Abstract

There has been widespread interest in generating ultrashort pulses from broadband solid-state materials. However, until recently, pulses generated from solid-state materials have been limited to the order of picoseconds. Pulse widths obtained by most active/passive mode-locking schemes are limited by the relatively slow relaxation time of the saturable absorber. Here we report results of an experimental demonstration of a new technique for producing high-energy, subpicosecond pulses from a solid-state laser system, namely, active/passive mode-locking using a reverse saturable absorber. This technique has been predicted to produce pulses that are shorter than the relaxation times of either absorber. Our laser configuration is similar to a conventional active/passive mode-locked alexandrite oscillator but has an added reverse-saturable absorber, i.e., a material that exhibits absorption that increases with intensity. The saturable and reverse-saturable absorbers shorten the leading and lagging edges of the pulse, respectively. In addition to the pulse-shortening mechanisms of the two absorbers, our preliminary results show that an additional mechanism, similar to that in coupled-cavity lasers, is present in our system. We have determined that an intracavity reflection effectively couples energy from a 150 ps pulse into the ultrashort pulse. Similar results were obtained with an extracavity reflection. To date, our system has produced streak camera limited pulses (ps) containing several microjoules of energy at a repetition rate of 10 Hz.

© 1990 Optical Society of America