Nd~(3+):YAG PUMPED DOUBLE-PASS EXTRA-CAVITY BARIUM NITRATE RAMAN LASER DOUBLED IN LBO NONLINEAR CRYSTAL

摘要

A Barium Nitrate Raman laser pumped by Q-switched Nd:YAG fundamental radiation has been developed. Narrow linewidth and high conversion efficiency of the pump radiation is observed. Compared with an intra-cavity Raman laser, the extra-cavity option is the more versatile solution, as the pump laser need not be modified. The Raman laser configuration was used in preference to the single pass option due to higher efficiency reduced threshold and output beam divergence obtained. While the extra-cavity barium nitrate Raman laser is not tunable it is a narrow band, efficient pulsed source at 1197nm. The main limitations of this laser have been identified as the shot to shot output stability and high beam divergence when used with a pump beam diameter of 7 mm. High beam divergence complicates collimation and therefore subsequent frequency doubling of the Raman output beam due to the low acceptance angle values for most modern nonlinear crystals. Beam quality of the Raman laser is sensitive to alignment of optics in the Raman laser cavity and quality of the Raman medium. Non uniformity in the Barium Nitrate crystal is thought to result in hotspots in the output beam. Precise optical alignment of the Raman laser is necessary if beam output quality is to be maintained.