Phase conjugation for high-power solid state lasers with repetition rates in the kHz range

Abstract

Industrial applications require lasers with high beam quality combined with kHz repetition rates. The average output power peak power and the repetition rate should be variable. Using phase conjugation based on stimulated Brillouin scattering (SBS) the beam quality of such high power solid state lasers can be improved significantly. High average power MOPA systems in double-pass configurations with SBS-mirror and high repetition rates were developed. To simplify multi-amplifier systems, Nd:YALO as active material was used to avoid depolarization of the amplified beams. With two amplifiers, average output powers of more than 200 Watts with high beam quality were realized. The system works with an average repetition rate up to 3 kHz and pulse widths of up to 200 ns. Peak and average output power can be varied over a wide range. Second harmonic generation with such a system leads to an average output power of 50 W at 540 nm wavelength with a conversion efficiency of 50 percent. Using SBS in glass fibers the power threshold for phase conjugation can be reduced and therefore first experiments with a continuously pumped Q-switched MOPA-system with SBS- mirror were realized.