Ultra-sensitive detection of coherent and incoherent terahertz radiation at room-temperature with a plasmonic photomixer-based heterodyne receiver

Heterodyne receivers based on plasmonic photomixers have demonstrated high sensitivity terahertz detection with broad terahertz bandwidth and high spectral resolution. We report the ultra-sensitive performance of a room-temperature terahertz receiver based on a plasmonic photomixer, with broadband tunability up to 5 THz, for the detection of faint incoherent and coherent signals, such as those constituting the majority of cosmic radiation. By modulating the received signal and implementing spectral digital lock-in detection technique, the background noise is significantly reduced, and quantum-level sensitivity levels are achieved. By implementing an optical phase-locked loop, the terahertz beat frequency is stabilized between the lasers, ensuring a narrow IF linewidth for high spectral resolution. Finally, via means of a piezo-electric nano-positioning stage, mechanical stabilization between the optical LO and the photomixer active region is maintained, offering long-term stability with longer than 1-hour Allan time for high-sensitivity astrophysics observations.