Authors: Cooney, Thomas F.¹; Skinner, H. Trey²; Angel, S.M.²

Source: Applied Spectroscopy, Volume 50, Issue 7, Pages 12A-32A and 823-955 (July 1996) , pp. 849-860(12)

Publisher: Society for Applied Spectroscopy

Abstract:

We compare relative performances of flat-tipped, beveled (two-fiber and six-around-one), and single-lensed focused fiber-optic Raman probes and, where feasible, evaluate the utility of optical filters for reducing fiber background. The sensitivity profile of each probe is determined by measuring the relative intensity of light backscattered off a flat surface as a function of distance from the probe tip. The experimental results are compared with a simple light-cone-overlap model incorporating fiber numerical aperture, fiber and immersion medium refractive indices, separation between excitation and collection fibers, number of fibers, and fiber bevel angle and/or lens focal length. The model and sensitivity profiles are used to interpret the sampling regions for Raman spectra obtained by using each of the probes with a clear, transparent sample (single-crystal sparry calcite), a white, partially transparent sample (acetaminophen tablet), and a set of organic liquids of varying refractive index. The sensitivity of the tested commercial lensed probe drops off symmetrically about the focal point. For both solid samples, the intensity of fiber background follows a profile determined primarily by laser backscattering off the surface, whereas the sample Raman signal follows a profile dependent upon sampling depth.

Keywords: Raman spectroscopy; Remote sensing; Fiber-optic sensors

Document Type: Research article

DOI: http://dx.doi.org/10.1366/0003702963905574

Affiliations: 1: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208; Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822 2: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208

Publication date: 1996-07-01

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