High-Resolution Frequency-Domain Terahertz Spectroscopy and its Application to Electron Paramagnetic Resonance

Frequency-domain terahertz (THz) spectroscopy using a continuously tunable photomixer is a powerful analytical technique, offering unique advantages such as high frequency resolution. Here, we report an improved method to increase the spectral resolution using a pair of fiber stretchers. In this method, the amplitude of transmitted THz waves was determined at each frequency by modulating the optical path difference. As a result, the spectral resolution of about 1 MHz was achieved in this study. We applied this technique to frequency-domain electron paramagnetic resonance (EPR) spectroscopy, and successfully observed EPR spectra with a 20-MHz line width.