WO2007056999A2

WO2007056999A2 - Solid laser system and method for the operation thereof

Info

Publication number: WO2007056999A2
Application number: PCT/DE2006/002027
Authority: WO
Inventors: Stephan Strohmaier; Hans Joachim Eichler; Klaus Petermann; Günter Huber
Original assignee: Technische Universität Berlin
Priority date: 2005-11-17
Filing date: 2006-11-17
Publication date: 2007-05-24
Also published as: WO2007056999A3

Abstract

The invention relates to a solid laser system with a longitudinal excitation configuration, as well as to a method for operating it. The solid laser has the following features: a laser medium (1), which is arrangement inside a laser resonator (5) and formed from a laser-active solid material, and excitation source (2) with a laser diode arrangement that is configured for generating pulsed excitation beams, and; a fiber launching device, which is configured for launching pulsed excitation beams from the excitation source (2) along the optical axis of the laser resonator (5) into the laser medium (1). The laser diode arrangement is configured in such a manner that the pulsed excitation beams are supplied with a pulse peak power of at least 400 W.

Description

Solid state laser system and method of operation

The invention relates to a solid-state laser system and a method for operating the solid state lasersy stems.

Background of the invention

Solid state laser systems can be divided into systems having a transverse or a longitudinal pumping configuration. In order to excite a laser-active material, energy in the form of light is coupled into the laser-active material. This is usually done by means of continuous discharge lamps and flashlamps or by means of continuous (cw) laser diodes. Commercially available lamp-pumped laser systems deliver average output powers up to the kW range and pulse energies of over 100 mJ with total efficiencies of 2 to 5%.

With the help of the use of laser diodes as pumping or excitation source, with a good match of the wavelength of the pumping light to the absorption of the laser-active ion, a high efficiency of more than 30% can be achieved, i. the power or energy of the pump / excitation laser radiation is converted to more than 30% in solid state laser radiation. However, the achievable pulse energies are usually only in the range of .mu.J to a few mJ, since the pump sources in the range of the life of the upper laser level of the laser-active material can provide little pumping energy.

High pulse energies can be achieved by transversal pumping with pulsed laser diodes. However, the efficiencies are very small here.

Transversely pumped bar lasers are known. This concept was adopted by older lamp-pumped laser systems. In the transverse construction, the pump energy is coupled from the side into a rod made of the laser-active material. This allows the coupling of high average power, but leads to relatively low efficiencies. The diode pump light is converted to about 20% in laser radiation. The efficiency is even lower in the known bar lasers, if by means of mode apertures a good beam quality is enforced. Compared to the lamp-pumped systems, there is the advantage that the tuning between the wavelength of the pump source and the absorption of the laser-active material can be improved with the laser diode as the pump source. It must therefore be dissipated less heat, whereby thermal problems are reduced. In addition, a significantly better beam quality is achieved. Furthermore, there is the advantage that a simple construction is made possible in comparison to lamp-pumped laser systems. In transversally diode-pumped laser systems with pulsed excitation beams, pulse energies of more than a hundred mJ are achieved. However, this happens with little efficiency. In addition, the beam quality of the generated laser radiation is poor.

Solid state laser systems are also known in which a longitudinal pump configuration is formed so that the excitation beams are coupled along the optical axis of the laser beams. In this case, the pump excitation beam volume can be adapted to the mode volume of the laser beam, whereby, for example, in a Nd: YAG laser system, a high efficiency of up to about 50% with good beam quality can be achieved. In the known solid-state laser systems, a continuous excitation radiation (cw radiation) of the laser diodes is used. A pulse operation is achieved by means of additional Q-switching. The pulse output energies thus achieved are at most about 1 mJ.

In addition, it is known to pulse pulsed laser diodes with up to about 50 W average power, so that peak pulse powers of about 100 W are achieved. With this, a pulsed Nd: YAG solid-state laser system can achieve a maximum output energy of approximately 10 mJ and pulse durations of less than 200 μs.

As a diode-pumped laser system, the so-called slab laser is still known. In this concept, the laser-active material is provided in the form of a slab, for example, having the dimensions 16 mm × 8 mm × 3 mm A particular advantage of the slab laser is that good power scalability is maintained at a high level In addition, heat can be dissipated well and the adaptability to pump sources is advantageous, for example to a laser diode array For example, with a continuously diode-pumped slab laser system with Q-switching a maximum output energy of 1.8 mJ was achieved (cf. KJ Snell et al: Highly Efficient, Transversely-Pumped, 25W, TEM00 Nd: YLF Slab Laser, in: Conference on Lasers and Electro-Optics, OSA Technical Digest (Optical Society of America, Washington, DC, 2000), pp. 200-201).

As diode-pumped solid-state lasers, disk lasers are furthermore known. In these laser systems, a thin disc, for example, having a diameter of 10 mm and a thickness of 0.1 mm, applied directly to a heat sink. As a result, heat can be removed very quickly, and thermal lens effects that cause deterioration of the beam quality of the generated laser radiation can be almost avoided. By means of mirroring the crystal of the laser-active material, the pumping light can pass through the crystal several times. Despite the small thickness of the disc, a high efficiency is achieved. Disk lasers with a power output of 4 kW in a multimode beam are commercially available. In mode-locked laser systems, an average output power of 80 W was achieved (see Brunner et al., Opt. Lett., 29 (16), 1921 (2004)).

Fiber-lasers are furthermore known as diode-pumped solid-state laser systems. Laser glasses can be pulled out to thin glass fibers. The end faces of the glass fiber are mirrored on one side highly reflective for light of the emission wavelength of the laser active material and highly transmissive for light of the wavelength of the excitation beams. On the other side of the glass fiber, a multilayer system with the desired degree of decoupling is applied. Due to their large length, for example 10 m, the glass fibers have a large surface area, which allows very good heat dissipation. When using single-mode fibers, diffraction-limited fundamental mode radiation can be achieved. In continuous operation, output powers in the kilowatt range are achieved with high beam quality. The diameter and thus the surface of the fiber core is limited to about 50 microns. Compared to bar fibers, the surface is therefore smaller by two to three orders of magnitude. The energy density is therefore already at an impulse energy of 1 mJ at 80 J / cm ² , which already reaches the range of the destruction threshold of the active laser material. Even with fiber end caps, only pulse energies of a few mJ can be achieved.

In summary, in longitudinally pumped solid-state laser systems in the form of a bar laser, a slab laser, a disk laser or a fiber laser, pulse energies of less than 20 mJ are achieved. In contrast, transversely pumped bar lasers achieve pulse energies of about 100 mJ, however, have a poor efficiency. In addition, the achievement of good beam quality is difficult in the known lasers. In addition, measures to improve the beam quality further reduce the efficiency.

The document DE 102 35 713 A1 discloses a device for pump excitation of a laser medium via laser diode stacks. A plurality of laser diode stacks, which individually comprise a plurality of laser diode bars, are arranged around the optical axis at a distance from the optical axis of a resonator with the laser medium to be pumped. The pump light emitted by the laser diode stacks is coupled into the laser medium via mirror arrangements at a small angle to the optical axis.

Document US 2003/0138005 A1 describes a solid-state laser system which is excited on an ion-longitudinal basis by means of a pulsed laser diode source. A longitudinal pump excitation by means of laser diode arrangements is also known from document US 2004/0052284 A1.

Summary of the invention

The object of the invention is therefore to provide a solid-state laser system and a method for operating the solid-state laser system, with which high pulse energies can be generated and at the same time a high efficiency and good beam quality of the laser radiation generated can be achieved.

This object is achieved by a solid-state laser system according to independent claim 1 and a method for operating a solid-state laser system according to independent claim 16.

According to one aspect of the invention, there is provided a solid state laser system having a longitudinal excitation configuration having the following features:

a laser medium which is arranged in a laser resonator and formed from a laser-active solid-state material, an excitation source having a laser diode array configured to generate pulsed excitation beams, and

a fiber launch means configured to couple the pulsed excitation beams from the excitation source along the optical axis of the laser cavity into the laser medium, the laser diode array being arranged to emit the pulsed excitation beams with a peak pulse power of at least 400W.

According to another aspect of the invention, there is provided a method of operating a solid state laser system having a longitudinal excitation configuration comprising a lasing medium disposed in a laser resonator and formed of a solid state laser active material, the method comprising:

pulsed excitation beams are generated by an excitation source with a laser diode array, and the pulsed excitation beams from the excitation source are coupled into the laser medium along the optical axis of the laser cavity by means of fiber launching means emitting the pulsed excitation beams from the laser diode array with a peak pulse power of at least 400W become

The invention has the particular advantage over the prior art that a solid-state laser system is provided which can be produced by means of conventional, commercially available components. It has surprisingly been found that, in spite of the simple construction, very high pulse energies can be achieved. By using the laser diode array, good match of the wavelength of the excitation beams with the absorption of the laser active material can be achieved. The longitudinal pump configuration ensures good superposition of the excitation beams and the generated laser radiation, resulting in good beam profile and high efficiency. Due to the pulsed excitation, the one or more diodes (s) of the laser diode array can be operated with higher currents and higher output powers since the average thermal stress is greatly reduced. With the proposed solid-state laser system, similarly high output energies are achieved in this way as with lamp-pumped laser systems, but with a much smaller energy requirement and with less effort for the cooling. About that In addition, the generated laser radiation has a beam quality as can not be achieved with lamp-pumped laser systems of the same output energy.

By means of the selected pump arrangement, a good adaptation of the pumped volume to the mode volume of the laser radiation generated is achieved. It can be pumped very high above the lasing threshold so that losses in the resonator are minimized and almost the theoretically quantum efficiency limit is reached. The low ratio of the pulse width to the pulse interval ("duty cycle") results in spite of high pump pulse energies a moderate average power and a correspondingly low temperature increase and phase disturbance in the laser material.

The proposed pulsed longitudinal excitation also allows, especially in a rod-shaped design of the laser medium, that due to a completely coolable outer sheath of the rod-shaped laser medium, a uniform temperature distribution can be generated in the laser medium. By heating and / or cooling a laser rod holder, the strength of thermal lens effects and depolarization can be varied and adjusted. Furthermore, the cross-sectional area of the laser medium used can be varied in relation to the pumped surface in order to vary and adjust thermal lens effects and depolarization.

The fiber coupling device leads to a homogenization of the excitation radiation and to a spatial separation of excitation source and solid-state laser crystal, so that the thermal load is reduced. In addition, the solid-state laser is mechanically decoupled from the excitation source and can be easily moved as a compact unit.

An expedient embodiment of the invention provides that the laser diode arrangement comprises one or more broad area multimode laser diode chips, which has the advantage of a high emitted power with a relatively low cost and a high lifetime of about 100,000 This results in a solid-state laser system with a relatively low cost and a long service life, which is a great advantage in the area of material processing where the processing systems are often used 24 hours a day known lamp-pumped laser systems must be replaced after a few hundred hours and lead to expensive interruptions in production.

In an advantageous embodiment of the invention, it is provided that the laser diode arrangement comprises a laser diode array with a plurality of wide-band laser diodes, whereby a high power can be achieved, which can be further increased by means of parallel connection of several broad-band emitters. The beam quality is higher than that of the wide-range multimode laser diode chips. As a result, even higher efficiencies can be achieved than with the wide-range multimode laser diode chips.

In a preferred embodiment of the invention it is provided that the laser diode array has a laser diode chip stack. As a result, the excitation powers achieved with the wide-range multimode laser diode chips and the laser diode arrays can be further increased by using stacked arrays.

In one embodiment of the invention, a beam shaping device may be provided for shaping a transverse light distribution of the pulsed excitation beams during longitudinal excitation of the laser medium so that the pulsed excitation beams have a power density of at least 50 kW / cm ² at a far field divergence angle of less than 0.6 rad exhibit. As a result, a homogenization of the pulsed excitation beams is achieved. Beamforming is more efficient than fiber coupling. On a coupling fiber can be dispensed with, and there is a cost reduction while avoiding coupling losses in the fiber.

In order to increase the output energy, an advantageous development of the invention provides that pulsed excitation beams having a pulse peak power of at least 1 kW, preferably of at least 2 kW, can be generated with the laser diode arrangement. This serves to achieve even higher output energies and powers.

An advantageous embodiment of the invention provides that the laser-active material is a material from the following group: garnets such as Nd: YAG, Nd: GSAG, Nd: YGG, Yb: YAG, Yb: GSAG, Yb: YGG, vanadate and Nd: GdVO ₄ , Nd: YVO ₄ , Yb: GdVO ₄ , Yb: YVO ₄ , double tungstate such as Nd: KGd (WO ₄ ) ₂₎ Nd: NaGd (WO ₄ ) 2, Nd: KLa (WO ₄ ) ₂ , Yb: KGd (WO ₄ ) ₂ , Yb: NaGd (WO ₄ ) ₂₎ Yb: KLa (WO ₄ ) ₂ and Nd, Er or Yb doped crystals, glasses or ceramics. It is advantageous in one embodiment of the invention that the laser-active material is injection-seeded Nd: GSAG or injection-treated Nd: YGG.

The various materials for the laser medium each have individual properties, some of which are explained in more detail below in the following. Nd: YAG is a standard material for solid state lasers with high efficiency, good heat conduction and high mechanical stability (hardness 8). Nd doped vanadates have very high cross sections and can be even more efficient. Yb doped materials and tungstates have a broadband emission, are thus tunable in their wavelength and are particularly suitable for generating short pulses by mode-locking. In conjunction with Yb-doped garnets, the advantage is very long lifetimes (instead of 200 μs for Nd: YAG) of about 1 ms, which leads to particularly high pulse energies, even in QS mode. The emission of Er is in the eye safe wavelength range. Glasses and ceramics represent flexibility in the shape of the laser medium, lower material costs and wider tunability (glass). Larger laser media can be realized than with crystals.

In an expedient development of the invention, an active or a passive additional Q-switch is provided, so that a Q-switch operation can be performed, whereby a higher peak power, shorter pulses can be achieved. For example, the energy of 50 individual spikes (pulses), each with about 1 μs pulse width in a single giant pulse with only 20 ns pulse width.

The output power and the efficiency of the solid-state laser system are improved in a development of the invention in that a bilateral excitation configuration for the longitudinal excitation of the laser medium is formed.

Appropriately, it is provided in a further development of the invention that the laser medium comprises a multi-rod system, whereby an increase in the active crystal length is achieved, resulting in a higher output power and energy. Furthermore, the thermal load similar to the fiber laser can be reduced. In a preferred embodiment of the invention, a longitudinally pumped MOPA (Master Oscillator Power Amplifier) system is formed comprising a laser oscillator and one or more laser amplifiers. The advantage of the MOPA system is that Q-switching and frequency stabilization are achieved by means of a seed in a master laser with diffraction-limited beam quality at low pumping and output energies. When the output energy increases, the pulse duration, the frequency stability and the beam quality are maintained by means of a downstream amplifier, to which the main part of the pump / excitation power is omitted.

In an expedient development of the invention, it is provided that for the pulsed excitation beams, the diffraction factor M ² > 10 and the beam quality K = l / M ² <0.1, and that for an output beam, the diffraction factor M ² <3 and the beam quality K = l / M> 0.3. An advantageous embodiment of the invention can provide that for the pulsed excitation beams, the diffraction factor M ² > 50 and / or the beam quality K = l / M ² <0.02, and that for an output beam, the diffraction factor M ² <2 and the beam quality K = l / M ² > 0.5. In this way, it is achieved that the beam quality of the output beam is substantially improved with respect to the beam quality of the excitation beams.

In the method for operating the solid-state laser system is provided in an expedient embodiment of the invention that pulsed excitation beams for excitation periods of about 10 microseconds to about 10 ms are generated with the laser diode array. In this way it is possible to adapt to different applications for the solid-state laser system. It can be provided that the excitation periods are matched to the lifetime of the active ion.

In connection with the further dependent claims for the method for operating the solid-state laser system, the advantages mentioned in connection with the associated features in the dependent claims of the solid-state laser system result accordingly. Description of preferred embodiments of the invention

The invention is explained below with reference to embodiments with reference to a drawing. 1 is a schematic representation of a solid-state laser system in which a laser medium formed in the form of a rod is excited by means of pulsed excitation beams, which are generated by a laser diode arrangement, wherein no additional Q-switch is provided;

Fig. 2 is a schematic representation of a solid-state laser system in which a laser medium formed in the form of a rod is excited by means of pulsed excitation beams which are generated by a laser diode arrangement, an additional Q-switch being provided;

Figure 3 is a schematic representation of a solid-state laser MOPA system having a master oscillator of Figures 1 and 2 and one or more post-amplifiers excited longitudinally by means of pulsed excitation beams generated by a laser diode array.

4 is a graph of laser energy versus pump energy for a Nd: GS AG solid state laser system at a wavelength of 942 nm;

Fig. 5 is a plot of pulse energy versus pump energy for a Nd: YAG solid state laser system at a wavelength of 1064 nm; and

Fig. 6 beam profile and beam quality from a measurement in a longitudinally pulsed excited system.

1 shows a schematic representation of a solid-state laser system in which a laser medium 1 formed in the form of a rod and made of a laser-active material is pulsed

Excitation beams are generated, which are generated by means of a pump or excitation source 2, which comprises for generating the pulsed excitation beams, an arrangement with one or more laser diodes which are operated pulsed. The excitation beams generated in the pump source 2 are collimated and focused by means of an optical component arrangement 3 and then pass through a mirror 4 into a laser resonator 5, where they strike the laser medium 1. The mirror 4 is highly reflective for the laser radiation to be generated and transmitiv for the pulsed excitation beams. About a Auskoppelspiegel 7, the generated laser radiation is coupled out.

2 shows a schematic illustration of a solid-state laser system in which a laser medium 1 formed in the form of a rod is excited by means of pulsed excitation beams which are generated by means of a pump source 2 designed as a laser diode arrangement. In Fig. 2, the same reference numerals as in Fig. 1 are used for the same features. In the laser resonator 5, a Q-switch 6 is furthermore arranged, which is an active or a passive Q-switch.

In one exemplary embodiment, pump pulses having a length of 300 μs and a pulse peak power of 380 W were used with the aid of the pump source. In this way, output energies of 114 mJ were achieved, with the pump source 2 being fiber coupled with a fiber diameter of 600 μm and NA - 0.22.

Using Nd: GSAG for the laser medium 1, an efficiency of 30% was achieved at a wavelength of 942 μm for the longitudinal diode-pumped solid-state laser system (see Fig. 4). Pulse energies of over 30 mJ were measured. The laser active material used has a doping of 0.6%, a diameter of 4 mm and a length of 8 mm.

In another embodiment, the active laser material used in the laser medium 1 was Nd: YAG. In this case, an efficiency of 57% was achieved, the measured pulse output energy was 65 mJ (see Fig. 5). The laser active material used has a doping of 0.6%, a diameter of 4 mm and a length of 8 mm.

3 shows a schematic representation of a solid-state laser MOPA system with a master oscillator according to FIGS. 1 and 2 and a post-amplifier 30, which are excited longitudinally by means of pulsed excitation beams which are generated by a laser diode arrangement. In Fig. 3, the same reference numerals as in Figs. 1 and 2 are used for the same features. The output mirror 7 is followed by an optical isolator 31, which prevents feedback into the laser resonator 5. The post-amplifier 30 is pumped by means of a further pump source 32. Fig. 6 shows a measured beam profile for beams generated by a longitudinally pulsed diode-pumped Nd: Y AG laser where M ² = 1.4. As is apparent from Fig. 6, a Gaussian beam profile is present.

The features of the invention disclosed in the foregoing description, in the claims and in the drawing may be of importance both individually and in any combination for the realization of the invention in its various embodiments.

Claims

claims

1. Solid-state laser system with a longitudinal excitation configuration, the following

Comprising: a laser medium (1) which is arranged in a laser resonator (5) and is formed from a laser-active solid-state material,

an excitation source (2) having a laser diode array configured to generate pulsed excitation beams, and

a fiber coupling device configured to couple the pulsed excitation beams from the excitation source (2) along the optical axis of the laser cavity (5) into the laser medium (1), the laser diode array being adapted to provide the pulsed excitation beams with a peak pulse power of at least 400 W to deliver.

2. Solid-state laser system according to claim 1, characterized g ek enn e z ei ch et, that the laser diode array comprises one or more wide-area multimode laser diode chips ("broad area multimode diodes").

3. Solid-state laser system according to claim 1 or 2, characterized g e k enn z ei chn et, that the laser diode array comprises a laser diode array with a plurality of wide-band laser diodes.

4. Solid-state laser system according to one of the preceding claims, characterized g ek enn e z ei chn e t that the laser diode array comprises a laser diode stack.

5. The solid-state laser system according to claim 1, further characterized by a beam shaping device configured to longitudinally excite the laser medium having a transverse light distribution with pulsed excitation beams of a power density of at least 50 kW / cm ² at a far field divergence angle of less than zero To shape 6 rad.

6. Solid-state laser system according to one of the preceding claims, characterized in that the laser diode arrangement is designed to deliver the pulsed excitation beams with a peak pulse power of at least 1 kW.

7. Solid-state laser system according to one of the preceding claims, characterized in that the laser diode array is designed to emit the pulsed excitation beams with a pulse peak power of at least 2 kW.

8. Solid state laser system according to one of the preceding claims, characterized in that the laser-active material is a material from the following group: garnet such as Nd: YAG, Nd: GSAG, Nd: YGG, Yb: YAG, Yb: GSAG, Yb: YGG, vanadate as Nd: GdVO _4, Nd: YVO _4, Yb: GdVO _4, Yb: YVO _4, double tungstate such as Nd: KGD (WO ₄₎ _2, Nd: NAGD (WO ₄₎ ₂₎ Nd: KLa ( WO ₄ ) ₂ , Yb: KGd (WO ₄ ) ₂ , Yb: NaGd (WO ₄ ) ₂ , Yb: KLa (WO ₄ ) ₂ and Nd, Er or Yb doped crystals, glasses or ceramics.

A solid state laser system according to claim 8, characterized in that the laser active material is injection-seeded Nd: GSAG or injection-processed Nd: YGG.

10. Solid state laser system according to one of the preceding claims, characterized by an active or a passive additional Q-switch (6), so that a Q-switch operation is executable.

11. Solid-state laser system according to one of the preceding claims, characterized in that a bilateral excitation configuration for the longitudinal excitation of the laser medium (1) is formed.

12. Solid-state laser system according to one of the preceding claims, characterized in that the laser medium (1) comprises a multi-rod system.

13. Solid-state laser system according to one of the preceding claims, characterized in that a longitudinally pumped MOPA system (MOPA - "Master Oscillator Power Amplifier") is formed, which comprises a laser oscillator and one or more laser amplifiers.

14. Solid-state laser system according to one of the preceding claims, characterized g ek ennz ei chn et, that for the pulsed excitation beams, the diffraction factor M ² > 10 and for an output beam, the diffraction factor M ² <3.

15. Solid-state laser system according to one of the preceding claims, characterized g ek e nn zei chn et, that for the pulsed excitation beams, the diffraction factor M ² > 50 and for an output beam diffraction factor M ² <2.

16. A method of operating a solid state laser system having a longitudinal excitation configuration comprising a laser medium (1) disposed in a laser cavity (5) and formed from a solid state laser active material, the method comprising:

- Pulsed excitation are generated by an excitation source (2) with a laser diode array, and

- The pulsed excitation beams from the excitation source (2) by means of a fiber coupling means along the optical axis of the laser resonator (5) are coupled into the laser medium (1), wherein the pulsed excitation beams from the laser diode array with a pulse peak power of at least 400 W delivered become.

17. The method of claim 16, wherein the pulsed excitation beams are generated using one or more wide-area multimode laser diode chips in the laser diode array.

18. A method according to claim 16 or 17, characterized in that the pulsed excitation beams are generated using a laser diode array having a plurality of wide-band laser diodes in the laser diode array.

19. The method of claim 16, wherein the pulsed excitation beams are generated using a laser diode chip stack in the laser diode array.

20. The method according to any one of claims 17 to 21, characterized in that by means of a beam shaping device during longirudinal excitation of the laser medium (1) has a transverse light distribution with pulsed excitation beams with a power density of at least 50 kW / cm ² at a far field divergence angle of less than 0, 6 wheels are formed.

21. The method according to any one of claims 16 to 20, characterized in that the pulsed excitation beams are generated with a pulse peak power of at least 1 kW with the laser diode array and then irradiated on the laser medium (1).

22. The method according to any one of claims 16 to 21, characterized in that the pulsed excitation beams are generated with a pulse peak power of at least 2 kW with the laser diode array and then irradiated on the laser medium (1).

23. The method according to any one of claims 16 to 22, characterized in that a material from the following group is used as the laser active material: garnet such as Nd: YAG, NdrGSAG, Nd: YGG, Yb: YAG, Yb: GSAG, Yb: YGG , Vanadate such as Nd: GdVO ₄ , Nd: YVO ₄ , Yb: GdVO ₄ , Yb: YVO ₄ , double tungstate such as Nd: KGd (WO ₄ ) ₂ ,

Nd: NaGd (WO ₄ ) ₂ , Nd: KLa (WO ₄ ) _2j Yb: KGd (WO ₄ ) ₂ , Yb: NaGd (WO ₄ ) ₂ , Yb: KLa (WO ₄ ) ₂ and Nd, Er or Yb doped Crystals, glasses or ceramics.

24. The method according to any one of claims 16 to 23, characterized in that with the laser diode array pulsed excitation beams for Anrevmgsdauern of about

20 μs to about 10 ms are generated.

25. The method according to any one of claims 16 to 24, characterized in that using an active or a passive additional Q-switch (6) a Q-switch operation is performed.

26. The method according to any one of claims 16 to 25, characterized in that the laser medium (1) is excited longitudinally on both sides.

27. The method according to any one of claims 16 to 26, characterized in that as the laser medium (1) a multi-rod system is excited longitudinally.

28. The method according to any one of claims 16 to 27, characterized in that the pulsed excitation beams with a diffraction factor M ² > 10 and output beams with a diffraction factor M ² <3 are generated.

29. The method according to any one of claims 16 to 28, characterized in that the pulsed excitation beams with a diffraction factor M ² > 50 and Ausgangsstralilen with a diffraction factor M ² <2 are generated.

30. The method according to any one of claims 23 to 29, characterized in that as the laser-active material injection-seeded Nd: GSAG or injection-seeded NdrYGG is used