Photomixers for Continuous-Wave Terahertz Radiation

Abstract

Optical heterodyne conversion, or photomixing, is a frequency-agile technique that generates continuous-wave radiation at THz frequencies using thin films of low-temperature-grown (LTG) GaAs. Optimizing photomixers for maximum output power requires careful design of the epitaxial growth sequence, and detailed analyses of the RF circuitry and of the optical feed. Control of the LTG GaAs epitaxy leads to a material with short photocarrier lifetime and robustness to thermal failure. Key aspects of the photocarrier lifetime, quantum efficiency, and thermal performance are described for the photomixer. Trade-offs for optimizing the RF and optical design for THz output power are discussed. Promising applications for photomixers include local oscillators for THz heterodyne detectors based on superconductors, and high-resolution spectrometers useful for rotational spectroscopy of airborne molecules.