Quantitative analysis of Raman signal enhancement from aqueous samples in liquid core optical fibers

Raman scattering from aqueous liquids can be collected with high efficiency by enclosing the liquid within a suitable waveguide, as several groups have reported. Here, we present a quantitative model that predicts the relative strength of signals collected from (a) a tubular waveguide and (b) a flat-walled cuvette. Experimental measurements of Raman scattering from aqueous ethanol are made using two geometries, a Teflon-AF waveguide and a standard quartz cuvette. The model correctly predicts the enhancements in several ethanol Raman bands provided by the waveguide geometry. This model should be useful in aligning and characterizing liquid core waveguides, whose manufacture is still undergoing refinements. In particular, the model shows that absorption and scattering losses affect the enhancement factor in different ways.