In the past half year, we have improved our narrow linewidth Raman fiber amplifier to 20.7 W and 3.5 MHz linewidth. By external resonant cavity frequency doubling, we have obtained up to 14.5 W CW at 589nm with an optical to optical efficiency of 83% (after an optical isolator and other optics, 17.2 W 1178 nm laser is left to couple to the cavity).
My colleagues will present the work at Photonics West 2009 (LASE 2009, 7195: Fiber Lasers VI: Technology, Systems, and Applications, Post-Deadline Session, Paper 7195-101). Below is the abstract:
20W CW, 4MHz linewidth Raman fiber amplifier with SHG to 589nm
Yan Feng, Luke Taylor, and Domenico Bonaccini Calia
European Southern Observatory, Karl-Schwarzschildstr.2, D-85748 Garching, Germany
Up to 20.7 W CW, 3.5 MHz linewidth, 1178 nm continuous-wave laser has been obtained at ESO laser labs by Raman amplification of a distributed feedback diode laser. The 1178nm laser has a linear polarization-extinction-ratio of 25dB. Frequency doubling with an LBO-based SHG commercial cavity has given 83% conversion efficiency and 14.5W CW at 589nm. The source is suitable to produce mesospheric laser guide stars as reference stars for adaptive optics. The presented narrow-band, high power Raman amplification technique might be used for a large number of different wavelength ranges.