A method to detect gas based on the Fabry–Pérot cavity by using terahertz frequency-domain spectroscopy

Due to the limitation of the gas volume as well as the optical path, sometimes the absorption peak of the gas is difficult to observe. Here, we present a new gas detection method based on the Fabry–Pérot cavity, which can effectively enhance the absorption peaks of gases by using terahertz frequency-domain spectroscopy. By changing the cavity length, the cavity resonance center frequency and resonance modes can be changed to detect multiple gases or to observe the performance of the same gas in different resonance modes. The enhancement of the absorption peak at 560 GHz for water vapor has been successfully observed, and it is expected to be useful for the detection of various substances.