Interferometric characterization of the chromatic dispersion of gradient-index glasses

This research investigates the chromatic dispersion of gradient-index (GRIN) optical glasses. The wavelength dependence of the change in index of refraction ;A Mach-Zehnder configured interferometer with laser sources ranging from 442 nm to 633 nm measures the dispersion of thin plane-parallel GRIN samples. Optical phase measurements are made using harmonic phase-shifting interferometry for which the phase-shifting signal is the sum of two harmonics of prescribed amplitudes. A general analysis of harmonic phase-shifting interferometry is presented and applied to several pairs of harmonics. A tolerance analysis of the phase-shifting signal identifies configurations which are insensitive to variations in the relative phase of the two harmonics. The phase-shifting signal chosen is the sum of first-harmonic and second-harmonic sine waves with amplitudes equal to 0.328 and 0.488 waves respectively. With such a phase-shifting signal, the phase of the first harmonic in the detected photo-electric signal equals the optical phase of the interference pattern at the detector.;Additionally, the stress-induced birefringence in the GRIN samples is quantified by calculating the difference between index of refraction profiles measured with orthogonal, linearly polarized sources. A model that attributes the stress-induced birefringence to the gradient in the thermal expansion coefficient is presented and compared with measurements of the samples.