Investigation on Signal Acquisition and Data Processing of A Fourier Transform Microwave Spectrometer / 分析化学

ABSTRACT

As one of the most important laboratory tools for the research of quantum chemistry and astrochemistry, a microwave spectrometer can make accurate measurement of molecular spectra arising from rotational transitions. Fourier transform microwave (FTMW) spectrometers, in many cases, require down-conversion mixing plans by using mixers to bring the molecular signal down for A/D sampling, and multiple signal averaging to improve the signal/noise ratio as well. Two detection schemes, homodyne and heterodyne detection modes,were proposed in this project along with two data processing plans, averaging in the time domain and averaging in the frequency domain,to develop efficient,sensitive and accurate detection solutions for molecular rotational spectroscopy. With 0. 5% OCS gas in argon as standard sample, verification experiment was conducted with frequency difference between LO and cavity resonance at 200 MHz and 0.4 MHz. The experimental results indicate that, the heterodyne detection method can provide better sensitivity than the homodyne scheme, but with increased cost for more devices, while the time-domain averaging can obtain much better signal-to-noise ratio than frequency-domain averaging,but with stronger data processing capacity and more time required.