New scheme for ultrashort-pulsed Nd3 + :YAG laser operation: a branched cavity, internally seeded regenerative amplifier

The development of a simple and reliable source of 8-psec laser pulses, combining the advantages of regenerative amplifier and antiresonant-ring sources, is reported. Recent methods for reducing the duration of Nd(3+):YAG laser pulses are surveyed, and the operating principle of the present design is explained: the amount of coupling between two Fabry-Perot cavities sharing a common laser element is regulated by rotating a quarter-wave plate on an axis parallel to the laser axis. The main cavity terminates in a 50 percent mirror behind a Q-switch, while the sidearm cavity contains a CS2 intensity attenuator and a 100-percent mirror with contacted dye cell. The 15-20 pulses of the output trains are shown to be of 8-psec duration, 3-per-cm spectral bandwidth, 0.7 time-bandwidth product, and slightly more than 500-microjoule individual energy, thus meeting the requirements for application to the study of evolving structured fluorescence spectra and Raman signals.