| Nonlinear optical frequency conversion is an effective technique for generating infrared (IR) and terahertz (THz) wavelengths not readily available from existing laser sources. Traditional birefringent materials such as LiNbO 3 are often used to generate wavelengths where gaps exist, but are unsuitable in the mid-IR and THz regions as these materials are often opaque in these regions. As an alternative, the III-V semiconductors GaAs and GaP have been employed for frequency conversion in these regions using the quasi-phase-matching (QPM) method to overcome the materials' lack of birefringence. Here, QPM OP-GaAs templates were successfully produced using wafer fusion, mechanical polishing, selective wet etching, standard photolithography, wet etching to create the opposite crystal orientation, and subsequently thick hydride vapor phase epitaxy (HVPE) GaAs film overgrowth at the Air Force Research Laboratory (AFRL). Efficiency as high as 1.9%, a record to the best of my knowledge, was obtained for frequency doubling of a CO2 laser using one of these QPM OP-GaAs devices. Unfortunately, GaAs suffers from strong two-photon absorption below 1.7 mum, making it inefficient when pumped with a source less than or equal to this wavelength. On the other hand, GaP has lower two-photon absorption below 1.1 mum, higher thermal conductivity, and a wider transparency range as compared to GaAs. Therefore, OP-GaP is suitable for nonlinear optical applications in the mid-IR and THz that use commercially available pump lasers in the 1.06- to 1.55-mum wavelength range. Here, OP-GaP templates were demonstrated for the first time using wafer fusion and several of the templates were successfully overgrown with thick HVPE GaP layers. Furthermore, the template fabrication process is robust and scalable to commercial production. |
