We present a portable spectrometer that uses the frequency-stabilized cavity ring-down spectroscopy technique to realize high-precision measurements of trace water vapor concentration. Measuring one of the strongest rovibrational transitions in the 1 + 3 water vapor combination band near ~ =7181:156 cm 1, we compare spectroscopic and thermodynamic determinations of tracewater vapor in N2, and nd systematic di erences attributable to water vapor background e ects and/or uncertainties in line intensities. We also compare the frequency-stabilized ring-down method with other cavity ring-down approaches that are based on unstabilized probe lasers and unstabilized ring-down cavities. We show that for the determination of water vapor concentration, thefrequency-stabilized cavity ring-down method has the minimum measurement uncertainty of these three techniques. The minimum noise-equivalent absorption coefficient of the spectrometer was 1:2 10 10 cm 1 Hz 1=2.
Citation: Applied Physics B
Pub Type: Journals
cavity ring down, hygrometer, laser spectroscopy, water vapor