Abstract

In recent years there has been a steadily growing interest in both fixed-frequency and tunable mid-infrared lasers emitting in the 3–5 micron spectral band. The successful development of high-figure-of-merit non-linear optical materials such as AgGaSe₂ and ZnGeP₂, with wide transparency and phase-matching ranges in the infrared, has been largely responsible for the advances that have been demonstrated. Each material suffers from its own limitations, however. ZnGeP₂, despite its large nonlinear optical coefficient, exhibits a large defect-related absorption band which tails out beyond 2μm, thereby degrading the performance of optical parametric oscillators pumped by holmium lasers. AgGaSe₂ also exhibits an anomalous absorption band around 2μm which, due to the material’s low thermal conductivity (30× lower than ZnGeP₂), can introduce severe thermal lensing when pumping at high average powers. While improvements in crystal growth and post-growth annealing continue to lower the residual losses in these materials, it is important to search for new materials with higher nonlinearities and/or lower infrared losses.

© 1995 Optical Society of America