Efficient totally-passive compact high-repetition-rate picosecond UV source

Summary form only given. Our experiment is performed with a passively Q-switched Nd/sup 3+/,Cr/sup 4+/:YAG microchip laser which delivers 500-ps pulses. To optimize the repetition rate, different pump diodes were tried. The optimum is found with a high-brightness cw laser diode which enables us to obtain a very high repetition rate up to 45 kHz with an average power of 37 mW. For the amplifier, we choose a Nd:YVO/sub 4/ crystal which, because of its high emission cross section, gives a good energy extraction. To decrease thermal effects, we use as gain medium a composite crystal comprising 1-mm-long undoped YVO/sub 4/ bonded to 1%-doped 3-mm-long Nd:YVO/sub 4/. With this composite crystal both efficiency and beam profile quality (nearly gaussian) are optimized.