阅读说明：本技术 泵浦激光辐射的均匀化 (Homogenization of pump laser radiation ) 是由 S·多雷尔 S·里德 C·蒂尔科恩 于 2018-04-23 设计创作，主要内容包括：一种用于产生均匀化的泵浦激光束(15B)的泵浦单元(2),所述泵浦单元用于激光系统(1)的激光活性介质(13)的光学泵浦,所述泵浦单元包括泵浦激光系统(3),其中多个激光束(19A,19B,19C,19A’,19B’,19C’)叠加成主泵浦激光束(15A)。所述泵浦单元(2)还包括用于使所述主泵浦激光束(15A)均匀化的光学射束成形系统(5),其中,所述光学射束成形系统(5)具有微透镜装置(7)和光学的光混合元件(9),所述微透镜装置具有多个透镜(7A),所述光学的光混合元件用于通过多次反射来引导所述主泵浦激光束(15A)并且用于输出所述均匀化的泵浦激光束(15B)。所述微透镜装置(7)如此布置,使得所述主泵浦将光束(15A)在耦合到所述光学的光混合元件(9)中前辐射穿过所述微透镜装置(7)的多个透镜(7A)。(A pump unit (2) for generating a homogenized pump laser beam (15B) for optical pumping of a laser active medium (13) of a laser system (1), comprising a pump laser system (3), wherein a plurality of laser beams (19A, 19B, 19C, 19A ', 19B ', 19C ') are superimposed into a main pump laser beam (15A). The pump unit (2) further comprises an optical beam shaping system (5) for homogenizing the primary pump laser beam (15A), wherein the optical beam shaping system (5) has a microlens arrangement (7) with a plurality of lenses (7A) and an optical light mixing element (9) for guiding the primary pump laser beam (15A) by multiple reflections and for outputting the homogenized pump laser beam (15B). The microlens arrangement (7) is arranged in such a way that the primary pump radiates a light beam (15A) through a plurality of lenses (7A) of the microlens arrangement (7) before being coupled into the optical light-mixing element (9).)

1. A pump unit (2) for generating a homogenized pump laser beam (15B) for optical pumping of a laser-active medium (13) of a laser system (1), having:

A pump laser system (3), wherein a plurality of laser beams (19A, 19B, 19C, 19A ', 19B ', 19C ') are superimposed into a main pump laser beam (15A);

An optical beam shaping system (5) for homogenizing the primary pump laser beam (15A), wherein the optical beam shaping system (5) has a microlens arrangement (7) with a plurality of lenses (7A) and an optical light mixing element (9) for directing the primary pump laser beam (15A) by multiple reflections and for outputting the homogenized pump laser beam (15B);

Wherein the microlens arrangement (7) is arranged in such a way that the primary pump laser beam (15A) is radiated through a plurality of lenses (7A) of the microlens arrangement (7) before being coupled into the optical light-mixing element (9).

2. The pumping unit (2) of claim 1, wherein the pump laser system (3) has a plurality of pump modules (3A, 3B, 3C), each pump module (3A, 3B, 3C) emitting a plurality of laser beams (19A, 19B, 19C, 19A ', 19B', 19C '), and the main pump laser beam (15A) is generated by superposition of the laser beams (19A, 19B, 19C, 19A', 19B ', 19C') of the pump modules (3A, 3B, 3C).

3. Pump unit (2) according to one of the preceding claims, wherein the position of the microlens arrangement (7) in the beam path between the pump laser system (3) and the optical light mixing element (9) and the lateral offset of adjacent lenses (7A) of the microlens arrangement (7) are selected such that at least five lenses (7A) of the microlens arrangement (7) are illuminated.

4. Pump unit (2) according to any of the preceding claims, wherein the light mixing element (9) has an entrance face (29A) and an exit face (29B), and the microlens arrangement (7) is arranged directly on the entrance face of the optical light mixing element (9) or in the vicinity of the entrance face of the optical light mixing element (9).

5. Pump unit (2) according to claim 4, wherein the lenses (7A) of the microlens arrangement (7) are arranged with the following misalignment between two lenses (7A) in the arrangement direction: the offset corresponds at most to one fifth of the dimension of the entry surface (29A) in the alignment direction.

6. Pump unit (2) according to any of the preceding claims, wherein the micro lens arrangement (7) is an array of cylindrical lenses.

7. Pump unit (2) according to any of the preceding claims, wherein the microlens arrangement (7) is arranged in an opening of a beam stop element (28).

8. pump unit (2) according to any of the preceding claims, wherein the microlens arrangement (7) is a biconvex microlens arrangement of telecentric design.

9. Pump unit (2) according to any of the preceding claims, wherein the light mixing element (9) is configured as a light mixer rod as follows: the light beams are guided from an entry surface (29A) of the light mixer rod to an exit surface (29B) of the light mixer rod by means of a completely internal multiple reflection, and the number of reflections of the light beams in the light mixer rod depends on the angle of incidence of the respective light beam on the entry surface (29A), so that a homogenized distribution of the emitted light beams is present on the exit surface (29B).

10. Pump unit (2) according to any of the preceding claims, wherein the pump laser system (3) is configured to be assembled with a different number of pump modules (3A, 3B, 3C) and the length of the light mixing element (9) and the number of lenses (7A) radiated through are designed such that the intensity fluctuation in the homogenized pump laser beam (15B) is below 15% with a set minimum number of pump modules (3A, 3B, 3C) used in combination with the microlens arrangement (7).

11. Pump unit (2) according to any of the preceding claims, wherein the numerical aperture of the microlens arrangement (7) is matched to the divergence of the main pump beam (15A).

12. Pump unit (2) according to one of the preceding claims, further having focusing optics (27) for generating a converging beam profile for coupling the primary pump laser beam (15A) into the light-mixing element (9);

Wherein the microlens arrangement (7) is arranged in the region of the at least substantially superimposed laser beams (19A, 19B, 19C, 19A ', 19B ', 19C ') of the pump laser system (3) in the converging beam profile between the focusing optics (27) and the light mixing element (9).

13. The pumping unit (2) according to any of the preceding claims, wherein the pump laser system (3) comprises a plurality of laser diode-based pumping modules (3A, 3B, 3C), and one laser beam region (25A, 25B, 25C) is assigned to each of the plurality of pumping modules (3A, 3B, 3C), wherein adjacent laser beam regions (25A, 25B, 25C) are arranged in the main pump laser beam (15A) in the direction of the fast axis alongside one another before superposition.

14. The pumping unit (2) of claim 13, wherein the laser diode based pumping modules (3A, 3B, 3C) are arranged side by side to each other in the direction of the fast axis, such that the laser radiation of adjacent pumping modules (3A, 3B, 3C) form adjacent regions of the main pumping laser beam (15A) before superposition; or

The laser radiation of the pump modules (3A, 3B, 3C) is guided in such a way that adjacent laser beam regions (25A, 25B, 25C) of the main pump laser beam (15A) are generated by the respectively associated pump modules (3A, 3B, 3C) and are aligned next to one another by means of optics.

15. The pump unit (2) of any of claims 1 to 12, wherein the pump laser system (3) comprises a plurality of laser diode-based pump modules (3A, 3B, 3C) each having a plurality of diode bars for emitting the laser beams (19A, 19B, 19C, 19A ', 19B', 19C '), wherein in the main pump laser beam (15A) the laser beams (19A, 19B, 19C, 19A', 19B ', 19C') of the diode bars of one pump module (3A, 3B, 3C) are arranged spaced apart from each other in the fast axis direction of the diode bars and are interleaved with each other with respect to a plurality of pump modules (3A, 3B, 3C).

16. The pump unit (2) according to claim 15, further having optical means for interleaving the laser radiation of different pump modules (3A, 3B, 3C) such that the laser radiation of the diode bars of different pump modules (3A, 3B, 3C) form, before superposition, mutually side-by-side fractions of the main pump laser beam (15A).

17. Pump unit (2) according to any of claims 13 to 16, wherein the micro-lens arrangement (7) is configured as an array of cylindrical lenses and the cylindrical lenses are directed in the direction of the fast axis for focusing.

18. Laser system (1), in particular laser amplifier system, having:

the pump unit (2) according to any of claims 1 to 17;

A laser cavity (11) having a laser active medium (13) to be pumped, through which a homogenized pump laser beam (15B) generated by the pumping unit (2) is radiated at least once.

19. Laser system (1) according to claim 18, wherein the homogenized pump laser beams (15B) are rotated between passing through the laser active medium (13) one after the other.

Technical Field

The invention relates to an optical system for uniformly superimposing laser radiation, in particular for superimposing pump laser radiation (pumplastrahlung) of a plurality of laser diode modules, which are used, for example, in a pump laser system. The invention also relates to a laser system, in particular pumped by means of a diode laser, for amplifying continuous laser radiation (cw-Laserstrahlung) and pulsed laser radiation to high powers and/or high pulsed energies.

background

Laser systems (e.g. high power solid state lasers) require coupling in of a correspondingly designed pump power into the amplification-based medium. In order to achieve a high pump power, the laser radiation of a plurality of pump lasers can be superimposed to form a pump laser beam. Furthermore, the superimposed laser radiation from the plurality of laser diodes may pass through the crystal multiple times in a folded configuration, for example a disk-shaped amplifying medium of a disk laser amplifier. The pump laser system may be based on high power diode laser modules each having a plurality of laser diode bars (Laserdiodebarren).

The combination of the laser radiation of a plurality of laser diodes can be carried out, for example, by means of interleaving as described in EP 2342596B 1And (5) realizing. The pump modules have diode bars arranged opposite one another, so that the output radiation of such a pump module has beam-free regions between the laser radiation emitted by the diode bars. By interleaving a plurality of pump modules, the beamless regions of the pump modules are filled by the remaining pump modules.

In the case of diode bars of compact construction, the beam-free region is reduced, so that, for example, if the pump modules are arranged directly opposite one another, the output radiation of the pump modules can be combined in a subsequent common beam path to form a pump laser beam.

The output radiation of the different pump modules, i.e. the different laser bars (Laserbarren), can be mixed in an optical mixer before the pump laser beams are coupled into the laser-active medium, as a result of which a more uniform output beam profile of the homogenized (homogeniesen) pump laser beams can be produced after the optical mixer. An exemplary laser pumping device with a beam homogenizing device with an optical homogenizer for homogenizing a portion of the pump radiation is disclosed in WO 2010/052308a 1.

In order to provide scalability of the pump power of the pump laser system, the number of pump modules used in an otherwise identical pump laser system may vary depending on the application. However, if the number of pump modules is reduced, the angular range of the pump laser beam coupled into the optical mixer may be reduced, so that homogenization of the pump laser beam cannot be completely achieved or sufficient homogenization of the pump laser beam for the application cannot be achieved. This may result in an increased sensitivity of the pumped laser system (e.g. laser amplification system) to the alignment of the pumped laser beam. For example, increased sensitivity to changes in the light path and/or intensity distribution occurs. The improved sensitivity can be attributed in particular to the following: when, for example, one pump module is exchanged for another, the power distribution in the pump beam changes, wherein the new pump module usually has slightly different beam characteristics, in particular a slightly different beam angle distribution. The homogenization performed in the light mixer may be insufficient if, for example, the usually large angular range of the focused pump light is not filled by the laser beam. In this way, different power distributions may be obtained for different pump modules, which are respectively different and insufficient and thus lead to instability of the system or to a necessary recalibration of the system. For example, in the case of the disk laser system mentioned, the power distribution in the amplification medium in the individual channels plays a decisive role for the resonator stability and also for the start-up behavior (Einlaufverhalten) or the step response of the disk laser system.

Disclosure of Invention

One aspect of the invention is based on the following tasks: a pump unit for generating a homogenized pump laser beam is proposed, which is designed in particular for applications with a different number of pump modules. In this case, an optical beam shaping system for beam homogenization should achieve improved homogenization, in particular with a low number of pump modules. In other words, a sufficient homogenization should be achieved even in the presence of beam-free regions in the pump beam to be homogenized. Another aspect of the invention is based on the following tasks: the stability of the pump laser system and accordingly of the pumped laser system (in particular of the laser amplification system) is increased and the replacement of the pump modules is simplified.

At least one of these objects is achieved by a pump unit for generating a homogenized pump beam according to claim 1 and by a laser system according to claim 18. Further developments are specified in the dependent claims.

In one aspect, a pump unit for generating a homogenized pump laser beam has a pump laser system and an optical beam shaping system for optically pumping a laser-active medium of the laser system. In the case of a pump laser system, a plurality of laser beams are superimposed into a main pump laser beam. The optical beam shaping system serves for homogenizing the primary pump laser beam, wherein the optical beam shaping system has a microlens arrangement with a plurality of lenses and an optical light-mixing element for directing the primary pump laser beam by multiple reflections and for outputting the homogenized pump laser beam. The microlens arrangement is arranged in such a way that the main pump laser beam radiates through the lenses of the (durchtrahlen) microlens arrangement before being coupled into the optical light-mixing element.

On the other hand, a laser system, in particular a laser amplifier system, comprises such a pumping unit and a laser cavity with a laser-active medium to be pumped, through which laser-active medium the homogenized pumping laser beam generated by the pumping unit is radiated at least once.

In an exemplary embodiment, the pump laser system comprises a plurality of pump modules, wherein each pump module emits a plurality of laser beams and generates a main pump laser beam by superimposing the laser beams of the pump modules.

In an exemplary embodiment, the position of the microlens arrangement in the beam path between the pump laser system and the optical light mixing element and the lateral offset of the adjacent lenses of the microlens arrangement are selected such that at least five lenses of the microlens arrangement are illuminated. The light-mixing element has, for example, an entrance face and an exit face, and the microlens arrangement is arranged directly on or in the vicinity of the entrance face of the optical light-mixing element. Furthermore, the microlens arrangement may be arranged in an opening of a beam stop element (strahlblediencemement). In an exemplary embodiment, the lenses of the microlens arrangement can be aligned in the alignment direction (Aufreihungsrichtung) with a misalignment between the two lenses which corresponds at most to one fifth of the dimension of the entry face of the optical light-mixing element in the alignment direction.

In an exemplary embodiment, the light mixing element is configured as a light mixer rod (lichtmsercherstab) as follows: the light beam is guided by a completely internal multiple reflection from the entrance surface of the light mixer rod via the light mixer rod to the exit surface of the light mixer rod, and the number of reflections of the light beam in the light mixer rod depends on the angle of incidence of the respective light beam on the entrance surface, so that a homogenized distribution of the emitted light beam is present on the exit surface.

In an exemplary embodiment, the pump laser system is configured to be assembled with a different number of pump modules, and the length of the light mixing element and the number of lenses radiated through are designed such that the intensity fluctuation in the homogenized pump laser beam is less than 15% with the minimum number of pump modules provided in combination with the microlens arrangement.

in general, the numerical aperture of the microlens assembly can be matched to the divergence of the main pump beam.

In some exemplary embodiments, the pump unit may also have a focusing optic for generating a converging beam profile for coupling the main pump beam into the light-mixing element, wherein the microlens arrangement is arranged in the region of the at least substantially superimposed laser beams of the pump laser system in the converging beam profile between the focusing optic and the light-mixing element.

In some exemplary embodiments, the pump laser system may include a plurality of laser diode-based pump modules. One of the pump modules can then each be assigned a laser beam region, wherein adjacent (in particular planar closed) laser beam regions of the main pump laser beam are arranged next to one another in the direction of the fast axis before the superposition. The laser diode-based pump modules can be arranged next to one another in the direction of the fast axis, so that the laser beams of adjacent pump modules form adjacent regions of the main pump laser beam before superposition. Alternatively, the laser radiation of the pump modules may be directed in such a way that adjacent laser radiation regions of the main pump laser beam are generated by the respectively associated pump modules and are aligned next to one another by means of optics.

In some exemplary embodiments, the pump laser system may include a plurality of laser diode-based pump modules each having a plurality of diode bars for emitting laser beams, wherein, in the main laser beam, the laser beams of the diode bars of one pump module are arranged spaced apart from each other in a fast axis direction of the diode bars and are interleaved with each other with respect to the plurality of pump modules. The pump unit can therefore also have lasers for different pump modulesAn optical device for interleaving the radiation, so that the laser radiation of the diode bars of different pump modules forms the mutually side-by-side share of the main pump laser beam before superposition

In an exemplary embodiment, the microlens assembly is configured as an array of cylindrical lenses, and the cylindrical lenses are oriented in the direction of the fast axis for focusing.

Furthermore, the embodiments disclosed herein may also improve the start-up characteristics of the disc laser system, and thus enable stable and efficient operation of the disc laser system. Furthermore, the microlens arrangement (microlens array) in front of the light mixing element enables an improved homogenization independent of the angular space.

Drawings

herein, a design is disclosed that achieves at least a partial improvement over the prior art. Further features and their suitability for the purpose emerge in particular from the following description of an embodiment with reference to the attached drawings. The figures show:

FIG. 1 shows a schematic diagram of an exemplary laser amplifier system with an optical beam shaping system for beam homogenization;

Fig. 2A to 2C show schematic diagrams of beam profiles (pump spots) with improved homogenization by means of a microlens arrangement;

Fig. 3A to 3C show schematic diagrams of beam profiles (pump spots) without homogenization using a microlens arrangement.

Detailed Description

The aspects described herein are based, in part, on the following recognition: the microlens arrangement (also referred to herein as a microlens array) makes it possible to configure the angular distribution of the pump laser beams introduced into the light mixing element independently of the number of pump modules used for the angular distribution, which achieves improved homogenization. The homogenization by the microlens arrangement is generally more independent of the main pump laser beam. The inventors have recognized, in particular, that the optical beam shaping system for homogenizing the pump laser beam is designed in such a way that a sufficient homogenization should be able to be achieved independently of the number of laser radiation fractions used. Especially in the case of an arrangement of the output beams of the pump modules located next to or opposite one another, a large area in the beam profile of the main pump laser beam in the vicinity of the pump modules can remain beam-free, if fewer pump modules are used than are required for a complete irradiation of the beam profile. It is known that, despite a lack of coverage of the cross section of the main pump laser beam, the combination of a microlens arrangement (for example an array of cylindrical lenses) with a light-mixing element before the superposition of the laser radiation fractions of the pump modules still enables sufficient beam homogenization.

The optical beam shaping system of the pump unit proposed here can be used advantageously, in particular, in the case of a vertical stacking of the laser radiation fractions, not on the basis of an interleaving of the laser radiation of the respective laser bars, but on the basis of an optical or structural stacking of the laser radiation fractions of a plurality of laser bars of a pump module or of the output beams of a plurality of pump modules. As a result, a Stack of laser radiation fractions ("Stack") is usually produced in the fast axis direction in both cases.

This compact arrangement of the laser stripes enables a simple coupling-in optical system of the radiation emitted from the vertical stack in the (e.g. almost rotationally symmetric) optical mixing element, while approximately maintaining the brightness of the pump radiation. By the combination with the microlens arrangement proposed here, the beam shaping system can also be used in the following cases: the vertical stacking of the pump modules does not provide a laser radiation contribution over the entire beam cross-section before the superposition of the main pump laser beams, since the microlens arrangement produces a sufficient distribution of the angular measurement values of the laser beams which form the input beam in front of the optical mixing element.

The pump beam shaping and amplification processes and the associated components of an exemplary laser system 1 of the design disclosed here with an optical beam shaping system are explained below with reference to fig. 1 and 2. Fig. 3 comparatively shows the beam progression without a corresponding structure of the microlens arrangement.

The laser system 1 comprises a pump unit 2 with a pump laser system 3 having a plurality of pump modules 3A, 3B, 3C and an optical beam shaping system 5. The optical beam shaping system 5 further has a microlens arrangement 7 and a light mixing element 9. The laser system 1 further comprises an amplifier unit 11 (typically a laser cavity) with a laser active medium 13. In general, the pump laser system 3 generates a main pump laser beam 15A which is adapted to the respective desired pumping process of the laser-active medium 13 by means of the optical beam shaping system 5. Other features of the respective units are set forth in detail below.

The pump modules 3A, 3B, 3C can be designed, for example, as laser diode modules. In general, diode laser radiation allows an efficient pumping of the laser-active medium 13, wherein the main pump laser beam 15A is formed by a superposition of the diode laser radiation of a plurality of laser diode modules (typically the laser radiation of a plurality of pump modules). Fig. 1 shows, for example, three pump modules 3A, 3B, 3C, which are arranged schematically next to one another.

the pump module, which is designed as a laser diode module, comprises a plurality of laser bars, wherein each laser bar has a plurality of emitter regions. The laser bars of the pump modules may, for example, form a structural stack in which the emitter regions of the laser bars are arranged in the direction of the fast axis substantially without a misalignment in the slow axis, so that the output radiation of the laser bars of the pump modules is stacked in the direction of the fast axis. Alternatively, the emitter regions of the laser stripes in the pump modules can be arranged with a misalignment in the slow axis, wherein the following can then likewise be achieved by an optical stack with, for example, deflection mirrors and/or prisms: the output radiation of the laser bars of the pump modules are stacked in the direction of the fast axis (optical stack).

In older pump module architectures, the laser bars are spaced apart from one another in such a way that the interleaving of the laser radiation of the pump modules mentioned at the outset serves, for example, for generating a main pump laser beam. The dimensions of the individual laser bars are reduced in the case of modern pump module architectures such that the dimensions of the individual pump modules in the direction of the fast axis can be reduced to a few millimeters, which now make it possible for a plurality of pump modules to be arranged close to one another, for example directly next to one another in the direction of the fast axis. Interleaving can thus be dispensed with when generating the main pump laser beam, wherein a main pump laser beam having, for example, a substantially rectangular cross section can be generated despite the spatial proximity of the laser bars and the pump modules.

In general, the diode laser radiation of a plurality of laser diode modules is assembled in such a way that a main pump laser beam with a rectangular cross section is obtained. This may be deformed, for example, into a uniform circular pump spot or, in general, into a uniform circular excitation of the laser-active medium 13. Such beam deformation is furthermore realized in particular by means of the light-mixing element 9. Thus, for example, pump modules designed as the previously mentioned optical and/or structural stacks can be arranged in an array in the direction of the fast axis, so that the desired beam cross section of the main pump laser beam results. Alternatively, such pump modules can be arranged arbitrarily, and the associated diode radiations of different pump modules can be optically concentrated alongside one another to form a main pump laser beam.

Fig. 1 schematically shows an exemplary beam cross section of a main pump laser beam 15A for different embodiments of the pump laser system 3.

The beam cross sections 17A, 17B thus relate to the example of interleaving of the laser radiation of a plurality of pump modules mentioned at the outset, both in the case of a complete assembly of three pump modules (beam cross section 17A) and in the case of a partial assembly of two pump modules (beam cross section 17B).

In the beam cross section 17A of the main pump laser beam 15A, three groups of laser beams 19A, 19B, 19C can be seen, which are each associated with one of the three pump modules 3A, 3B, 3C. Each of the laser beams 19A, 19B, 19C originates from a laser bar, wherein a group of laser beams is emitted at a certain distance from each other due to the pump module structure. The elliptical shape of the beam profile of the laser beams 19A, 19B, 19C results from the different optical properties of the fast and slow axes of the diode laser beam generating device. Thus, the laser light of a single emitting area of the laser stripe diverges more in the fast axis direction than in the slow axis direction, which is known to be due to the laser process and the geometry of the emitting area.

By means of a mirror arrangement as described, for example, in EP 2342596B 1 mentioned at the outset, the laser beams 19A, 19B, 19C can be interlaced with one another in such a way that, despite the elliptical beam profile of each laser stripe, a substantially rectangular, in particular substantially square, intensity distribution is produced in cross section. This is illustrated, for example, in the beam cross section 17A corresponding to the complete assembly.

Superposition of the beams by interleaving is particularly common when the spacing of the laser stripes of the pump modules is in the range of a few millimeters.

The pumping of the laser-active medium 9 with such a main pump laser beam 15A produced by interleaving is a particular challenge for homogenization in the case of an incomplete assembly of the pump modules. In the case of an incomplete assembly of the pump modules, for example, the laser beam 19C is omitted, so that a beam-free region 21 is formed in the square beam cross section 17B. Without the use of a microlens arrangement, this beam-free region 21 can reduce the angular distribution of the coupling-in into the light-mixing element 9 in such a way that, in the case of an incomplete assembly, homogenization in the light-mixing device can lead to an inhomogeneous pump beam profile (in particular in the laser-active medium 13).

Fig. 1 shows exemplary beam cross sections 23A, 23B for the case of a compact pump module architecture. In the case of an arrangement of pump modules, which is designed, for example, as a structural stack or as an optical stack, each pump module can be assigned one laser beam region 25A, 25B, 25C of the main pump laser beam 15A. Each laser beam region 25A, 25B, 25C comprises a plurality of laser beams 19A ', 19B ', 19C ' having an elliptical beam profile, which are generated by respective diode bars of the pumping module. The beam cross section 23A corresponds to the complete assembly, i.e. the cross section of the main pump laser beam 15A which is completely irradiated before the superimposition.

As explained in beam cross section 23B, one or more beam-free regions 21 can also be present in this pump module configuration in the case of an incomplete assembly. Accordingly, in the case of this embodiment of the pump laser system 3, the reduced angular distribution is coupled into the light-mixing element 9 without the use of a microlens arrangement.

The laser beams 19A ', 19B ', 19C ' of the laser beam regions 25A, 25B, 25C or the interleaved laser beams 19A, 19B, 19C are superimposed, for example, with a (deflection) mirror and telescope arrangement for coupling into the light-mixing element 9.

The effect of the microlens arrangement 7 on homogenization is described below in connection with fig. 2 and 3. First, the other components of the optical beam shaping system 5 and the other components of the amplifier unit 11 are described.

In fig. 1, a lens 27 is shown which focuses the main pump laser beam 15A into the light mixing element 9, which lens represents a focusing optics typically comprising a plurality of optical elements. In the embodiment shown, the microlens arrangement 7 (with the schematically illustrated lens 7A) arranged in front of the light mixing element 9, for example, enables a slight beam expansion of the main pump laser beam 15A in the direction of the fast axis (here, for example, in the marking plane). However, other types of lenses 7A in the microlens arrangement 7 (e.g. in a lens array for focusing or for expansion) may also generally lead to an improved homogenization.

If the microlens array 7 is arranged directly on the entry face of the optical light-mixing element 9 or in the vicinity of the entry face of the optical light-mixing element 9 (see the microlens elements 7 'on the light-mixing element 9, which are shown by dashed lines in fig. 1), the respective lenses have the following dimensions, for example, in the direction of alignment of the laser beams 19A, 19B, 19C or in the direction of alignment of the laser beams 19A', 19B ', 19C' (in the direction of the fast axis here): this dimension corresponds at most to one fifth of the dimension of the optical mixing element (its entrance face) in this direction in order to provide a sufficient homogenization effect. In the case of a cylindrical lens, this homogenizing effect accordingly extends in the direction of curvature, for example over a fifth of the size of the optical light-mixing element 9.

the following Numerical Apertures (NA) can be assigned to the microlens arrangement 7 on the basis of the focal length f of the lenses 7A of the microlens arrangement 7 and on the basis of the offset/pitch p between adjacent lenses 7A (offset in the curvature direction in the case of cylindrical lenses):

NA _ microlens array is p/(2 f).

If the microlens arrangement 7 is arranged at a distance from the light-mixing elements 9 (for example at a distance of a few millimeters), the preferred dimensions of the lenses 7A in the direction of alignment of the laser beams 19A, 19B, 19C or in the direction of alignment of the laser beams 19A ', 19B ', 19C ' are such that the main pump laser beam 15A preferably radiates through at least five lenses. With such a positioning of the microlens arrangement 7, the microlens arrangement can be integrated, for example, into the diaphragm element 28 (see the microlens arrangement shown in fig. 1 in dashed lines in the diaphragm element 28).

In general, the offset of the adjacent lenses 7A of the microlens array 7 and the position of the microlens arrangement 7 in the beam path between the pump laser system 3 and the optical hybrid 9 are selected such that at least five lenses 7A of the microlens arrangement 7 are illuminated.

With regard to the angular distribution of the coupling-in light into the light-mixing element 9, there is again an angular distribution of the initially superimposed pump laser beam 15A on each facet (lens 7A) of the microlens arrangement 7. In the case of a non-telecentric configuration, the beam divergence is additionally steeper (aufsteilen) due to the numerical aperture of the microlens arrangement 7. For example, the beam divergence of the incidence in the direction of the fast axis is in the range of 140-220mrad, while the microlens arrangement 7 has a numerical aperture of, for example, 0.05. However, the angular distribution typically differs in the case of using a microlens device as follows: the new angular characteristic results from a plurality of positions on the beam cross-section, here from each irradiated facet, and not from just one position (corresponding pump module). In this way, a plurality of new sources arranged next to one another are generated directly in front of the light-mixing element 9, which sources enter the light-mixing element 9 at different points with a structured angular distribution, so that the homogenization can be significantly improved.

The light mixing element 9 homogenizes the input laser radiation by, for example, multiple reflections. That is to say, the optical light mixing element 9 is designed to mix the incoming laser beam by multiple reflections. As is schematically illustrated in fig. 1, the light-mixing element 9 is designed, for example, as a light mixer rod. In the light mixer rod, the light beam is guided by multiple reflections inside the light mixer rod from the entrance surface 29A of the light mixer rod to the exit surface 29B of the light mixer rod. The number of reflections of the light beams in the light mixer rod is generally dependent on the angle of incidence of the respective light beam, so that a homogenized (more homogenized) distribution of the emitted light beams is present at the exit surface 29B.

The cross section of the light mixer rod can be adapted to the respective application. Thus, in particular (substantially) rectangular and hexagonal or hexagonal type cross-sectional shapes can be used, which may be advantageous, for example, in combination with multiple passes through the laser medium. Fig. 1, for example, schematically shows a hexagonal intensity characteristic 30 of the homogenized pump laser beam 15B.

The material of the light mixer rod (for example optical quartz) is matched to the respective wavelength as the length of the light mixer rod used. An exemplary length of the light mixer bar is in the range of about 90mm to about 120mm, preferably in the range of about 100mm to about 110mm, for example 105 mm.

For example, in the case of a pump laser system configured to be equipped with a different number of pump modules, the length of the light-mixing element 9 and/or the number of lenses 7A radiated through are designed such that the intensity fluctuation of the homogenized pump laser beam 15B is less than 15%, for example less than 10% or less than 5%, in the case of a minimum number of pump modules provided in combination with the microlens arrangement 7.

In general, the microlens array 7 has a numerical aperture as follows: the numerical aperture does not significantly degrade the beam divergence, in particular in the fast axis direction, wherein the divergence in the slow axis direction is substantially unaffected in the case of a cylindrical lens array. In general, the numerical aperture of the microlens device in the fast axis direction is, for example, 0.2 to 0.7 times the numerical aperture of the light mixing element 9.

The homogenized pump laser beam 15B exiting from exit face 29B is collimated by one or more further optical devices 31 (e.g. one or more lenses) and focused onto the laser active medium 13 of the laser cavity.

Furthermore, the beam guidance of the homogenized pump laser beam 15B can be realized by means of the optics of the amplifier unit 11, for example by means of a focusing mirror 33 (for example a parabolic mirror) and a folding mirror 34.

In the amplifier unit 11, which is configured exemplarily as a disk laser cavity, the laser-active medium 13 is arranged on the cooling element 35. The focusing mirror 33 and the folding mirror 34 can pass the homogenized laser beam 15B through the laser active medium 13, for example, 8 times or more. Due to the multiple passage through the laser-active medium 13, a substantially rotationally symmetrical excitation profile (inversion) results in the laser-active medium 13, which is schematically illustrated, for example, by the intensity characteristic 37. Furthermore, an opening 39 is provided in the focusing mirror 33, through which the generated or amplified laser beam 41 is coupled out. Not shown in fig. 1 are beam guidance means for guiding seed laser pulses into the laser-active medium 13, for example. Other features of such a disk laser cavity are disclosed for example in EP 2686339B 1.

fig. 2A to 2C show the pump spots 51A of the homogenized pump laser beam 15B produced by a single pass in the case of (almost) complete assembly of the pump laser system (fig. 2A), and the pump spots 51B, 51C of the laser beam produced by a single pass (fig. 2B) and multiple passes (fig. 2C) in the case of partial assembly. In fig. 2A to 2C, a plurality of regions with the reference numbers I, II, III and IV are schematically provided for illustrating the structure in the pump spot, wherein the intensity/pump power present in the region increases from I to IV. Furthermore, a punctiform region can be identified in which no or only a small amount of intensity/pump power is present (for example in the edge region).

The pump spot 51A of fig. 2A enables a substantially constant pump power input, which can be achieved, for example, with more than five pump modules. In the cross-sectional intensity profile 53A, an almost constant intensity distribution can be seen by the pump spot 51A. For example, an approximate intensity distribution is also obtained with an arrangement of more than five pump modules and a variable intensity distribution of ± 10%.

fig. 2B likewise shows a relatively constant intensity distribution (pump spot 51B) as a function of the cross-sectional intensity characteristic 53B even for a partially equipped, for example, two pump modules, between which a beam-free region is also formed. In particular, no significant maxima are visible in the intensity distribution, which maxima may lead to specific structures in the intensity distribution after a corresponding pump laser beam has passed through the laser-active medium 13 several times.

Fig. 2C accordingly shows such a pump spot 51C that is formed on the laser disk after a plurality of passes. Due to the hexagonal configuration of the optical light mixing element and the stepwise rotation of the pump laser beam between the multiple passes, a substantially rotationally symmetrical intensity distribution is formed.

For comparison, fig. 3A to 3C show pump spots 55A, 55B, 55C in the case of direct coupling into the light-mixing element (i.e. without a microlens arrangement). The pump spot 55A in turn corresponds to a single pass in the case of an (almost) completely assembled pump laser system. A rhombus-shaped pattern can be seen in the intensity distribution, which results in a large fluctuation in the associated cross-sectional intensity characteristic 57A. This may lead to corresponding inhomogeneities in the excitation of the laser-active medium.

If the pump laser system is only partially assembled in the exemplary application and there is a beam-free region in the main pump laser beam, large fluctuations can be obtained. Thus, for example, in the case of only two pump modules, only two non-central maxima can be formed in the pump spot 55B, which maxima lie opposite one another. Likewise, the central superelevation is seen in the associated cross-sectional strength characteristic 57B. Both of which are features of incomplete homogenization. If one pump module is now replaced in such a case, the cross-sectional strength properties of another structure will be produced, resulting in new pump properties.

If such a pump laser beam of the now only partially assembled pump laser system passes through the laser-active medium 13 a plurality of times, a pump spot 55C, which is shown by way of example in fig. 3C, is formed. An intensity ring can be seen around the region of low intensity near the center. Furthermore, the strength ring is provided with an edge structure showing strength fluctuations.

If fig. 2A to 2C are compared with fig. 3A to 3C, it can be seen that the combination of the microlens arrangement and the light-mixing element enables a substantial homogenization of the pump radiation, in particular of the intensity distribution in the laser-active medium.

Furthermore, the optical beam shaping system 5 integrated into the pumping unit 2 disclosed herein may be used in high power amplifier systems (e.g. solid state laser systems). In addition to the disc laser system exemplarily depicted in fig. 1, the optical beam shaping system 5 can also be used in the laser geometry of laser active media in a plate-like or rod-like configuration, or for optical pumping of semiconductor lasers (typically in continuous and pulsed applications).

In an exemplary embodiment of the optical beam shaping system, a telecentric design of the lenticular array can be used as an example of a specific microlens arrangement that can minimize the effects of beam divergence and beam quality. In other words, in the case of a biconvex array of this telecentric design, two identical lenses are arranged at a pitch of 2f (front and rear) from one another, so that homogenization of the radiation is achieved without substantially steepening the numerical aperture.

It is expressly emphasized that for the purposes of original disclosure and also for the purposes of limitation of the claimed invention, independently of the combination of features in the embodiments and/or the claims, all features disclosed in the description and/or the claims are to be regarded as being separate and independent of one another. It is explicitly pointed out that for the purposes of the original disclosure and also for the purpose of limiting the invention to be protected, all region data or data of a group of cells disclose every possible intermediate value or subgroup of cells, in particular as a limitation of the region data.