Waveguide Sampling for Analytical Raman Spectroscopy

The requirement that the sample have a refractive index higher than the sample tube material is essential to completely constrain the light inside the sample. This is a stiff constraint, and it rules out the use of aqueous samples n 1.33) in silica (n = 1.55) unless the requirement for total internal reflection is relaxed (see below). Some modem variations of Walrafen s approach broaden the technique to aqueous samples by reducing the refractive index of the sample tube below that of water. Specially formulated fluoronated copolymers with n = 1.29 — 1.31 can be extruded as capillaries to contain the sample (30,31). Total internal reflection is maintained for most aqueous solutions, since they have a refractive index greater than the tube material. 

Configuration Laser Wavelength Sample Enhancement Reference 

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