Periodic variations of sum-frequency output are observed in upconversion of 10.6 µm radiation from a CO2 laser in a proustite crystal pumped by a Nd:YAG laser beam and concluded to be caused by multiple reflection of infrared wave which occurs inside the nonlinear crystal.

A new structure GaAs power FET was designed and fabricated for high output power with sufficiently high efficiency. The undoped surface layer was introduced to achieve simultaneous increase in the maximum channel current (Imax) and the gate drain breakdown voltage (BVgd) under the large signal RF conditions. In addition the step-recessed gate structure was adopted and optimized to attain a high breakdown voltage and a high linear gain by using the two dimensional device simulator. A high fmax of 65 GHz was obtained at the "class-A" mode bias point, with the 0.55 µm gate length. The maximum fmax of 91 GHz was obtained. The test device feasibility was tested at 12 GHz and the output power/efficiency characteristics of 4.0 W/40.1% with the gain of 9.2 dB have been achieved in the "class-A" mode operation for a single chip (gate width8.18 mm). To the authors' knowledge, these RF power performances with high linear gain are the best data at 12 GHz.

Two-dimensional acceptance angles of a proustite upconverter operating in several type I phase-match conditions are measured and compared with theoretical ones. They agree reasonably well with each other.