Comparative study of some fiber-optic remote Raman probe designs .1. Model for liquids and transparent solids

We have developed models describing the sensitivity and sampling volume of various remote fiber-optic Raman probes-single-fiber, lensed, dual-fiber beveled-tip, dual-fiber Rat-tipped, and multi-fiber Rat-tipped. The models assume clear samples and incorporate radii, separation, bevel angle, and numerical aperture of the fibers; overlap geometry of illumination and excitation light cones; and refractive index of immersion medium. For the Raman spectra of solid samples in air, single-fiber and lensed probes are predicted to yield the highest Raman signal. Beveled probes should provide greater Raman signal strength than do flat-tipped probes because beveled probes can collect light from a restricted volume closer to the probe end, Although multiple collection fibers improve Raman signal strength, progressively distant concentric fiber rings contribute less and sample material further from the probe.