Refractive index dispersion functions of solid-phase polymers by multicolor optical diffraction

Ford, J. V.; Sumpter, B. G.; Noid, D. W.; Barnes, M. D.; Otaigbe, J. U.

Chemical and Analytical Sciences Division

Oak Ridge National Laboratory

Oak Ridge, TN, USA

Abstract

We show that fourth-order dispersion functions of solid-phase polymers can be detd. by multicolor optical diffraction. Electrodynamically trapped microparticles of polyethylene glycol with different mol. wts. were probed by two-dimensional optical diffraction with four different laser wavelengths (632.8, 514.5, 488.0, and 457.9 nm); subsequent Mie anal. of one-dimensional scattering patterns yielded size and refractive index (both real and imaginary parts). Using a single wavelength as a size ref., the nonlinear dependence of the refractive index of solid (nonevaporating) polymer microparticles was detd. by finding the refractive index for a given wavelength that best matched a Mie calcn. subject to the ref. size constraint. The exptl. detd. refractive index values were fit to a std. fourth-order Cauchy function to obtain values for n0, n1, and n2.