Long-pulse XeCl laser operating under active mode-locking conditions

A long-pulse XeCl laser with a magnetic switch and spark ultraviolet preionization, and pumped by a double discharge was developed. The laser consisted of two identical independently pumped sections placed in a shared 75-cm long external resonator. The active medium was 40-cm long and the beam cross section was 2 × 1 cm. The laser generated pulses over its whole aperture. The half-height and overall durations were respectively 250 and 700 ns, with an energy of up to 25 mJ and an efficiency of 0.3%. It was found that a sudden increase in the radiation divergence took place during the trailing edge of the lasing pulse. This was associated with the completion of the development of an unstable discharge. When an acoustooptic modulator and an aperture stop were placed in the resonator, mode locking of the laser was obtained. There were as many as 60 pulses in a pulse train with an overall duration of up to 300 ns and an individual pulse duration of 150 ps.