Abstract

Picosecond generation by a Nd:YAG self- filtering unstable resonator (SPUR) has been extensively tested. Gobbi and Reali^1,2 introduced the SPUR as an improved resonant cavity for high gain laser systems. They showed that it has substantially better focusability, higher transverse mode selectivity, and good power extraction when compared to standard resonant cavities with the same gain medium. We report here the results of the investigation on short pulse generation by a modified SFUR.³ The system was assembled in a 10- Hz twin oscillator-amplifier configuration (Fig. 1) and was operated in two different ways, passive-active and Q-switched-active mode-locking, depending on the desired output requirements. In both cases polarization coupling was used to optimize optical beam quality, which was measured to be quasi-Gaussian in shape as predicted by theory. Intracavity sapphire etalons were used in the passive-active mode-locking to obtain time durations between 50 and 200 ps with pulse energies up to 200 mJ in a single cavity dumped pulse and amplitude stability of ±5%. Q-switch-active mode-locking gave 300 mJ in a single cavity- dumped 300-ps pulse, and the same ±5% amplitude stability was obtained by synchronizing the Q-switching on with a certain fixed phase of the acoustooptic modulator. A SNR performance of better than 10² was obtained in the cavity dumping operation. A compacted SH-TH BBO based generator produced over 120 and 50 mJ of second and third harmonic, respectively. The system was tested and qualified to be airborne. (Poster paper) CWF2 Fig. 1 Passive-active mode-locking SPUR schematic.

© 1990 Optical Society of America