A Criterion for Using Spectral Interferometry in Far Infrared Dispersion Measurements

High precision index measurements (n/n 10^-5) have been recently achieved on an AgGaS₂ crystal using a spectral interferometry technique with a polarized white-light continuum. Up to now, these measurements are limited to the visible and near-infrared range, the most dispersive domain. We investigate the possibility to extend the technique to far infrared index measurements. We demonstrate a criterion depending only on group velocity dispersion and crystal thickness for planning future experiments.