Continuous-wave terahertz generation using photomixers

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 GaAs. Optimizing photomixers for maximum output power requires careful design of the epitaxial growth sequence, and detailed analyses of the radio-frequency (RF) circuitry and of the optical feed. Control of the LTG-GaAs epitaxy leads to material with short photocarrier lifetime and robustness to thermal failure. Key tradeoffs are discussed for optimizing the RF and optical feeds for THz output power. Some 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. Two experiments are described that demonstrate the viability of photomixers for these applications.