Generation of trains of ultrashort (100-ps) pulses continuously tunable over the interval 307.6–308.6 nm by a long-pulse XeCl laser

A long-pulse XeCl laser has been developed which is capable of generating, under conditions of active mode locking, trains of ultrashort pulses 100 ps long which are continuously tunable over the interval 307.6–308.6 nm. The number of pulses in a train ranges up to 60. With an intracavity Fabry–Perot etalon, pulses which are approximately spectrally bounded are obtained. The length of the ultrashort pulses has been studied as a function of the length of the laser cavity and the order of the pulse in the train. There is a significant increase in the length of the ultrashort pulses in comparison with the minimum length as the cavity length is varied by more than 1 mm. The minimum length attainable (100 ps) is not determined by the lifetime of the population inversion in the laser (0.5 μs). It is instead determined by other factors, most significantly the time variation of the pump. Ways to further improve the stability and reduce the length of the ultrashort pulses generated by long-pulse XeCl lasers (τ>0.5 μs) under mode-locking conditions are discussed. The operation of such lasers with mode locking with an attached nonlinear cavity is analyzed. Numerical calculations show that pulses shorter than 10 ps can be achieved in this case.