While preliminary proof-of-concept experiments proceeded at Stanford using samples fabricated in France, AFRL scientists initiated an in-house, basic research program to study a lowpressure HVPE growth process at the lab’s Optoelectronic Technology Branch, Hanscom Air Force Base (AFB), Massachusetts (see Figure 1) . This group has since taken the lead in growing thick-layer, orientationpatterned GaAs (OPGaAs), and its laboratory remains the only US facility able to provide this technology for patterned semiconductor device research.³ To spur the practical development of GaAs nonlinear devices, AFRL secured Air Force Dual-Use Science and Technology program sponsorship, initiated the Compact and Rugged Midinfrared Active (CARMA) sensor program, and executed a pair of technology investment agreements with industrial partners Northrop Grumman and BAE Systems.

The goal of the CARMA program is to leverage AFRL expertise and facilities to transition breakthrough OPGaAs technology from academia to industry. Under the agreements, collaborating scientists send MBEgrown templates to the AFRL HVPE facility for thick-layer growth. AFRL then provides the finished samples to Northrop Grumman, BAE Systems, and in-house researchers at the lab’s Electro-Optical Countermeasures Technology Branch for characterization and device demonstration.

Progress to date has been encouraging. Researchers at AFRL’s HVPE facility can readily obtain layer growth up to 1 mm thick, producing devicequality samples for a variety of nonlinear interactions. More significantly, CARMA team members have demonstrated OPO performance in OPGaAs devices. Specifically, BAE Systems obtained an output of nearly 0.5 W at 3.4 and 5.2 μm wavelengths with 20% slope efficiency using a thulium- and holium-doped yttrium lithium fluoride laser as the pump source, and successfully tuned this output over a 0.5 μm range by varying the OPGaAs crystal temperature.⁴ In addition, the Stanford group demonstrated a tuning range of several microns by pumping with a tunable PPLN OPO in addition to temperature tuning.⁵ AFRL has made progress in transitioning the technology to industry. When the CARMA program started, Stanford was the only source for MBE-grown templates; now, BAE Systems successfully grows these templates, has increased template diameter from 2 to 3 in., and plans to launch an industrial-grade HVPE facility in the near future.