The Thz Wave Time-domain Spectroscopy Detection Of Organic Gases

THz wave is electromagnetic wave whose frequency is between 0.1 THz and 10THz. This spectrum which covers pure rotational spectra of many gases belongs to far infrared and sub-millimeter wave.Pure rotational spectra of three kinds of organic gases (methanol, ethanol and acetone) had been measured by THz-TDS respectively. THz waves were both generated and detected by photoconductive antenna. The frequency range of our THz system is from 0.1 up to about 3 THz. Gas samples were filled in a 5 cm long glass cell with 2 mm-thick polyethylene windows, which was placed in the THz waves path. The absorption spectra of the gases at the THz range were measured and compared with that of N₂ which is as the reference.Acetone gas has a wide absorption band under 1.5 THz and methanol gas has a series of absorption lines at the range from 0.5 THz to 3 THz. The absorption peaks of acetone and methanol gas were at 0.56 THz and 2.03 THz respectively. The absorption coefficient of the 2.03 THz line was about 0.3 cm^-1. However, according to our experimental results, ethanol gas showed no obvious absorption.According to the experimental results of this thesis, different gases can be identified using THz-TDS to detect their characteristic absorption spectra. This technology has a great application prospect on the gas-identification, environmental monitoring and protecting areas.This research was conducted at Center Research Lab of Hamamatsu Photonics K.K. in Japan.