Terahertz Frequency Comb High-Resolution Heterodyne Spectrometer

We demonstrate the advantages of THz frequency combs (FCs) for high-resolution spectroscopy. This benefits from wide spectral coverage and the exact knowledge of the frequency position of each comb component. Heterodyne detection combined with a fast Fourier spectrometer enables rapid and simultaneous measurement of more than 80 FC modes covering a 7.5 GHz bandwidth. A spectrum is obtained in under 20 min yielding a uniform resolution of 70 kHz. This new setup has been validated by recording more than 150 lines of methanol around 723 GHz, and represents a new solution to exploit THz FCs for high-resolution spectroscopy.