Investigation of birefringence uniformity of mid-IR nonlinear optical crystals

An investigation of the birefringence uniformity of mid-IR non-linear optical crystals has been conducted in an effort to improve the performance of crystals used in OPO converters. This paper discusses the development of an imaging polarimeter operating at 2 μm for the characterization of birefringence uniformity of nonlinear optical crystals for use in mid-IR generation. The spatial distribution of optical in-homogeneity is directly revealed in terms of optical rotation in the polarimeter. The root cause for the optical rotation observed in the polarimeter is discussed in terms of fluctuations in the material birefringence, or excess birefringence. Excess birefringence on the order of un=10 -4 are measured in samples exhibiting the rare occurrence of low birefringence uniformity in our mid-IR nonlinear optical crystals.