Abstract

A two-photon absorbing semiconductor inserted in the cavity of a Nd Q-switched mode-locked lasers is shown to act simultaneously as energy limiter and pulse compressor. The latter action is due to self defocusing by the carriers generated during the pulse. With a proper positioning of an intracavity aperture, maximum losses occur at the tail of the pulse, resulting in pulse compression. Extracavity measurements have shown that the compression factor can be as large as 50%. The energy limiting effect ensures optimum operation for the intracavity saturable absorber. As a result, the pulse train is stabilized and stretched out to include at least 100 pulses of nearly equal energy and duration (10 ps for the Nd:YAG laser). The reproducibility of the stabilized pulses is better than 1.5 from shot to shot. Typically, the evolution towards steady state in a fs laser requires about 100 round-trips. With an energy/pulse of 10 J, and at least 100 pulses of identical energy, the new source has unique characteristics for pumping fs dye lasers.

© 1990 Optical Society of America