Terahertz asynchronous optical sampling spectroscopy with lock-in detection

We demonstrate a terahertz asynchronous optical sampling (THz-ASOPS) spectrometer incorporating a lock-in amplifier. The experimental setup employs a high-voltage pulse generator to drive a photoconductive antenna emitter, generating precisely modulated terahertz pulses that are subsequently detected by a photoconductive antenna detector. The detection system features a two-stage amplification process: initial signal amplification through a low-noise current preamplifier, followed by processing with a digital lock-in amplifier. Experimental characterization demonstrates significant performance enhancements, with a 3-fold improvement in the time-domain peak signal-to-noise ratio and a 5 dB increase in the spectral dynamic range. These results substantiate the effectiveness of the lock-in detection approach in enhancing THz-ASOPS spectroscopic performance.