Quantitative Raman Spectroscopy of Homogeneous Molecular Profiles in Optical Waveguides Using Internal Standards

Abstract

Quantitative agreement between measured Raman signals and calculated integrated electric field intensity distributions is demonstrated in both three- and four-layer waveguides by the use of one member of the thin-film structure as an internal standard with which to eliminate the influence of all mode-varying parameters. Optical parameters were obtained in four-layer structures from a negative gradient search along the four-dimensional error surface and were then used to generate integrated electric field distributions. Experiments on poly(styrene)/poly(vinyipyrrolidone)/SiO₂ structures showed excellent (r² = 0.9999) linearity between measured and calculated values for cutoff modes, but a spectral interference prevented use of the modes which were active in both layers. Substitution of poly(styrene-d₈) enabled a comparison of calculated and measured Raman signal ratios to be made for all modes, and again excellent linearity (r² = 0.9985) was obtained.