Eye-safe picosecond Raman laser

The results of development of a picosecond Nd : YAG laser with SBS and SRS pulse compression are presented. The laser emits single-frequency radiation (one longitudinal cavity mode of a passively Q-switched master oscillator) with a pulse energy of 50 mJ at a pulse duration of about 30 ps and a pulse repetition rate of 100 Hz. The output laser wavelength is 1530 nm. The laser beam quality is close to the diffraction limit ($M^2\le 1.2$). Thermally induced phase distortions introduced into the laser beam by the active elements of laser amplifiers are studied and a method of their compensation is proposed. Using this method, we have developed, fabricated, and successfully tested aspherical optical elements compensating for thermal aberrations of active elements, which has allowed us to decrease the beam divergence and increase the output energy.