Directly diode-pumped, short pulse CPA laser delivering energies in the 10 to 50 mJ range

Summary form only given. Today, injection of high-energy short-pulse laser chains requires an energy of several tens of millijoules and a somehow broad spectrum. Several methods have been proposed to achieve this goal, including optical parametric chirped pulse amplification (CPA) or regenerative amplification in Ti:sapphire. In both cases, a high energy pump laser is required at wavelengths where laser diodes can not be used. As a result, the main limitation is the available pumping energy. We demonstrate an alternative method based on a directly diode-pumped Nd:phosphate glass rod where the emphasis is put on spectrum control and extraction efficiency in order to successfully amplify sub-picosecond laser pulses to the 10-50 mJ level of energy. The laser chain, based on the CPA technique, is of typical composition. We use a commercial directly diode pumped short pulse oscillator delivering 100 MHz laser pulses with a 8 nm large spectrum where mode locking is achieved by a SESAM. Then the laser pulses are temporally stretched to 800 ps in a two-lens stretcher. The pulse to be amplified is selected by a Pockels cell and sent to the amplifier where it undergoes regenerative amplification by a factor of 10/sup 6/ at a 1 Hz repetition rate, before it is released and sent to the compressor.