Spectral lock-in amplifier for plasmonic heterodyne terahertz receivers

Lock-in amplifiers enhance the signal-to-noise ratio (SNR) by suppressing background noise. Conventional designs, however, lose frequency information, limiting their use in spectrometry. We introduce a spectral lock-in amplifier that preserves spectral data while reducing noise. Frequency components are extracted, demodulated using a reference signal, and low-pass filtered for further noise suppression. Applied to a plasmonic heterodyne terahertz receiver, it achieves a 10 dB noise reduction per decade of integration time. This technique is valuable for broadband spectral studies, including astronomy and gas sensing.