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Proceedings Paper

Evanescent-wave cavity ring-down spectroscopy for trace water detection
Author(s): Andrew C. R. Pipino; Joseph T. Hodges
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Paper Abstract

We explore the use of evanescent wave cavity ring-down spectroscopy (BW-CRDS) for water detection through a signal-to-noise ratio analysis. Cavity ring-down spectroscopy (CRDS) is an emerging optical absorption technique that employs the mean photon decay time ofa high-finesse optical cavity as the absorption-sensitive observable. EW-CRDS is a novel implementation of CRDS that extends the technique to surfaces, films, and liquids by employing optical cavities which incorporate at least one total-internal-reflection (TIR) mirror. The concomitant evanescent wave is then used to probe the absorption ofan ambient medium at the TIR surface also through a change in the photon decay time. By employing miniature monolithic cavities with ultra-smooth surfaces that are fabricated from ultra-high transmission materials, extreme sub-monolayer detection sensitivity is readily achieved. The detection of water by EW-CRDS with a fused-silica resonator provides an interesting and important application, since the nascent hydroxylated Si02 surface is expected to show a high natural affinity for adsorption ofwater through hydrogen-bonding interactions. Furthermore, in the 13 80 nm spectral region where water absorbs strongly, low-OH-content fused silica has extremely high bulk transmission. These factors potentially provide the basis for a novel water sensor.

Paper Details

Date Published: 26 February 2001
PDF: 11 pages
Proc. SPIE 4205, Advanced Environmental and Chemical Sensing Technology, (26 February 2001); doi: 10.1117/12.417432
Show Author Affiliations
Andrew C. R. Pipino, National Institute of Standards and Technology (United States)
Joseph T. Hodges, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 4205:
Advanced Environmental and Chemical Sensing Technology
Tuan Vo-Dinh; Stephanus Buettgenbach, Editor(s)

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