Continuous-wave terahertz spectrometer without active phase modulation (Conference Presentation)

We present a novel system architecture for coherent cw THz spectrometers. The system features 2.5 THz bandwidth with an acquisition rate of 58 Hz and provides full phase information without active phase modulation. We achieve passive amplitude and phase modulation at a fixed intermediate frequency by using a fast sweeping laser in combination with a static optical fiber delay: By heterodyning the incoming THz signal with the frequency-shifted optical beatnote on a photomixing receiver, we can extract amplitude and phase of the signal with a lock-in detector. To the best of our knowledge, this is the fastest coherent cw THz system demonstrated so far.