Abstract

New crystals of KTP and beta-barium-borate (BBO) have been recently identified as highly efficient crystals with nonlinear coefficients of 15 and 4.6 times the KDP, respectively. The BBO crystal has the advantages of very wide temperature acceptance width and high damage threshold.¹ However, due to the rather large walk-off angle (~50 mrad) of this crystal, a good quality pump is usually required for high conversion efficiency. We present the first direct comparison of the SHG efficiency of a YAG laser (1064 nm) by using KTP, BBO, and CD* A with crystal lengths of 3, 7, and 25 mm, respectively. The phenomena occurring in loci of nonlinear phase-matching directions for these three crystals were observed and compared. We found that, particularly for BBO crystal, the SHG efficiency is a strongly decreasing function of the divergence of the pump field. Data have been collected for cases employing conventional spherical imaging and also asymmetric imaging using both cylinder lenses and anamorphic prisms. Improved efficiency was obtained by asymmetric focusing. Data were compared with a computer model.

© 1987 Optical Society of America