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Efficient Raman frequency conversion of high-power fiber lasers in diamond

 
: Williams, R.J.; Nold, Johannes; Strecker, M.; Kitzler, O.; McKay, A.; Schreiber, Thomas; Mildren, R.P.

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Laser & photonics reviews 9 (2015), No.4, pp.405-411
ISSN: 1863-8880
ISSN: 1863-8899
English
Journal Article
Fraunhofer IOF ()

Abstract
We report high-power frequency conversion of a Yb-doped fiber laser using a double-pass pumped external-cavity diamond Raman oscillator. Pumping with circular polarization is shown to be efficient while facilitating high-power optical isolation between the pump and Raman laser. We achieved continuous-wave average power of 154W with a conversion efficiency of 50.5% limited by backward-amplified light in the fiber laser. In order to prove further scalability, we achieved a maximum steady-state Raman-shifted output of 381W with 61% conversion efficiency and excellent beam quality using 10ms pump pulses, approximately a thousand times longer than the transient thermal time-constant. No power saturation or degradation in beam quality is observed. The results challenge the present understanding of heat deposition in Raman crystals and foreshadow prospects for reduced thermal effects in diamond than originally anticipated. We also report the first experimental evidence for stimulated Brillouin scattering in diamond. Diamond is used for Raman beam conversion of a 700 W Yb fiber laser, achieving record conversion efficiency (>60%) and output power (380 W). High beam quality and efficient conversion at high powers-in stark contrast to predictions for the thermal lens and cavity stability-challenge the current understanding of heat deposition in diamond Raman lasers. Experimental evidence for stimulated Brillouin scattering in diamond is reported.

: http://publica.fraunhofer.de/documents/N-356350.html