Growth of new quaternary nonlinear optical crystals for 1-micron-pumped mid-IR generation

Abstract

Crystal growth of two new quaternary crystals, AgGaGeS 4 and AgGaGe 5 Se 12 , was performed in order to evaluate the usefulness of these materials for nonlinear optical frequency conversion of one-micron solid state lasers into the mid-infrared spectral region beyond 4 microns. Each compound was synthesized by vapor transport in sealed ampoules from high purity elemental starting materials, and crystals were grown by the gradient freeze technique in horizontal transparent furnaces. AgGaGe 5 Se 12 exhibited incongruent melting behavior, and small optical samples extracted from an as-grown polycrystalline boule had high scattering losses. AgGaGeS 4 crystal growth proved to be far more favorable, resulting in a crack-free single crystal measuring 19mm in diameter and >80mm in length with as-grown 2.05-μm absorption losses < 0.05 cm -1 . The measured laser damage threshold of an uncoated AgGaGeS 4 crystal at 2.05 μm was 1.1 J/cm 2 , and room-temperature measurements of thermal diffusivity, heat capacity, and thermal conductivity yielded values of 0.224 mm 2 /s, 0.448 J/g/K, and 0.399 W/mK respectively for the sulfide. The growth and properties of AgGaGeS 4 , despite being a quaternary compound with complex phase equilibria, appear indeed to be promising for shifting Nd-laser output directly into the mid-IR.