Diffraction limited output from a CW Nd:YAG MOPA with a fibre phase conjugate SBS mirror

It is well known that powerful solid state lasers suffer from thermal lensing and stress birefringence which reduce their output beam quality. A number of approaches and techniques have been suggested to reduce, suppress or compensate these two effects. Of these the most successful (high quality diffraction limited output beam) is based on phase conjugation in a master oscillator/power amplifier (MOPA) configuration. So far this technique has been used in single pulse or pulse-periodic regimes only. Following the recent realization, by the authors, of efficient self-phase conjugation via SBS of CW laser radiation in an optical fibre, in this communication we report the first demonstration of beam clean up in a CW Nd:YAG MOPA system based on this technique