Frequency calibration of THz time-domain spectrometers using an etalon

We present an etalon-based method of calibrating the frequency of THz time-domain spectrometers (TDS). The method utilizes the etalon effect produced by multiple reflections in non-absorbing wafers or in narrow air-gaps. The technique provides frequency calibration across the measurement band with uncertainties comparable with the typical THz TDS resolution.