Evanescent Wave Cavity Ring-Down Spectroscopy: A New Platform For Thin-Film Chemical Sensors

Published

July 30, 2009

Author(s)

A C. Pipino

Abstract

A new optical technique is described that permits extension of cavity ring-down spectroscopy (CRDS) to surfaces, films, and liquids. As in conventional CRDS, the photon lifetime in a low loss optical cavity is utilized to probe optical absorption. Extension to condensed matter is achieved by employing intra-cavity total internal reflection (TIR) to generate an evanescent wave that is especially well suited for thin film chemical sensing. Two general monolithic cavity designs are discussed: 1) a broadband, TIR-ring cavity that employs photon tunneling to excite and monitor cavity modes, and 2) a narrow bandwidth cavity that utilizes a combination of TIR and highly reflective coatings. Following a qualitative description of design features, a beam transfer matrix analysis is given which yields stability criteria and mode properties as a function of cavity length and mirror radius of curvature. A signal-to-noise ratio calculationis given to demonstrate the evaluation of sensitivity.

Citation

SPIE series

Pub Type

Journals

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Keywords

cavity ring-down, chemical sensing, Evanescent waves, films, optical absorption, resonator design

Citation

Pipino, A. (2009), Evanescent Wave Cavity Ring-Down Spectroscopy: A New Platform For Thin-Film Chemical Sensors, SPIE series, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=830647 (Accessed October 17, 2025)