DE102017108936A1 - Homogenization of pump laser radiation - Google Patents

Abstract

A pump unit (2) for generating a homogenized pump laser beam (15B) for optically pumping a laser-active medium (13) of a laser system (1) comprises a pump laser system (3) in which a plurality of laser beams (19A, 19B, 19C, 19A ', 19B ', 19C') to a primary pump laser beam (15A). Furthermore, the pump unit (2) comprises an optical beam-shaping system (5) for homogenizing the primary pump laser beam (15A), the optical beam-shaping system (5) comprising a microlens array (7) with a plurality of lenses (7A) and an optical light mixing element (9) Guiding the primary pump laser beam (15A) through multiple reflection and for delivering the homogenized pump laser beam (15B). The microlens array (7) is arranged such that the primary pump laser beam (15A) radiates through a plurality of lenses (7A) of the microlens array (7) prior to coupling into the optical light mixing element (9).

Description

The present invention relates to optical systems for the homogeneous superposition of laser radiation, in particular for the superimposition of pump laser radiation of a plurality of laser diode modules, as used in pump laser systems. Furthermore, the invention relates to laser systems, in particular laser systems pumped with diode lasers, for amplifying cw and pulsed laser radiation to high power and / or high pulse energy.

Laser systems, z. B. high-power solid-state lasers, require a correspondingly designed pump power, which is to be coupled into the gain of the underlying medium. In order to achieve high pumping powers, the laser radiation of several pump lasers can be superimposed to form a pump laser beam. Furthermore, the superimposed laser radiation from a plurality of laser diodes, a crystal, for. B. a disk-shaped gain medium of a disk laser amplifier, go through several times in a folded structure. Pump laser systems may be based on high power diode laser modules, each having a plurality of laser diode bars.

Combining laser radiation of several laser diodes can, for example, with a as in EP 2 342 596 B1 done concavity described. In this case, a pump module has diode bars arranged on top of each other 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 several pumping modules, the jet-free regions of a pumping module are filled up by the remaining pumping modules.

In compact diode bars reduce the beam-free areas, so that the output radiation of the pump modules to form a pump laser beam can be combined in a subsequent common beam path when the pump modules z. B. are arranged directly above one another.

Before the pump laser beam is coupled into the laser-active medium, the output radiation of the various pump modules, ie the different laser bars, can be mixed in a light mixer, whereby a more homogenous output beam profile of the homogenized pump laser beam can be generated after the light mixer. An exemplary laser pump arrangement with beam homogenization in an optical homogenizer for the mixing of partial pump radiation is shown in FIG WO 2010/052308 A1 disclosed.

To provide scalability of the pumping power of the pump laser system, the number of pumping modules used in an otherwise identical pump laser system can be varied depending on the application. With a reduced number of pumping modules, however, the angular range of the pumped laser beam coupled into the light mixer can be reduced so that the homogenization of the pumped laser beam can not be complete or insufficient for an application. This can lead to an increased sensitivity of a pumped laser system (eg laser amplification system) to the adjustment of the pump laser beam. For example, an increased sensitivity to changes in the beam path and / or in the intensity distribution occurs. The increased sensitivity may in particular be due to the fact that the power distribution in the pump beam changes when z. B. a pumping module is exchanged for another pumping module, wherein the new pumping module usually has a slightly different radiation behavior, in particular a slightly different Abstrahlwinkelverteilung has. If z. B. generally large angular ranges of the focused pumping light are not filled by laser beams may not be sufficient to make the homogenization in the light mixer. This can result in different pumping modules different power distributions, each of which is otherwise insufficient and so lead to instability or to a necessary readjustment of the system. For example, in the case of the abovementioned disk laser system, the power distribution in the amplification medium in a single pass is decisively responsible for the resonator stability and for the running-in behavior or the step response of the disk laser system.

One aspect of this disclosure is based on the object of proposing a pump unit for generating a homogenized pump laser beam, which is designed in particular for use with a different number of pump modules. The optical beam-shaping system for beam homogenization should in particular bring about an improvement in the homogenization with a small number of pump modules. In other words, even in the presence of jet-free areas of a pump laser beam to be homogenized, sufficient homogenization should take place. A further aspect of this disclosure is based on the object of increasing the stability of pump laser systems and correspondingly pumped laser systems, in particular laser amplification systems, and to simplify the replacement of pump modules.

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

In one aspect, a pump unit for generating a homogenized pump laser beam for optically pumping a laser active medium of a laser system comprises a pump laser system and an optical beam forming system. In the pump laser system, a plurality of laser beams are superimposed to a primary pump laser beam. The optical beam shaping system is for homogenizing the primary pump laser beam, the optical beam shaping system comprising a microlens array having a plurality of lenses and an optical light mixing element for guiding the primary pump laser beam through multiple reflection and for delivering the homogenized pump laser beam. The microlens array is arranged such that the primary pump laser beam irradiates a plurality of lenses of the microlens array prior to coupling into the optical light mixing element.

In a further aspect, a laser system, in particular a laser amplifier system, comprises such a pump unit and a laser cavity with the laser-active medium to be pumped, which radiates the homogenized pump laser beam generated by the pump unit at least once.

In exemplary embodiments, the pump laser system includes a plurality of pumping modules, each pumping module emitting a plurality of laser beams and generating the primary pumping laser beam by superposing the laser beams of the pumping modules.

In exemplary embodiments, a position of the microlens array in the beam path between the pump laser system and the optical light mixing element and a lateral offset of adjacent lenses of the microlens array are selected such that at least five lenses of the microlens array are illuminated. For example, the light mixing element has an entrance surface and an exit surface, and the microlens array is disposed directly on or near the entrance surface of the optical light mixing element. Furthermore, the microlens array can be arranged in the opening of a beam aperture element. In exemplary embodiments, lenses of the microlens array may be lined up in an alignment direction with an offset between two lenses, the offset corresponding to at most one fifth of the extent of an entrance surface of the optical light mixing element in the array direction.

In exemplary embodiments, the light mixing element is configured as a light mixer rod that guides light beams through total internal multiple reflections from an entrance surface of the light mixer rod to an exit surface of the light mixer rod through the light mixer rod, and a number of reflections of a light beam in the light mixer rod depend on the incident angle of the respective light beam on the entrance surface. so that there is a homogenized distribution of the emerging light rays at the exit surface.

In exemplary embodiments, the pump laser system is configured to be populated with a different number of pumping modules, and a length of the light mixing element and the number of irradiated lenses are such that when using a minimum number of pumping modules in combination with the microlens array, an intensity variation in the homogenized pump laser beam of less than 15%.

In general, a numerical aperture of the microlens array can be adapted to the divergence of the primary pump beam.

In some example embodiments, the pumping unit may further include focusing optics for generating a convergent beam path for coupling the primary pump laser beam into the light mixing element, the microlens array being disposed in the convergent beam path between the focusing optics and the light mixing element in a region of the at least substantially superimposed laser beams of the pump laser system ,

In some example embodiments, the pump laser system may include a plurality of laser diode based pumping modules. A laser beam region can then be assigned in each case to a pump module of the plurality of pump modules, wherein adjacent (in particular flatly closed) laser beam regions in the primary pump laser beam are arranged next to one another in the direction of the fast axis prior to the superposition. The laser diode-based pumping modules can be arranged side by side in the direction of the fast axis, so that the laser radiation from adjacent pumping modules forms adjacent regions of the primary pumping laser beam prior to the superposition. Alternatively, the laser radiation can be guided by pump modules in such a way that adjacent laser beam areas of the primary pump laser beam are generated by respectively assigned pump modules and aligned next to one another by means of optics.

In some example embodiments, the pump laser system may include a plurality of laser diode-based pumping modules each having a plurality of diode bars for emission Laser beams include, wherein in the primary pump laser beam, the laser beams of a diode bar of a pump module in a direction of the fast axis of the diode bar spaced from each other and are mutually intermeshed with respect to the plurality of pumping modules. Thus, the pump unit may further comprise an optical arrangement for combing the laser radiation of different pump modules, so that the laser radiation of diode bars of different pump modules form superimposed adjacent contributions of the primary pump laser beam.

In exemplary embodiments, the microlens array is formed as an array of cylindrical lenses and the cylindrical lenses are aligned for focusing in the direction of the fast axis.

The embodiments disclosed herein may include: a. improve the running-in behavior of a disk laser system and thus enable a more stable and efficient operation of the disk laser system. Furthermore, the microlens array (microlens array) in front of the light mixing element can bring about a more independent and improved homogenization from the angle space.

• 1 eine schematische Darstellung eines beispielhaften Laserverstärkersystems mit einem optischen Strahlformungssystem zur Strahlhomogenisierung,
• 2A bis 2C schematische Darstellungen von Strahlprofilen (Pumpflecken) zur Verbesserung der Homogenisierung mithilfe einer Mikrolinsenanordnung und
• 3A bis 3C schematische Darstellungen von Strahlprofilen (Pumpflecken) mit Homogenisierung ohne Verwendung einer Mikrolinsenanordnung.

Herein, concepts are disclosed that allow to at least partially improve aspects of the prior art. In particular, further features and their expediencies emerge from the following description of embodiments with reference to the figures. From the figures show:

• 1 a schematic representation of an exemplary laser amplifier system with an optical beam shaping system for beam homogenization,
• 2A to 2C schematic representations of beam profiles (Pumpflecken) to improve the homogenization using a microlens array and
• 3A to 3C schematic representations of beam profiles (Pumpflecken) with homogenization without the use of a microlens array.

Aspects described herein are based, in part, on the finding that a microlens array (also referred to as a microlens array) can make the pump laser beam introduced into a light mixing element in angular distribution independent of the number of pumping modules used for angular distribution, which is better Homogenization causes. The microlens array makes the homogenization generally more independent of the primary pump laser beam. In particular, the inventors have recognized that an optical beam shaping system for homogenizing a pump laser beam is to be designed in such a way that sufficient homogenization is to take place independently of the number of laser radiation contributions used. In particular, with an array of output jets of pumping modules positioned side-by-side or one above the other, larger areas in the jet pattern of the primary pumping laser beam near the pumping modules may remain jet-free in particular if fewer pumping modules than necessary for complete illumination of the steel profile are used , It has been recognized that a combination of a microlens array, such as an array of cylindrical lenses, with a light mixing element can achieve sufficient beam homogenization despite lack of coverage of the cross section of the primary pump laser beam prior to being superimposed with laser beam contributions from pumping modules.

The optical beam shaping system of a pump unit proposed herein can be advantageously used in particular for a vertical stacking of laser radiation contributions, which is not based on combing the laser radiation of the respective laser bars, but an optical or structural stacking of the laser radiation contributions of several laser bars of a pumping module or the output beams of several pumping modules. As a result, in both cases stacking of laser contributions ("stack" of laser contributions) usually results in the direction of the fast axis.

Such a compact arrangement of laser bars enables a simple coupling-in optics of the radiation emanating from these vertical stacks in a (for example, almost rotationally symmetrical) light mixing element with approximately maintaining the brilliance of the pump radiation. Further, by virtue of the combination with a microlens array proposed herein, the beamforming system is also applicable where the vertical stacking of pumping modules does not provide laser beam contributions over the entire beam cross section before interference of the primary pumping laser beam, since the microlens array provides sufficient distribution of the angular contributions of laser beams preceding the input beam Form light mixing element produced.

The following will be in connection with the 1 and 2 the pump beam shaping and the amplification process as well as the associated components of an exemplary laser system 1 with the concept disclosed herein for an optical beam forming system. 3 shows for comparison the beam development in a corresponding structure without microlens array.

The laser system 1 includes a pump unit 2 that is a pump laser system 3 with a plurality of pumping modules 3A . 3B . 3C and an optical beam-forming system 5 having. The optical beam-forming system 5 includes, among other things, a microlens array 7 and a light mixing element 9 on. The laser system 1 further comprises an amplifier unit 11 (generally laser cavity) with a laser-active medium 13 , Generally, the pump laser system generates 3 a primary pump laser beam 15A that with the optical beam shaping system 5 to the respective desired pumping of the laser-active medium 13 is adjusted. Further features of the respective units are explained in more detail below in connection.

The pump modules 3A . 3B . 3C For example, they may be formed as laser diode modules. Generally, diode laser radiation allows efficient pumping of the laser active medium 13 , wherein the primary pump laser beam 15A is formed by superposition of diode laser radiation of a plurality of laser diode modules, generally the laser radiation of a plurality of pump modules. In 1 are exemplary of the three pumping modules 3A . 3B . 3C shown schematically arranged side by side.

A pump module designed as a laser diode module comprises a plurality of laser bars, each laser bar having a plurality of emitter zones. The laser bars of a pumping module may, for example, form a structural stack in which the emitter zones of the laser bars are arranged in the direction of the fast axis substantially without offset in the slow axis, so that the output radiation of the laser bars of a pumping module are stacked in the direction of the fast axis. Alternatively, the emitter zones of the laser bars may be placed in a pumping module with an offset in the slow axis, then by optical stacking with z. B. deflecting mirrors and / or prisms can also be achieved that the output radiation of the laser bars of a pumping module are stacked in the direction of the fast axis (optical stack).

In older Pumpmodularchitekturen the laser bars are so far apart that z. B. the aforementioned combing laser radiation of several pump modules is used to produce the primary pump laser beam. Recent pump modular architectures, in which the size of a single laser bar has been reduced so that the size of a single pumping module can be reduced to a few millimeters in the direction of the fast axis, now allow multiple pumping modules to be placed close to one another, e.g. B. in the direction of the fast axis directly next to each other, can be arranged. So can be dispensed with in the generation of the primary pump laser beam on the combing, while still due to the spatial proximity of the laser bar and pumping modules, a primary pump laser beam with a z. B. can be generated substantially rectangular cross-section.

Typically, the diode laser radiation of multiple laser diode modules is assembled to provide a primary pump laser beam having a rectangular cross-section. This can be formed, for example, to a uniform round Pumpfleck or generally to a uniform round excitation of the laser-active medium 13 , Such a beam transformation takes place, inter alia, with the light mixing element 9 , Thus, for example, pump modules which are designed as the previously mentioned optical and / or structural stacks can be arranged lined up in the direction of the fast axis, so that the desired beam cross section of the primary pump laser beam results. Alternatively, such pump modules can be arranged as desired and the associated diode radiations of the different pump modules can be brought together optically next to one another to form the primary pump laser beam.

1 schematically shows exemplary beam cross-sections of the primary pump laser beam 15A for different embodiments of the pump laser system 3 ,

So refer to beam cross-sections 17A . 17B to the example of the above-mentioned entanglement of laser radiation of several pump modules, when fully equipped with three pump modules (beam cross section 17A ), as well as when partially equipped with two pump modules (beam cross section 17B ).

In the beam cross section 17A of the primary pump laser beam 15A By way of example, one recognizes three groups of laser beams 19A . 19B . 19C , each one of the three pumping modules 3A . 3B . 3C assigned. Each of the laser beams 19A . 19B . 19C originates from a laser bar, due to the pump module structure, the laser beams of a group are emitted from each other with a distance. The elliptical shape of the beam profiles of the laser beams 19A . 19B . 19C results from the different optical properties of fast axis and slow axis of diode laser beam generation. Thus, the laser light of an individual emission zone of the laser bar diverges more in the direction of the fast axis than in the direction of the slow axis, which is known to be due to the geometry of the emission zone and the laser process.

With a mirror arrangement, as shown for example in the above-mentioned EP 2 342 596 B1 can be described, the laser beams 19A . 19B . 19C be interleaved in such a way that, in spite of the elliptical beam profile of each laser bar a substantially rectangular in cross-section, in particular substantially square intensity distribution is generated. This is illustrated, for example, in the beam cross section 17A, which corresponds to a complete assembly.

Beam superposition by means of combing is customary in particular when the distances of the laser bars of a pumping module are in the range of a few millimeters.

Pumping the laser-active medium 9 with a primary pump laser beam thus produced by combing 15A represents a special challenge for the homogenization of an incomplete assembly with pump modules. In the case of incomplete assembly with pump modules, for example, the laser beams are omitted 19C , so that in the square beam cross-section 17B non-blasting areas 21 form. These non-blasting areas 21 could without the use of a microlens array, the light mixing element 9 reduce coupled angular distribution such that the homogenization in the light mixer in the case of incomplete placement to an inhomogeneous pump beam profile, especially in the laser-active medium 13 , could lead.

In the case of compact pump modular architectures shows 1 exemplary beam cross sections 23A . 23B , In an arrangement of, for example, designed as a structural or optical stacks pumping modules each pumping module, a laser beam range 25A . 25B . 25C in the primary pump laser beam 15A be assigned. Each laser beam area 25A . 25B . 25C includes a variety of laser beams 19A ' . 19B ' . 19C ' with elliptical beam profiles generated by the respective diode bars of the pumping module. Beam cross section 23A corresponds to a complete assembly, ie, a fully illuminated before superimposing cross section of the primary pump laser beam 15A ,

Even with such a pump module architecture, one or more beam-free areas can be used for incomplete assembly 21 present, as in the beam cross section 23B is indicated. Accordingly, even in such embodiments of a pump laser system 3 without using a microlens array reduced angular distributions in the light mixing element 9 be coupled.

The combed laser beams 19A . 19B . 19C or the laser beams 19A ' . 19B ' . 19C ' the laser beam areas 25A . 25B . 25C For example, with (deflecting) mirrors and a telescope arrangement for coupling into the light mixing element 9 superimposed.

The effects of the microlens array 7 on the homogenization are described below in connection with the 2 and 3 described. Previously, other components of the optical beam forming system 5 and the amplifier unit 11 described.

In 1 is representative of a usually multiple optical elements comprehensive focusing optics a lens 27 shown the primary pump laser beam 15A in the light mixing element 9 focused. In the illustrated embodiment, this causes before the light mixing element 9 arranged microlens array 7 (with schematically illustrated lenses 7A ) exemplifies a slight beam expansion of the primary pump laser beam 15A in the direction of the fast axis (here, for example, in the plane of the drawing). However, in general, other types of lenses may also be used 7A in the microlens array 7 For example, in focusing or expanding cylindrical lens arrays, lead to effects that improve the homogenization.

When the microlens array 7 directly on or near the entrance surface of the optical light mixing element 9 is arranged (see in 1 Dashed line indicated microlens element 7 ' on light mixing element 9 ), the respective lenses have z. B. in the direction of the alignment of the laser beams 19A . 19B . 19C or the laser beams 19A ', 19B', 19C '(here in the direction of the fast axis) have an extent equal to or less than one fifth of the extent of the optical light mixing element (its entrance surface) in this direction to provide a sufficient homogenizing effect. In the case of cylindrical lenses, for example, they extend in the direction of the curvature, for example over one fifth of the extent of the optical light mixing element 9 ,

The microlens array 7 may be a numerical aperture based on the focal length f of the lenses 7A the microlens array 7 and the offset / pitch p between adjacent lenses 7A (Offset in cylindrical lenses in the direction of curvature) are assigned: NA_Mikrolinsenarray = p / (2f).

Will the microlens array 7 with a distance to the light mixing element 9 arranged (for example, at a distance of a few millimeters) is a preferred extent of a lens 7A in the direction of the alignment of the laser beams 19A . 19B . 19C or the laser beams 19A ' . 19B ' . 19C ' such that preferably at least five lenses from the primary pump laser beam 15A be irradiated. In such a positioning of the microlens array 7 This can for example be in an aperture element 28 be integrated (see in 1 Dashed line indicated microlens element in aperture element 28 ).

Generally, there is an offset of adjacent lenses 7A the microlens array 7 and a position of the microlens array 7 in the beam path between the pump laser system 3 and the optical light mixing element 9 chosen such that at least five lenses 7A the microlens array 7 be lit up.

With regard to the angular distribution in the light mixing element 9 is coupled, lies on each facet (lens 7A ) of the microlens array 7 again the angular distribution of the original superimposed pump laser beam 15A at. In a non-telecentric setup, the beam divergence is additionally enhanced by the numerical aperture of the microlens array 7 steepened. For example, the incident beam divergence in the direction of the fast axis is in the range of 140-220 mrad and the microlens array 7 has a NA of z. B. 0.05. However, generally when using a microlens array, the angular distribution is now with the difference that new angle profiles come from multiple locations across the beam cross-section, here each illuminated facet, and not just one location (the respective pumping modules). This results directly in front of the light mixing element 9 several juxtaposed new sources, with the trained angular distribution at different locations in the light mixing element 9 occur, so that the homogenization can significantly improve.

The light mixing element 9 causes a homogenization of the coupled laser radiation z. B. by multiple reflection. That is, the optical light mixing element 9 is designed for mixing of incoming laser beams by multiple reflection. For example, the light mixing element 9 , as in 1 indicated schematically, designed as a light mixer rod. In the light mixing rod, light rays become total internal multiple reflection from an entrance surface 29A of the light mixer rod to an exit surface 29B led the light mixer rod. In general, the number of reflections of a light beam in the light mixer rod depends on the angle of incidence of the respective light beam, so that at the exit surface 29B a homogenized (re) distribution of the exiting light rays is present.

The cross section of the light mixer rod can be adapted to the respective application. Thus, in particular (essentially) rectangular and hexagonal or hexagonal-like cross-sectional shapes, which z. B. in connection with multiple passes through a laser media may be advantageous used. In 1 is an example of a hexagonal intensity profile 30 of the homogenized pump laser beam 15B shown schematically.

The material of a light mixer rod (eg, optical quartz) is matched to the appropriate wavelengths, as well as the lengths of the light mixer rod used. Exemplary lengths of a light mixer rod are in the range of about 90 mm to about 120 mm, preferably in the range of about 100 mm to about 110, such as at 105 mm.

For example, in a pump laser system configured to be populated with a different number of pumping modules, a length of the light mixing element is 9 and / or the number of irradiated lenses 7A designed so that when using a minimum number of pumping modules in combination with the microlens array 7 an intensity fluctuation in the homogenized pump laser beam 15B of less than 15%, such as B. is less than 10% or less than 5%.

Generally, the microlens array 7 a numerical aperture that does not significantly degrade the beam divergence, particularly in the direction of the fast axis, and in a cylindrical lens array, the divergence in the direction of the slow axis is substantially unaffected. Usually, the numerical aperture of the microlens array in the direction of the fast axis z. B. a factor in the range of about 0.2 to 0.7 of the numerical aperture of the light mixing element 9 on.

The out of the exit surface 29B exiting homogenized pump laser beam 15B is through one or more other optics 31 , For example, one or more lenses collimated, and on the laser-active medium 13 the laser cavity focused.

The beam guidance of the homogenized pump laser beam 15B can also with optics of the amplifier unit 11 done, such as with a focusing mirror 33 (eg a parabolic mirror) and folding mirrors 34 ,

In the exemplified as Scheibenlaserkavität amplifier unit 11 is the laser-active medium 13 on a cooling element 35 arranged. The focusing mirror 33 and the folding mirrors 34 For example, 8 or more passes of the homogenized laser beam 15B through the laser-active medium 13 enable. Due to multiple passes through the laser-active medium 13 results in a substantially rotationally symmetric excitation distribution (inversion) in the laser-active medium 13 as exemplified by an intensity profile 37 is illustrated schematically. Furthermore, in the focusing mirror 33 an opening 39 provided by the one generated or amplified laser beam 41 is decoupled. A beam guide for a z. B. Seed laser pulse in the laser-active medium 13 is in 1 not shown. Other features of such a Scheibenlaserkavität are for example in the EP 2 686 339 B 1 discloses.

The 2A to 2C show a pump leak 51A a homogenized pump laser beam generated by a single pass 15B in the case of (almost) complete placement of a pump laser system ( 2A ) as well as pump licks 51B . 51C with partial assembly for a single pass ( 2 B ) and a multitude of passes ( 2C ). In the 2A to 2C are schematically several zones with the reference numerals I, II, III and IV provided to illustrate a structure in the pump lumps, wherein the present in the zones intensity / pump power increases from I to IV. Furthermore, dotted areas can be recognized in which there is no or only a low intensity / pump power (for example, in the edge area).

The pump leak 51A of the 2A causes a substantially constant pump power input, as can be achieved, for example, when using more than five pumping modules. In a cross-sectional intensity profile 53A through the pump leak 51A one recognizes a nearly constant intensity distribution. A similar intensity distribution results z. B. even with an arrangement of more than five pumping modules and a variable intensity distribution of ± 10%.

Also, in the case of a partial assembly with, for example, two pumping modules, between which has formed a non-beam area shows 2 B a likewise relatively constant intensity distribution (Pumpfleck 51B ), as the cross-sectional intensity profile 53B underlying. In particular, no pronounced maxima in the intensity distribution can be seen which lead to specific structures in the intensity distribution after a multiplicity of passes of a corresponding pump laser beam through the laser-active medium 13 could lead.

According to shows 2C the pump leak 51C how it forms on the laser disk after a multitude of passes. Due to the hexagonal design of the optical light mixing element and a stepwise rotation of the pump laser beam between passages, a substantially rotationally symmetrical intensity distribution is formed.

For comparison show 3A to 3C pump spots 55A . 55B . 55C with a direct coupling into the light mixing element, ie, without a microlens arrangement. pump spot 55A again corresponds to a single pass with (almost) complete placement of the pump laser system. One recognizes a karoartiges pattern in the intensity distribution, which in the associated cross-sectional intensity profile 57A leads to larger fluctuations. These can lead to a corresponding inhomogeneity in the excitation of the laser-active medium.

If the pump laser system is only partially populated in an exemplary application and there are non-beam areas in the primary pump laser beam, larger variations may result. For example, when using only two pump modules, two decentralized, opposite maxima in the pump leak can occur 55B form. Likewise one recognizes in the assigned cross section intensity profile 57B a central elevation. Both are signs of incomplete homogenization. If a pump module is exchanged in such a case, a different structured cross-sectional intensity profile may result, which leads to a new pumping behavior.

Now passes through such a pump laser beam of a partially populated Pumplasersystems the laser-active medium 13 several times, a pump leak forms 55C from that exemplifies in 3C is shown. One recognizes an intensity ring which surrounds a region of lower intensity near the center. Furthermore, the intensity ring is provided with intensity fluctuations indicating edge structures.

Comparing the 2A to 2C with the 3A to 3C , it can be seen that the combination microlens array and light mixing element can substantially homogenize the pump radiation and in particular the intensity distribution in the laser-active medium.

The optical beam-forming system disclosed herein 5 , integrated in the pump unit 2 , can be used inter alia in a high power amplifier system, for example in a solid state laser system. In addition to the example in 1 sketched disk laser system, the optical beam shaping system 5 in laser geometries with laser-active media in slab or rod configuration or for the optical pumping of semiconductor lasers (generally in cw and pulsed applications).

In an exemplary embodiment of an optical beamforming system, a telecentric biconvex array may be used as an example of a specific microlens array that minimizes the effect on beam divergence and beam quality. In other words, in such a telecentrically designed biconvex array, two identical lenses (front and behind) in the distance 2f arranged to each other, so that a homogenization of the radiation is effected substantially without division of the numerical aperture.

It is explicitly pointed out that all features disclosed in the description and / or the claims are considered separate and independent of each other for the purpose of original disclosure as well as for the purpose of limiting the claimed invention independently of the feature combinations in the embodiments and / or the claims should. It is explicitly stated that all range indications or indications of groups of units disclose every possible intermediate value or subgroup of units for the purpose of the original disclosure as well as for the purpose of restricting the claimed invention, in particular also as the limit of a range indication.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2342596 B1 [0003, 0034]
• WO 2010/052308 A1 [0005]
• EP 2686339 [0054]

Claims (19)

Pump unit (2) for generating a homogenized pump laser beam (15B) for optically pumping a laser-active medium (13) of a laser system (1) with: a pump laser system (3) in which a plurality of laser beams (19A, 19B, 19C, 19A ', 19B', 19C ') are superimposed to a primary pump laser beam (15A), and an optical beam shaping system (5) for homogenizing the primary pump laser beam (15A), the optical beam shaping system (5) comprising a microlens array (7) having a plurality of lenses (7A) and an optical light mixing element (9) for guiding the primary pump laser beam (15A) by multiple reflection and to deliver the homogenized pump laser beam (15B), and wherein the microlens array (7) is arranged such that the primary pump laser beam (15A) irradiates a plurality of lenses (7A) of the microlens array (7) prior to being coupled into the optical light mixing element (9). Pump unit (2) after Claim 1 wherein the pump laser system (3) comprises a plurality of pumping modules (3A, 3B, 3C), each pump module (3A, 3B, 3C) emits a plurality of laser beams (19A, 19B, 19C, 19A ', 19B', 19C ') and primary pump laser beam (15A) is generated by superposition of the laser beams (19A, 19B, 19C, 19A ', 19B', 19C ') of the pumping modules (3A, 3B, 3C). Pump unit (2) according to one of the preceding claims, wherein a position of the microlens array (7) in the beam path between the pump laser system (3) and the optical light mixing element (9) and a lateral offset of adjacent lenses (7A) of the microlens array (7) are selected in that at least five lenses (7A) of the microlens array (7) are illuminated. Pump unit (2) according to one of the preceding claims, wherein the light mixing element (9) has an entrance surface (29A) and an exit surface (29B), and the microlens array (7) is located directly on or near the entrance surface of the optical light mixing element (9). Pump unit (2) after Claim 4 in that the lens (7A) of the microlens array (7) is aligned in a line-up direction with an offset between two lenses (7A) which is at most one fifth of the extent of the entrance surface (29A) in the array direction. Pumping unit (2) according to one of the preceding claims, wherein the microlens arrangement (7) is an array of cylindrical lenses. Pumping unit (2) according to one of the preceding claims, wherein the microlens arrangement (7) is arranged in the opening of a jet diaphragm element (28). Pump unit (2) according to one of the preceding claims, wherein the microlens array (7) is a telecentrically designed biconvex microlens array. Pumping unit (2) according to one of the preceding claims, wherein the light mixing element (9) is designed as a light mixer rod, the light rays by total internal multiple reflections from an entrance surface (29A) of the light mixer rod to an exit surface (29B) of the light mixer rod through the light mixer rod leads, and a Number of reflections of a light beam in the light mixer rod from the angle of incidence of the respective light beam on the entrance surface (29A) depends, so that at the exit surface (29B) is a homogenized distribution of the exiting light beams. Pump unit (2) according to one of the preceding claims, wherein the pump laser system (3) is designed to be equipped with a different number of pump modules (3A, 3B, 3C) and a length of the light mixing element (9) and the number of lenses (7A) irradiated. are designed so that when using a minimally provided number of pump modules (3A, 3B, 3C) in combination with the microlens array (7) an intensity variation in the homogenized pump laser beam (15B) of less than 15% is present. Pumping unit (2) according to one of the preceding claims, wherein a numerical aperture of the microlens array (7) is adapted to the divergence of the primary pumping beam (15A). Pumping unit (2) according to one of the preceding claims, further comprising a focusing optics (27) for generating a convergent beam path for coupling the primary pump laser beam (15A) into the light mixing element (9), wherein the microlens array (7) in the convergent beam path between the focusing optics (27) and the light mixing element (9) in a region of at least substantially superposed laser beams (19A, 19B, 19C, 19A ', 19B', 19C ') of the pump laser system (3 ) is arranged. Pumping unit (2) according to one of the preceding claims, wherein the pump laser system (3) comprises a plurality of laser diode-based pumping modules (3A, 3B, 3C) and a laser beam area (25A, 25B, 25C) respectively a pumping module of the plurality of pumping modules (3A , 3B, 3C), wherein adjacent laser beam areas (25A, 25B, 25C) are juxtaposed in the primary pump laser beam (15A) before being superimposed in the direction of the fast axis. Pump unit (2) after Claim 13 wherein the laser diode-based pumping modules (3A, 3B, 3C) are juxtaposed in the fast axis direction such that the laser radiations from adjacent pumping modules (3A, 3B, 3C) form adjacent areas of the primary pumping laser beam (15A) prior to interference, or wherein the laser radiation from pump modules (3A, 3B, 3C) is guided in such a way that adjacent laser beam areas (25A, 25B, 25C) of the primary pump laser beam (15A) are generated by associated pump modules (3A, 3B, 3C) and aligned next to one another by means of optics become. Pump unit (2) according to one of Claims 1 to 12 wherein the pump laser system (3) comprises a plurality of laser diode based pumping modules (3A, 3B, 3C) each having a plurality of diode bars for emitting the laser beams (19A, 19B, 19C, 19A ', 19B', 19C ') in the primary pump laser beam (15A), the laser beams (19A, 19B, 19C, 19A ', 19B', 19C ') of a diode bar of a pump module (3A, 3B, 3C) are spaced apart from each other in a direction of the fast axis of the diode bars and in plural of pumping modules (3A, 3B, 3C) are intermeshed with each other. Pump unit (2) after Claim 15 and further comprising an optical arrangement for combing the laser radiation of different pumping modules (3A, 3B, 3C) such that the laser beams of diode bars of different pumping modules (3A, 3B, 3C) form juxtaposed contributions of the primary pumping laser beam (15A) before being superimposed. Pump unit (2) according to one of Claims 13 to 16 wherein the microlens array (7) is formed as an array of cylindrical lenses and the cylindrical lenses are aligned for focusing in the direction of the fast axis. Laser system (1), in particular laser amplifier system, with a pump unit (2) according to one of Claims 1 to 17 , and a laser cavity (11) with the laser-active medium (13) to be pumped, which radiates the homogenized pump laser beam (15B) generated by the pump unit (2) at least once. Laser system (1) after Claim 18 wherein the homogenized pump laser beam (15B) is rotated between successive passes through the laser active medium (13).

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