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22 January 1999 Evanescent wave cavity ring-down spectroscopy for ultrasensitive chemical detection
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A new technology will be described which extends the cavity ring-down optical absorption technique to condensed matter by using a miniature, high-finesse, monolithic, total- internal-reflection-ring resonator. Evanescent waves that are generated by total-internal reflection permit input and output coupling by photon tunneling and probe the presence of absorbing species at a cavity facet. The TIR-ring design permits broadband cavity ring-down measurements of adsorbates, thin films, and liquids by eliminating the use of multilayer coatings. The basic sensing concept will first be reviewed by describing recent experiments employing a non-ring prototype in which a totally reflecting element was incorporated in a conventional ring-down cavity. The basic design issues for miniature TIR-ring cavities will then be briefly reviewed along with some numerical result obtained using a wave optics model that show the magnitude of different optical losses as a function of cavity size. A competition between losses results in an optimum size for chemical detection which occurs when the round-trip loss of the 'empty' cavity is minimized. The first experimental results will be presented for a square, fused-silica TIR- ring cavity for which the theoretically predicted photon decay time has been achieved.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Andrew C. R. Pipino "Evanescent wave cavity ring-down spectroscopy for ultrasensitive chemical detection", Proc. SPIE 3535, Advanced Sensors and Monitors for Process Industries and the Environment, (22 January 1999);

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