beams.

[0007] The present invention is intended to enable the generation of high-intensity laser radiation with very good beam quality by combining multiple input beams. In particular, the use of laser radiation sources with non-ideal bandwidths should be possible while still achieving an output beam with good beam quality. In particular, the use of fiber lasers as input laser beam sources should also be enabled.

[0008] This object is achieved by a device for combining at least two input laser beams with the features of claim 1. Each of the input laser beams has a spectral bandwidth and accordingly comprises different spectral components, each with different wavelengths. The wavelengths of the input laser beam thus lie within a wavelength range characterized by the bandwidth. The device comprises at least one precompensation unit (in particular, several precompensation units) and a combination unit arranged downstream in the beam path.

[0009] The at least one precompensation unit detects one or more input laser beams. The precompensation unit has at least one diffractive (i.e., diffractive) optic, which expands the respective input laser beam into an associated, broadened intermediate beam bundle.

[0010] The combination unit is arranged such that it detects the intermediate beams fed by the input laser beams. The combination unit has at least a first diffractive optical element (DOE) and a second diffractive optical element (DOE), wherein the second diffractive optical element is arranged downstream of the first diffractive optical element in the beam path. The combination unit is coordinated with the at least one pre-compensation unit such that the first diffractive optical element converts each intermediate beam into a convergent beam with a beam waist by diffraction. Furthermore, the diffractive optical elements are arranged and configured such that said beam waist lies on the second diffractive optical element (i.e., is detected by the second diffractive optical element).The second diffractive optical element is then designed and arranged in such a way that all incident spectral components are deflected into a common radiation direction.

[0011] The pre-compensation unit thus generates a spatial beam broadening depending on the spectral bandwidth of the respective input laser beam, wherein the individual wavelength components are arranged along an expansion direction sorted with increasing wavelength. In this respect, the intermediate beam bundle is spatially broadened compared to the input laser beam, and the broadening occurs in such a way that the spectral components are spatially sorted and that the various spectral components are arranged spatially adjacent to one another with increasing wavelength. In other words, the various spectral components in the intermediate beam bundle have a spatial beam offset depending on the spectral distance from one another. In particular, the spectral components of the beam run adjacent to one another in one plane, i.e.The beam is preferably expanded such that the spectral components are spread out along the expansion direction and arranged in order of increasing wavelength. Short-wavelength components tend to be located on one side of the intermediate beam, while long-wavelength components tend to be located on the other side of the intermediate beam.

[0012] The combination unit is then designed and arranged such that it captures the adjacent spectral components, with the first diffractive optical element (DOE) diffracting all the spectral components toward a common beam waist. The beam waist is thus a convergence region of the bundle of the various spectral components. With appropriate matching of the pre-compensation unit and the combination unit, this can be achieved through the underlying diffraction effects. Due to the spatial expansion in the intermediate beam, the various spectral components impinge on the first diffractive optical element (DOE) of the combination unit at different positions.However, the first diffractive optical element is then designed in particular in such a way that the wavelength-dependent deflection occurs in such a way that the spectral components diffracted at the different positions converge again in the beam waist.

[0013] The second diffractive optical element (DOE) of the combination unit is then preferably matched to the precompensation unit and the first diffractive optical element such that the various spectral components are all diffracted in the same direction (namely, the emission direction). While the various spectral components impinge on the second diffractive optical element of the combination unit at different angles, the beam waist of the convergent spectral components lies on the second diffractive optical element. As a result, all spectral components are recombined into one output beam. This occurs for all spectral components of the at least two input laser beams, so that all input laser beams are combined into a common output beam.

[0014] Overall, the interaction of the pre-compensation unit and the combination unit allows beam broadening to be reversed according to the spectral bandwidth. This principle utilizes diffraction effects, and the beam parameter product or beam quality M 2< remains essentially unaffected. In particular, the output beam can have a beam quality that essentially corresponds to the beam quality of the input laser beams. In addition to the intrinsic (diffraction-limited) divergence of the laser beams, no additional beam broadening or divergence is introduced.

[0015] The invention thus enables the feeding of a high-power effective beam with multiple input laser beams, even if these have a non-ideal bandwidth. The input laser beams can therefore be provided by fiber lasers, even at high power levels. The optical elements involved can be constructed, in particular, using gratings (diffraction gratings) and, if necessary, plane mirrors. Such components can be manufactured with high precision and are also suitable for high radiation powers in continuous operation. Advantageously, the pre-compensation unit is designed and tuned to the wavelength of the input laser beam in such a way that all spectral components in the intermediate beam bundle run parallel to one another along a main direction. The input laser beam, and thus each spectral component, usually has an intrinsic divergence due to diffraction, which is characterized by the beam quality or the beam parameter product.The effective propagation direction of a spectral component can, however, be defined, for example, as an integral over all directional components of the local Poynting vectors of the various spectral components. The precompensation unit is preferably designed such that the preferred directions of all spectral components run parallel to one another, ie, the intermediate beam is parallelized with spatially adjacent spectral components.

[0016] The pre-compensation unit comprises several diffractive optical elements (DOEs).

[0017] According to the invention, the precompensation unit has at least a first and a second diffractive optical element.

[0018] In particular, the first diffractive optical element is designed such that the different spectral components of the input laser beam are diffracted in different directions, forming a divergent beam in the beam path between the first and second diffractive optical elements. The first diffractive optical element thus divides the broadband input laser beam into its spectral components. The first diffractive optical element is designed such that, for each spectral component, a specific diffraction order (preferably the first diffraction order), which is used to feed the intermediate beam, has a different diffraction angle.

[0019] For further refinement, the second diffractive optical element of the pre-compensation unit is then designed and arranged such that the different spectral components of the divergent beam are all deflected or diffracted in the same direction (namely, the aforementioned main direction). Due to the divergent path in front of the second diffractive optical element, the various beam components impinge on the second diffractive optical element at different positions and at different angles. However, since diffraction effects are wavelength-dependent, the diffractive optical elements can be coordinated such that the diffraction directions at the second diffractive intermediate element are the same for all spectral components. Due to the different impingement positions, the spectral components then run spatially offset from one another and parallel in the intermediate beam.

[0020] According to a general aspect of the invention, the pre-compensation unit is designed such that the intermediate beam bundle has a spatial width which is greater the larger the bandwidth of the input laser beam. In particular, the spatial width is proportional to the bandwidth of the input laser beam, which can be achieved, for example, in the case of diffraction at a grating in the range of small angles. In the present context, the spatial width is defined as the extent of the intermediate beam bundle perpendicular to the main direction (see above). Although the intrinsic beam divergence of the input laser beam also leads to a broadening of the beam cross-section along the beam path, this is not taken into account for the purposes of interpreting the aforementioned group of features.

[0021] The diffractive optics of the pre-compensation unit or the diffractive optical elements contained therein, as well as the diffractive optical elements of the combination unit, are generally optical diffraction elements that generate a wavelength-dependent beam deflection due to diffraction. According to an advantageous embodiment, the first diffractive optical element and the second diffractive optical element of the pre-compensation unit have matching angular dispersions. The angular dispersion refers in particular to the dependence of the diffraction angle on the wavelength, or the change in the diffraction angle with the wavelength. The angular dispersion indicates a measure of the wavelength splitting of a polychromatic wave by the diffractive optical element. In particular, the angular dispersion is defined as the change in the diffraction angle (α) with the wavelength (λ): Angular dispersion wd = dα / dλ.

[0022] The first diffractive optical element and the second diffractive optical element can be designed, for example, as reflection gratings. However, a design as a transmission grating is also conceivable. Various combinations of reflection gratings and transmission gratings can be advantageous here. For example, both gratings can be of the same type (reflection or transmission). The use of two reflection gratings enables a folded beam path and thus a short installation length or, in general, a small installation space. If one of the two diffractive optical elements or both diffractive optical elements are designed as transmission gratings, adjustment of the device can be simplified if necessary.

[0023] When using gratings, it is particularly advantageous if the first diffractive optical element and the second diffractive optical element have matching grating constants. Since the diffraction angles generally depend on the grating constant and the wavelength, this allows for the provision of diffractive optical elements with matching angular dispersion.

[0024] In the precompensation unit, the first diffractive optical element and the second diffractive optical element are preferably aligned with respect to one another and configured such that, upon diffraction of the input laser beam at the first diffractive optical element, the first diffraction orders for all spectral components of the input laser beam are respectively captured by the second diffractive optical element (i.e., impinge on the second diffractive optical element). For this purpose, in particular, the extent and the relative arrangement of the diffractive optical elements to one another are adapted to the input laser beam and its bandwidth.

[0025] The input laser beam is irradiated, in particular, along an incident beam direction onto the first diffractive optical element and diffracted there. For the various spectral components, the first order of diffraction impinges on the second diffractive optical element at different diffraction angles due to angular dispersion. The second diffractive optical element is then preferably dimensioned and aligned such that it absorbs the first order of diffraction of all spectral components and diffracts them into the intermediate beam.

[0026] For a further refinement, the first and second diffractive optical elements of the combination unit are aligned and configured with respect to one another such that, upon diffraction of the intermediate beam at the first diffractive optical element, the first order of diffraction is captured by the second diffractive optical element of the combination unit for all spectral components. As a result, the diffraction angles of the various diffractive optical elements are automatically coordinated such that the pre-compensated and expanded beam (intermediate beam) is automatically recombined into a beam with high beam quality and a small beam cross-section.

[0027] An advantageous, unclaimed embodiment results from the fact that the diffractive optical elements of the pre-compensation unit and the combination unit have matching dispersion properties, in particular matching angular dispersions. In this respect, it is advantageous if all diffractive optical elements of the device have matching dispersion properties. This can be achieved, for example, by the gratings of the pre-compensation unit and the combination unit having the same grating constants. This embodiment has the advantage, for example, that the expansion of the beam by the pre-compensation unit can be easily reversed with the combination unit. In this respect, the device can then be used for different bandwidths without the need for special adaptations. Overall, this results in a symmetrical structure.

[0028] It is according to the invention if the diffractive optical elements of the precompensation unit and the diffractive optical elements of the combination unit have angular dispersions that differ from one another.

[0029] The pre-compensation unit comprises (in particular in the beam path after the second diffractive optical element) and / or the combination unit (in particular in the beam path before the first diffractive optical element) an adaptation optics. The adaptation optics are designed to change convergence properties and / or divergence properties and / or a beam width. With such configurations, it is possible to use non-matching optical gratings and to carry out the necessary optical adjustments (spreading or convergence of the bundle) by means of lenses and / or mirrors. For example, the adaptation optics can comprise one or more planar deflecting mirrors. It is also conceivable for the adaptation optics to have a telescope with at least two lens means. The telescope can, for example, be designed as an anamorphic telescope, for example in order to generate orto adapt the beam expansion after the pre-compensation unit to the properties of the combination unit.

[0030] According to a fundamentally advantageous aspect of the invention, the device comprises a plurality of precompensation units, each with a diffractive optic. Preferably, each input laser beam is assigned a precompensation unit. This makes it possible to feed the output beam with a plurality of possibly broadband input laser beams.

[0031] However, it can also be advantageous for one precompensation unit to be effective for multiple input laser beams. This enables a compact design. For further refinement, the multiple precompensation units are designed and arranged such that the intermediate beam bundles generated by the various precompensation units all run parallel to one another. Therefore, the main directions defined above are preferably parallel to one another. This allows the various intermediate beam bundles to be fed into the combination unit in parallel.

[0032] In principle, the invention also relates to a device for generating a laser beam (namely the above-mentioned output beam), comprising at least two input laser sources for each emitting an input laser beam, as well as comprising a device for combining the input laser beams according to the type described herein. In these embodiments, separate laser branches are combined to form the output beam.

[0033] The invention is described in more detail below with reference to the figures.

[0034] They show: Figure 1: A sketched representation of a device for combining a plurality n of broadband input laser beams, comprising precompensation units (sketched representation) and a combination unit (sketched representation); Figure 2: A sketched representation of an exemplary embodiment of a device with a precompensation unit and a combination unit.

[0035] In the figures and in the following description, the same reference symbols are used for identical or corresponding features.

[0036] The Figure 1 1 shows a schematic representation of a device for generating a particularly high-energy laser beam (output beam 12), designated in its entirety by reference numeral 10. The device 10 comprises a plurality n of input laser sources 14-1, 14-2, ... 14-n-1, 14-n, each of which emits an input laser beam 16-1, 16-2, ...

[0037] Each input laser beam 16-1, 16-2, ..., has a certain spectral bandwidth and thus comprises various spectral components, each with a different wavelength λ x . The device 10 serves in particular to provide a high-energy output beam 12 with a beam quality M 2< that is as similar as possible to or corresponds to the beam quality M 2< of the individual input laser sources 14-1, 14-2, ...,. The input laser sources 14 can be designed, for example, as fiber lasers, which are operated in particular for emission in their fundamental mode and accordingly have a high beam quality. The respective input laser beams 16-1, 16-2, ... always have a certain intrinsic divergence due to diffraction, which naturally leads to beam broadening when propagated over longer distances.However, for the purposes of explaining the present invention, this effect will be neglected in the present description.

[0038] The radiation from the input laser sources 14-1, ..., 14-n enters a device 18 for combining several input laser beams 16-1, 16-2, ... The device 18 is explained in more detail below.

[0039] In the example shown, the device for combining the input laser beams 16-1, 16-2, ... comprises a plurality of precompensation units 20-1, 20-2, ..., 20-n, wherein each of the precompensation units 20 is assigned to an input laser beam 16 in the example shown and detects only the respectively assigned input laser beam 16. However, this configuration is not mandatory; it is also conceivable for one precompensation unit 20 to detect a plurality of input laser beams 16.

[0040] As explained in more detail below, each precompensation unit 20-1, 20-2, ... transforms the detected input laser beam 16-1, 16-2, ... into a respective, widened intermediate beam bundle 22-1, 22-2, ... In the intermediate beam bundle 22, the spectral components of the respective associated input laser beam 16 are no longer superimposed in a common beam, but are spatially arranged next to one another in a sorted manner with increasing wavelength (see below).

[0041] The intermediate beam bundles 22-1, 22-2, ... then run - if necessary via additional adaptation optics (see below) - into a combination unit 24. The combination unit 24 combines the intermediate beam bundles 22-1, 22-2, ... in the manner described in more detail below, so that they run in a common radiation direction 26 and form the output beam 12. The radiation powers of the input laser beams 16-1, 16-2, ... are combined in the output beam 12, and the output beam 12, like the input laser beams 16, is broadband (i.e., has a spectral bandwidth that encompasses all spectral bandwidths of the input laser beams 16).

[0042] The Figure 2 shows a sketched representation to explain an exemplary embodiment of the device 18. For reasons of clarity, Figure 2However, only one pre-compensation unit 20 is outlined as well as a combination unit 24 arranged downstream of the pre-compensation unit 20 in the beam path.

[0043] The precompensation unit 20 has a diffractive optic 28, which in the example shown comprises two diffractive optical elements (DOEs), namely a first diffractive optical element 30 and a second diffractive optical element 32 following in the beam path. The diffractive optical elements 30, 32 can be designed, for example, as diffraction gratings. In the example shown, both diffractive optical elements operate in reflection mode; in particular, they are reflection gratings.

[0044] The diffractive optical elements 30, 32 are each characterized by an associated angular dispersion w. The angular dispersion represents the change in a diffraction angle α or β for an input laser beam 16 as a function of its wavelength λ. Therefore, the angular dispersion of the first diffractive optical element 30 can be defined as w = dα / dλ. Accordingly, the angular dispersion of the second diffractive optical element 32 is defined as w = dβ / dλ.

[0045] The input laser beam 16 propagates along an irradiation direction 34 before impinging on the first diffractive optical element 30 and, in the example discussed, has a high beam quality M 2< (intrinsic, diffraction-related divergences are not considered in the present example, as explained above). The input laser beam 16 is broadband and comprises spectral components, of which Figure 2three wavelengths λ 1 , λ 2 , λ 3 are indicated as examples.

[0046] The input laser beam 16 strikes the first diffractive optical element 30 with its spectral components (wavelengths λ 1 , λ 2 , λ 3 ) along the incident direction 34. Due to the angular dispersion, the various spectral components with wavelengths (λ 1 , λ 2 , λ 3 ) are diffracted differently by the first diffractive optical element 30. By way of example, the first diffraction order, into which a large part of the radiation intensity is to be converted in the example shown, is considered below. With reference to the incident direction 34, the spectral components with wavelengths λ 1 , λ 2 , λ 3 are thus diffracted at different diffraction angles α(λ). The first diffractive optical element therefore converts the input laser beam 16 into a divergent beam bundle 36 by diffraction.In the divergent beam bundle 36, the spectral components with wavelengths (λ 1 , λ 2 , λ 3 ) no longer coincide in a single laser beam, but are spatially spread out. Spectral components with short wavelengths are located on one side of the divergent beam bundle 36, and spectral components with long wavelengths are located on the opposite side of the divergent beam bundle 36.

[0047] The first diffractive optical element 30 and the second diffractive optical element 32 are arranged with respect to one another and designed such that the spectral components with wavelengths λ 1 , λ 2 , λ 3 are detected by the second diffractive optical element 32. Due to the fanning out in the divergent beam 36, the various spectral components impinge on the second diffractive optical element 32 at different positions, on the one hand, and at different angles of incidence, on the other hand (for example, measured relative to a surface normal to a surface of the second diffractive optical element 32).

[0048] The second diffractive optical element 32 is now designed such that the various spectral components with wavelengths λ 1 , λ 2 , λ 3 , after diffraction at the second diffractive optical element 32, all run parallel to one another in a main direction 38. Thus, after diffraction at the second diffractive optical element 32, the spectral components form the intermediate beam 22, in which the various spectral components with wavelengths λ 1 , λ 2 , λ 3 are spatially spread apart and run parallel to one another. In the intermediate beam 22, the various spectral components, in the example shown, are sorted along an expansion direction 40 with increasing wavelength.

[0049] The parallel course of the various spectral components in the intermediate beam 22 can be achieved, for example, in that the angular dispersion dα / dλ of the first diffractive optical element 30 is the same as the angular dispersion dβ / dλ of the second diffractive optical element 32. The intermediate beam 22 then has, in particular along the expansion direction 40, a width which (in the range of small angles) is substantially proportional to the spectral bandwidth of the input laser beam 16.

[0050] In the example shown, the intermediate beam bundle 22 passes through an adaptation optics 42 in the beam path after the second diffractive optical element 32, which (only by way of example) can have one or more deflection mirrors 44 (e.g. plane mirrors) and / or one or more lens means 46 for shaping beam properties.

[0051] The intermediate beam bundle 22 is then detected by the combination unit 24. The combination unit 24 serves to combine the majority of the intermediate beam bundles 22 (cf. Figure 1 ) to form the common output beam 12. The combination unit 24 is tuned to the pre-compensation unit 20 in such a way that the expanded intermediate beam bundles 22 are not only combined with each other, but also the beam quality of the input laser beams is largely retained in the output beam 12. In the Figure 2 The functioning of the combination unit 24 is explained using only one intermediate beam bundle as an example.

[0052] The combination unit 24 in turn comprises a first diffractive optical element 48 and a second diffractive optical element 50 following in the beam path. Corresponding to the diffractive optical elements 30, 32 of the pre-compensation unit 20, the diffractive optical elements 48, 50 of the combination unit 24 are characterized by an angular dispersion. In the example shown, γ denotes the diffraction angle at the first diffractive optical element 48 and φ denotes the diffraction angle at the second diffractive optical element 50. Accordingly, the angular dispersions w = dγ / dλ and w = dδ / dλ are defined by the first diffractive optical element 48 and the second diffractive optical element 50, respectively.

[0053] The first diffractive optical element 48 of the combination unit 24 is designed such that the spectral components with the different wavelengths (λ 1 , λ 2 , λ 3 ) are converted by diffraction into a convergent beam 52, which forms a beam waist 54. Since the spectral components with wavelengths (λ 1 , λ 2 , λ 3 ) of the intermediate beam 22 impinge on the first diffractive optical element 48 at different positions, the desired convergent beam 52 can be achieved by appropriately adjusting the angular dispersion of the first diffractive optical element 48. In particular, the angular dispersion of the first diffractive optical element 48 can be selected to match the angular dispersions of the diffractive optical elements 30, 32 of the precompensation unit 20.

[0054] The second diffractive optical element 50 of the combination unit 24 is designed and positioned such that the beam waist 54 lies substantially on an effective surface of the second diffractive optical element 50. The second diffractive optical element 50 is then designed such that the spectral components (wavelengths λ 1 , λ 2 , λ 3 ) incident at different angles are all diffracted in the emission direction 26 and thus combined to form the output beam 12.

[0055] For example, this can again be achieved by selecting the angular dispersion of the second diffractive optical element to match the angular dispersions of the diffractive optical elements 30, 32 of the pre-compensation unit 30 and the angular dispersion of the first diffractive optical element 48 of the combination unit 24.

Claims

1. Device (18) for combining at least two input laser beams (16; 16-1, ..., 16-n), wherein the input laser beam (16) has a spectral bandwidth and accordingly comprises different spectral components having different wavelengths (λ1, λ2, λ3), the device comprising: - at least one pre-compensation unit (20) for the at least two input laser beams (16), wherein the pre-compensation unit (20) comprises at least one diffractive optical system (28) which expands the input laser beam (16) into an associated intermediate beam bundle (22) in which the spectral components run so as to be arranged spatially next to one another with increasing wavelength (λ1, λ2, λ3), wherein the pre-compensation unit (20) comprises at least a first diffractive optical element (30) and a second diffractive optical element (32) arranged downstream in the beam path; - a combination unit (24) for the at least two intermediate beam bundles (22), wherein the combination unit (24) comprises at least one further first diffractive optical element (48) and a further second diffractive optical element (50) arranged downstream in the beam path, and wherein the combination unit (24) is tuned to the pre-compensation unit (20) in such a way that the further first diffractive optical element (48) of the combination unit (24) transforms each intermediate beam bundle (20) into a convergent beam bundle (52) having a beam waist (54), wherein the beam waist (54) is on the further second diffractive element (50) of the combination unit (24), and wherein the further second diffractive optical element (50) of the combination unit (24) is designed in such a way that all incident spectral components are diffracted in a common radiation direction (26), characterized in that the diffractive optical elements (30, 32) of the pre-compensation unit (20) and the diffractive optical elements (48, 50) of the combination unit (24) have angular dispersions which differ from one another, and wherein the pre-compensation unit (20), which is downstream, in the beam path, of the second diffractive optical element (32) of the pre-compensation unit (20), and / or the combination unit (24), which is upstream, in the beam path, of the further first diffractive optical element (48) of the combination unit (24), comprises an adaptation optical system (42) for changing convergence properties and / or divergence properties and / or a beam width for the purpose of optically tuning the pre-compensation unit (20) to the combination unit (24).

2. Device (18) according to claim 1, wherein the pre-compensation unit (20) is designed in such a way that all spectral components in the intermediate beam bundle (22) run parallel to one another.

3. Device according to claim 1, wherein the first diffractive optical element (30) of the pre-compensation unit (20) is designed and arranged in such a way that the different spectral components of the input laser beam (16) are diffracted in different directions and, in the beam path between the first (30) and the second (32) diffractive optical element of the pre-compensation unit (20), form a divergent beam bundle (36).

4. Device (18) according to claim 3, wherein the second diffractive optical element (32) of the pre-compensation unit (20) is designed and arranged in such a way that the different spectral components of the divergent beam bundle (36) are all diffracted in the same direction.

5. Device (18) according to any of the preceding claims, wherein the pre-compensation unit (20) is designed in such a way that the intermediate beam bundle (22) has a spatial width which is greater, the greater the bandwidth of the input laser beam (16) is.

6. Device (18) according to any of claims 1 - 5, wherein the first diffractive optical element (30) and the second diffractive optical element (32) of the pre-compensation unit (20) have matching angular dispersion (w).

7. Device (18) according to any of claims 1 - 6, wherein the first diffractive optical element (30) and the second diffractive optical element (32) of the pre-compensation unit (20) are designed as reflection grating or as transmission grating.

8. Device (18) according to claim 7, wherein the first diffractive optical element (30) and the second diffractive optical element (32) of the pre-compensation unit (20) are characterized by matching grating constants.

9. Device (18) according to any of claims 1 - 8, wherein the first diffractive optical element (30) and the second diffractive optical element (32) of the pre-compensation unit (20) are designed and arranged in such a way that, upon diffraction of the input laser beam (16) at the first diffractive optical element (30) of the pre-compensation unit (20), a first diffraction order of the spectral components of the input laser beam (16) is detected by the second diffractive optical element (32) of the pre-compensation unit (20).

10. Device (18) according to any of claims 1 - 9, wherein the adaptation optical system (42) comprises at least one, in particular planar, deflecting mirror (44).

11. Device (18) according to any of claims 1 - 10, wherein the adaptation optical system (42) comprises at least one telescope having at least two lens means (46).

12. Device (18) according to any of the preceding claims, comprising a plurality of pre-compensation units (20-1, ..., 20-n), each having a diffractive (28) optical system, wherein each input laser beam (16-1, ... 16-n) is assigned a pre-compensation unit (20-1, ..., 20-n).

13. Device (18) according to claim 12, wherein the plurality of pre-compensation units (20-1, ..., 20-n) are arranged in such a way that the intermediate beam bundles (22-1 , ..., 22-n) created by the different pre-compensation units (20-1, ..., 20-n) run parallel to one another.