Frequency Calibration of Terahertz Time-Domain Spectrometer Using Air-Gap Etalon

Although various terahertz (THz) technologies have been rapidly developed in recent years, their metrology standards are yet to be established. We have developed a simple calibration method for the frequency of a THz time-domain spectrometer (TDS) using an optically transparent THz air-gap etalon (OT-TAGE). The OT-TAGE can be used in both the near-infrared (NIR) and THz regions. Therefore, a frequency measurement using THz waves can be directly compared with one using NIR light via the OT-TAGE. In this study, the frequency of a commercial THz-TDS was calibrated by referring to the NIR wavelength was demonstrated. The obtained frequency errors were within ± 3 GHz, with relative uncertainties within 1%.