Orientation-Patterned Semiconductor Crystals with Low Insertion Loss and High Resistance to Laser Damage

The Air Force needs tunable laser systems with high average power in the mid-infrared region of the spectrum for military applications including defense against heat-seeking missiles. Currently-fielded laser systems, based on nonlinear frequency conversion in periodically poled lithium niobate (PPLN), have limited optical power at wavelengths between 4 m and 5 m because of intrinsic absorption in the nonlinear optical material. Systems under development, based on orientation-patterned gallium arsenide (OP-GaAs), do not suffer from this transparency problem, but their output power is still limited by optical damage. PSI, in collaboration with its academic partner, University of Maryland, Baltimore County, and BAE Systems proposes to use a novel fabrication process to produce textured surfaces on OP-GaAs that have the low infrared reflectivity needed for defense applications, along with a higher laser damage threshold than with currently-available nonlinear optical crystals. During Phase I we proved the feasibility of our approach by developing a wafer-scale process for producing the proposed low-reflectivity surface and making laser damage threshold measurements. During Phase II we will prove the practicality of our approach by fabricating OP-GaAs devices incorporating these design improvements and delivering them to the Air Force for testing under high-average-power conditions.