Application of highly sensitive millimeter-wave cavity spectrometer based on orotron for gas analysis

Highly sensitive millimeter-wave spectrometer based on tunable coherent source-orotron is proposed for detection of molecular compounds in the air and water vapor by observation of their rotational spectra in frequency region 90-150 GHz. High sensitivity of measurements (2-3) x 10(-10) cm(-1) which gives the detection limit better than 1 ppm for wide class of molecules is achieved by the placement of investigated gas into a high quality (Q approximate to 10(4)) orotron Fabry-Perot resonator. The absorption signal is measured simply from variation of orotron current in the collector circuit. The narrow spectral width of orotron radiation (15 kHz) provides Doppler resolution of spectral lines and high selectivity of analysis respectively without any locking by external frequency standard. The spectrometer has relatively simple operation principles taking account its universality. At the first step four compounds, namely methanol, acetone, carbonyl sulfide and carbon monoxide, have been measured in mixtures with water vapor or air. (C) 1997 Elsevier Science B.V.