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Beam shaping of high-power diode lasers

: Du, K.; Baumann, M.; Luft, A.; Röhner, M.; Traub, M.

European Physical Society -EPS-, Geneva:
Conference on Lasers and Electro-0ptics Europe, CLEO/Europe 2000. Conference digest : Nice Acropolis, Nice, France, 10 - 15 Septembre 2000
Piscataway, NJ: IEEE, 2000
ISBN: 0-7803-6319-1
Conference on Lasers and Electro-Optics Europe (CLEO Europe) <2000, Nice>
Conference Paper
Fraunhofer ILT ()

The main advantages of diode lasers are their small size, long life time, high efficiency and frequency controllability. At the moment the obtainable output power from a typical 200 æm emitter is about 2 W. Typical diode laser bars consists of about 20 emitters and delivers about 40 W The beam quality after fast axis collimation la about M(exp 2) = 3 along the fast axis and 1500 along the slow axis and la extremely asymmetrical. For enabling efficient fiber coupling of diode laser radiation different beam shaping techniques have been developed. The common of all beam shaping techniques is to group the beam into subbeam along the slow direction and to rearrange them along the fast axis. The beam quality along both axes can be matched by a suitable selecting the number of subbeams. For scaling output power multi diode laser bars are used. The simplest arrangement is to stack diode laser bars along the fast axis. In this case thin microchannel coolers are used The achievable filling factor in the fast axis and the beam quality la limited. To minimize the loss in beam quality diode laser bars can be mounted by the side of each other along the slow axis and the radiation of each diode laser bar can be stacked by optical means. The wavelength of mostly used high power diode Iasers la between 780 nm to 1000 nm. Using dichroitic optical components, diode laser beams with different wavelength can be coaxial superpositioned. In this way the power of diode laser system can be scaled with the number of wavelength without loss of beam quality in relation to it of a single diode laser bar. Furthermore, Um radiation of diode lasers is linear polarised with a typical polarisation ratio of 1:10. By using a wave plate and a polarisation beam splitt two diode laser bars can be superpositioned without influence on the beam quality. For applications like printing spatially and temporally controllable intensity profile la required To do this addressable diode laser bars can be used. Developments for such applications have been concentred in increasing redundancy and reducing thermal and etectrical cross talking between neighbouring emitters. In other kind applications such es pumping of slab lasers "top hat" intensity distribution is of essential importance Typical tat field intensity profile has two maxima. At the same time, the output power of emitters can be quite different. Homogeneous intensily distributions can for example be realized by using a planar waveguide. In this paper we will discuss recent results about beam shaping and multiplexing techniques of diode lasers for different applications.