High-Repetition-Rate and High-Beam-Quality Laser Pulses with 1.5MW Peak Power Generation from a Two-Stage Nd:YVO_4 Amplifier

We develop a two-stage end-pumped Nd:YVO_4 amplifier seeded by a passively Q-switched microchip laser. An average output power of 13.5 W with repetition rate up to 7 kHz and pulse duration of \sim1.24 ns is obtained, corresponding to a pump extraction efficiency of 16.1% (19.5% for the second stage) and peak power of \sim 1.5 MW. The beam quality factors at maximum output power are measured to be M_x^2=1.56 and M_y^2=1.48. We introduce an analytical model to estimate gain and beam quality after amplification. This model focuses on the influence of ratio of seed spot radius to pump spot radius when designing an amplifier. Moreover, our experiments reveal that the re-imaging system in the double-pass configuration can be used to enhance the beam quality.