Remote Near-IR Reflectance Measurements with the Use of a Pair of Optical Fibers and a Fourier Transform Spectrometer

Abstract

A commercial near-infrared (near-IR) Fourier transform (FT) spectrometer was modified to make remote reflectance measurements over a single optical fiber or pair of optical fibers. With the use of two low-hydroxyl fused-silica optical fibers and an InSb detector, the near-IR region from 0.92 to 2.15 μm was measurable. An InGaAs detector was used to obtain reflectance spectra over the region from 0.92 to 1.56 μm. With this detector, single-fiber reflectance and transmission measurements were possible and a variety of dual-fiber probe geometries could be easily employed. Dual-fiber geometries were used to enhance pathlength, to perform depth discrimination, and to make measurements without physical contact between the probe and the specimen. Potential applications and improvements are discussed.