Abstract

Using a thermally compensated LiNbO₃ electro-optic modulator, we have recently demonstrated 250 W of Q-switched average power. However, the low surface damage threshold of LiNbO₃ may be a problem at average powers of a kilowatt or greater. KTP is a nonlinear crystal with electro-optic coefficients comparable to DKDP and LiNbO₃¹ and with surface damage thresholds 3-5 times higher than LiNbO₃. KTP is biaxial and must be employed in a dual crystal, thermally compensated switch configuration for average power operation. However, flux grown KTP exhibits optical index inhomogeneities which prevents the complete compensation of the static birefringence even over modest (5 × 5 mm²) aperture sizes. In addition KTP exhibits a photochromic damage effect, resulting in a blackened crystal upon application of an electric field. Recently, improvements in KTP crystal growth have yielded large aperture KTP crystals exhibiting a significantly lower depolarization than conventional flux grown KTP of similar aperture. In addition, by utilizing a simple switching configuration, we have demonstrated that KTP can be pulsed continuously without exhibiting photochromic damage. This combination should allow the straightforward development of a large aperture kilowatt Q-switch.

© 1994 Optical Society of America