Active gas sensing with sub-terahertz waves reflected from a wall

We present active gas sensing with a sub-terahertz (THz) spectrometer. The transmitter and receiver of the system are composed of a photonic-base source and a Schottky barrier detector, respectively, and their arrangement is monostatic. From the intensity of the absorption peak of the received sub-THz signal, the density of the sample gas (N₂O) can be successfully obtained.