DEVICE FOR COMBINING AT LEAST TWO LASER BEAMS

Abstract

A device for combining at least two input laser beams having different spectral components. At least one pre-compensation unit for the at least two input laser beams has a diffractive optical unit which expands the input laser beam into an intermediate beam bundle in which the spectral components are spatially arranged so as to be adjacent to one another with increasing wavelength. A combination unit has at least a first diffractive optical element and a second diffractive optical element, the combination unit being aligned with the pre-compensation unit in such a way that the first diffractive optical element converts an intermediate beam bundle into a convergent beam bundle having a beam waist, the beam waist lying on the second diffractive element, and the second diffractive optical element being designed in this way that all incident spectral components are diffracted in a common radiation direction.

Claims

1. A device for combining at least two input laser beams, the input laser beam having a spectral bandwidth and comprises different spectral components each with different wavelengths, the device comprising: at least one pre-compensation unit for the at least two input laser beams, wherein the pre-compensation unit has at least one diffractive optic which expands the input laser beam into a respectively assigned intermediate beam bundle in which the spectral components are spatially arranged so as to be adjacent to one another with increasing wavelength; a combination unit for the at least two intermediate beam bundles, the combination unit comprising at least a first diffractive optical element and a second diffractive optical element arranged downstream in the beam path, and the combination unit being aligned with the pre-compensation unit such that the first diffractive optical element converts an intermediate beam bundle into a convergent beam bundle having a beam waist, the beam waist lying on the second diffractive element, and the second diffractive optical element being designed such that all incident spectral components are diffracted in a common radiation direction.

2. The device according to claim 1, wherein the pre-compensation unit is designed such that all spectral components in the intermediate beam run parallel to one another.

3. The device according to claim 1, wherein the pre-compensation unit has at least one first diffractive optical element and has, downstream in the beam path, a second diffractive optical element.

4. The device according to claim 3, wherein the first diffractive optical element of the pre-compensation unit is designed and arranged such that the different spectral components of the input laser beam are bent in different directions and in the beam path between the first and the second diffractive optical element form a divergent beam bundle.

5. The device according to claim 4, wherein the second diffractive optical element of the pre-compensation unit is designed and arranged such that the different spectral components of the divergent beam bundle are all diffracted in the same direction.

6. The device according to claim 1, wherein the pre-compensation unit is designed such that the intermediate beam bundle has a spatial width which is greater, the greater the bandwidth of the input laser beam.

7. The device according to claim 3, wherein the first diffractive optical element and the second diffractive optical element of the pre-compensation unit have a corresponding angular dispersion.

8. The device according to claim 3, wherein the first diffractive optical element and the second diffractive optical element are designed as reflection grids or as transmission grids.

9. The device according to claim 8, wherein the first diffractive optical element and the second diffractive optical element are characterized by matching grid constants.

10. The device according to claim 3, wherein the first diffractive optical element and the second diffractive optical element are designed and arranged such that upon diffraction of the input laser beam at the first diffractive optical element a first diffraction order of the spectral components of the input laser beam is detected by the second diffractive optical element.

11. The device according to claim 3, wherein the diffractive optical elements of the pre-compensation unit and the diffractive optical elements of the combination unit have a corresponding angular dispersion.

12. The device according to claim 3, wherein the diffractive optical elements of the pre-compensation unit and the diffractive optical elements of the combination unit have angular dispersions that differ from one another, and wherein the pre-compensation unit and/or the combination unit comprise adaptation optics for changing convergence properties and/or divergence properties and/or a beam width.

13. The device according to claim 12, wherein the adaptation optics has at least one, in particular planar, deflecting mirror.

14. The device according to claim 12, wherein the adaptation optics has at least one telescope with at least two lenses.

15. The device according to claim 1, further comprising a plurality of pre-compensation units each having a diffractive optics, wherein each input laser beam has a pre-compensation unit.

16. The device according to claim 15, wherein the plurality of pre-compensation units are arranged such that the intermediate beam bundles created by the different pre-compensation units run parallel to each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0034] FIG. 1 is a sketched representation of a device for combining a plurality of broadband input laser beams, comprising pre-compensation units (sketched representation) and a combination unit (sketched representation); and

[0035] FIG. 2 is a sketched representation of a device with a pre-compensation unit and a combination unit.

DETAILED DESCRIPTION

[0036] FIG. 1 shows a device, denoted in its entirety by reference numeral 10, for generating a particularly high-energy laser beam (output beam 12) in a sketched illustration. The device 10 comprises a plurality n of input laser sources 14-1, 14-2, . . . 14-n−1, 14-n, which each emit an input laser beam 16-1, 16-2, . . . .

[0037] Each input laser beam 16-1, 16-2, . . . has a certain spectral bandwidth and in this respect comprises different spectral components having different wavelengths A. The device 10 serves in particular for the purpose of providing a high-energy output beam 12 with a beam quality M.sup.2 that is as similar as possible to or corresponding to the beam quality M.sup.2 of the individual input laser sources 14-1, 14-2, . . . . The input laser sources 14 can be designed as fiber lasers, for example, which are operated in their basic mode in particular for radiation 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 a beam broadening when propagating over longer distances. For the purpose of explaining the present invention, however, this effect will be neglected in the present description.

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

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

[0040] As will be explained in detail below, each pre-compensation unit 20-1, 20-2, . . . transforms the detected input laser beam 16-1, 16-2, . . . into a respectively assigned, broadened intermediate beam bundle 22-1, 22-2, . . . . In the intermediate beam bundle 22, the spectral components of the respectively assigned input laser beam 16 are no longer superimposed in a common beam, but rather spatially arranged so as to be adjacent to one another with increasing wavelength (see below).

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

[0042] FIG. 2 shows a sketched illustration to explain an example of the device 18. For the sake of clarity, however, only one pre-compensation unit 20 is sketched in FIG. 2 as well as a combination unit 24 arranged downstream of the pre-compensation unit 20 in the beam path.

[0043] The pre-compensation unit 20 has a diffractive optics 28, which in the example shown comprises two diffractive optical elements (DOE), 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 as diffraction grids, for example. In the example shown, both diffractive optical elements act in reflection, in particular reflection grids are involved.

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

[0045] Before it hits the first diffractive optical element 30, the input laser beam 16 propagates along an irradiation direction 34 and, in the example discussed, has a high beam quality M.sup.2 (intrinsic, diffraction-related divergences are not taken into account in the present example, as explained above). The input laser beam 16 is broadband and comprises spectral components, of which three wavelengths λ.sub.1, λ.sub.2, λ.sub.3 are indicated in FIG. 2 by way of example.

[0046] The input laser beam 16 hits the first diffractive optical element 30 with its spectral components (wavelengths λ.sub.1, λ.sub.2, λ.sub.3) along the irradiation direction 34. Due to the angular dispersion, the different spectral components with wavelengths (λ.sub.1, λ.sub.2, λ.sub.3) are diffracted differently at the first diffractive optical element 30. In the following, the first order of diffraction is considered as an example, into which a large part of the radiation intensity is supposed to pass in the example shown. With respect to the irradiation direction 34, the spectral components with wavelengths λ.sub.1, λ.sub.2, λ.sub.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 means of diffraction. In the divergent beam bundle 36, the spectral components with the wavelengths (λ.sub.1, λ.sub.2, λ.sub.3) therefore no longer coincide in a single laser beam, but are spatially fanned out. Spectral components with a small wavelength lie on one side of the divergent beam 36 and spectral components with a large wavelength lie on the opposite side of the divergent beam 36.

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

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

[0049] The parallel course of the various spectral components in the intermediate beam bundle 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 bundle 22 then has, in particular along the expansion direction 40, a width which (in the region of small angles) is essentially 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 deflecting mirrors 44 (e.g. plane mirrors) and/or one or more lenses 46 for shaping beam properties.

[0051] The intermediate beam 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. FIG. 1) to form the common output beam 12. The combination unit 24 is coordinated with the pre-compensation unit 20 in such a way that the expanded intermediate beam bundles 22 are not only combined with one another, but the beam quality of the input laser beams is largely retained in the output beam 12. In FIG. 2, the mode of operation of the combination unit 24 is explained using only one intermediate beam 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 designates the diffraction angle on the first diffractive optical element 48 and φ the diffraction angle on the second diffractive optical element 50. Correspondingly, 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.sub.1, λ.sub.2, λ.sub.3) are converted into a convergent beam bundle 52 by diffraction, which forms a beam waist 54. Since the spectral components with wavelengths (λ.sub.1, λ.sub.2, λ.sub.3) of the intermediate beam bundle 22 hit the first diffractive optical element 48 at different positions, the desired convergent beam bundle 52 can be achieved by suitable alignment of the angular dispersion of the first diffractive optical element 48. In particular, for this purpose 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 pre-compensation unit 20.

[0054] The second diffractive optical element 50 of the combination unit 24 is designed and positioned in such a way 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.sub.1, λ.sub.2, λ.sub.3) incident at different angles are all diffracted in the radiation direction 26 and are thus combined to form the output beam 12.

[0055] For example, this can in turn be achieved in that the angular dispersion of the second diffractive optical element is selected 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.

[0056] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims