LONG TERM STABILITY IN CW-CRDS EXPERIMENTS
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Date
2009
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Ohio State University
Abstract
Allan variance can be used to characterize the slow drift of CW cavity ring-down spectroscopy (CW-CRDS) system, caused by the instability of experimental environments. By including the differential measurement of on- and off-peak decay rates in the system, the drifting of both decay rates can cancel out greatly. A sensitivity of $5.6 \times 10^{-12}$ cm$^{-1}$ during an optimum integration time of 15.4 minutes has been obtained with our CW-CRDS system. This sensitivity corresponds a 3$\sigma$ methane detection limit of 0.3 parts per billion by volume (ppbv) in N$_2$ at 20 torr or 37 parts per trillion by volume (pptv) in N$_2$ at 760 torr measurement pressure, near 1.65 $\mu$m laser wavelength.
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Author Institution: Department of Chemistry, University of Virginia, Charlottesville VA, 22904-4319