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.
D. D. Archibald, C. E. Miller, L. T. Lin, and D. E. Honigs, "Remote Near-IR Reflectance Measurements with the Use of a Pair of Optical Fibers and a Fourier Transform Spectrometer," Appl. Spectrosc. 42, 1549-1558 (1988)