Evanescent-wave spectroscopy down infrared transmitting optical fibers

Richard D. Driver; James N. Downing; Garett M. Leskowitz

doi:10.1117/12.56580

1 January 1992 Evanescent-wave spectroscopy down infrared transmitting optical fibers

Richard D. Driver, James N. Downing, Garett M. Leskowitz

Proceedings Volume 1591, Infrared Fiber Optics III; (1992) https://doi.org/10.1117/12.56580
Event: OE Fiber, 1991, Boston, MA, United States

Abstract

The evanescent-wave spectrum of a sample surrounding the core of an optical fiber is a complex function of the optical constants of the media involved as well as the geometry of the sensing fiber. We develop a simple theory for evanescent-wave absorption in the weak absorption limit where we show that the absorbance of a length of sensor fiber may be related linearly to the bulk sample absorption coefficient. We present experimental data that verifies the observed scaling between the evanescent-wave absorbance and the bulk absorption coefficient for an isopropanol sample. The application of evanescent-wave spectroscopy with different sensor fiber materials is discussed, along with experimental and theoretical data for the enhancement of evanescent-wave spectroscopy using tapered fibers. Finally we discuss the results of a numerical series of calculations based on the exact ray paths of radiation within the fiber and the fundamental theory of ATR absorption at an interface assuming a plane wave approximation. In the more complex theory the evanescent-wave absorption coefficient is a decreasing function of the bulk absorption coefficient.

Citation Download Citation

Richard D. Driver, James N. Downing, and Garett M. Leskowitz "Evanescent-wave spectroscopy down infrared transmitting optical fibers", Proc. SPIE 1591, Infrared Fiber Optics III, (1 January 1992); https://doi.org/10.1117/12.56580

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