SBIR Phase I:Large Aperture, Periodically-Structured Gallium Arsenide for Infrared and THz Wavelength Conversion

This Small Business Innovation Research (SBIR) Phase I project will investigate novel optical bonding techniques to produce periodically-structured gallium arsenide (GaAs) nonlinear crystals. High-power, widely-tunable infrared sources are needed for applications in chemical-biological sensing, climate monitoring, medical diagnostics, multispectral imaging, laser spectroscopy, terahertz spectroscopy and imaging, and infrared countermeasures. Such infrared sources are typically created by wavelength conversion of a high-power source using a nonlinear crystal. Existing crystals for infrared bands are limited in their performance, compromising all the applications above. GaAs is recognized as a superior nonlinear material compared to other crystals, but it cannot be birefringently phase-matched. To enable wavelength conversion, GaAs crystals must be fabricated into layers of alternating crystal domains (quasi-phase-matching, QPM). While these structures have now been fabricated using epitaxial growth techniques - validating the usefulness of QPM with GaAs - those methods will likely never produce the cm-size optical apertures required for high-power applications. Fundamental studies of interfacial losses for bonded GaAs will be undertaken, leading to demonstrations of multi-layer, high-strength, large-aperture structures suitable for high-power applications. The results of this research will be detailed physical understanding of the interface physics, opto-mechanical characterization of the fabricated structures, and important guidance for wafer-based commercial production. The broader impact/commercial potential of this project is to provide large aperture GaAs nonlinear crystals that have scientific, commercial, and societal merit in two different ways. First, the novel bonding processes that will be investigated are the first steps to functional large-aperture wavelength conversion devices in QPM GaAs. Such layered material structures are generally referred to as 'engineered nonlinear materials', and Periodically-Poled Lithium Niobate (PPLN) is the most well-known example. PPLN has supplanted most other nonlinear materials in its infrared wavelength conversion region (~2-5um), and has initiated a multi-field-of-use market that now includes numerous engineered structures. Periodically-structured GaAs will extend these markets for engineered nonlinear materials across the entire infrared region (~2-14um). Second, the production of engineered infrared materials will enable new scientific investigations in spectral regions that are currently difficult to access, require higher power, or are otherwise commercially unfeasible or impractical. Examples include multispectral infrared systems to protect our military forces and homeland from chemical and biological threats, terahertz systems that can interrogate hidden structures (and humans) more safely than x-rays and can detect weapons and explosives, fundamental scientific infrared spectroscopic studies, and improved medical equipment and diagnostic techniques.