Horizontal gradient freeze growth of AgGaGeS 4 and AgGaGe 5Se 12

Abstract

AgGaGeS 4 and AgGaGe 5Se 12 are promising new nonlinear optical crystals for frequency-shifting 1-μm solid state lasers into the mid-infrared (2–12 μm) spectral range. The quaternary compounds were synthesized by vapor transport in sealed ampoules from high purity elemental starting materials, and crystals were grown by the horizontal gradient freeze technique in transparent furnaces. AgGaGe 5Se 12 exhibited incongruent melting behavior, and small optical samples extracted from an as-grown polycrystalline boule had high scattering losses. AgGaGeS 4 growth was far more favorable, resulting in a crack-free single crystal measuring 19 mm in diameter and >80 mm 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.