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

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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.