Photomixing-based (sub-)millimeter frequency spectrometer for environmental metabolite detection
Résumé
We present a spectrometer, working in the (sub-)millimeter frequency range for the detection of volatile molecules. Our main objective is to introduce a new analytical detection method dedicated to the soil metabolism. The photomixing frequency synthesizer emits continuous waves with frequencies ranging from 25 to 742 GHz. Thanks to a laser frequency stabilization onto an optical cavity, we achieve 40 kHz linewidth of the synthesized frequency. A thermal stabilization of the cavity ensures frequency repeatability with a relative precision of 2•10^-6 . We achieve coherent homodyne detection independent of generated frequencies. As representative of soil metabolites, acetonitrile is used to assess the instrument. The instrument performances are illustrated by the detection of rotational transitions of acetonitrile vapor in the 164.5 -166.5 GHz range at partial pressures around 1 mbar. We also analyze the instrument sensitivity from the detector noise characteristics. This analysis serves to define the detector limit of the instrument.
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