Multichannel transmission ellipsometer for characterization of anisotropic optical materials

We have developed a multichannel transmission ellipsometer to characterize the wavelength dependence of the optical characteristics of transparent, anisotropic solids. The source side of the instrument employs a broadband lamp in conjunction with a rotating polarizer. The light transmitted through the sample is analyzed by a stationary polarizer, a grating spectrograph, and a 1024-pixel photodiode array. The photodiode array collects irradiance spectra at several uniformly spaced values of the rotating polarizer angle P, and the irradiance registered at each pixel of the array is Fourier analyzed versus P. From this analysis one can characterize the change in polarization state induced by the sample as a continuous function of wavelength from 400 to 800 nm. The multichannel transmission ellipsometer can be applied in studies of linear and circular birefringence in new materials as well as in assessments of the spectroscopic performance of polarization modifying devices such as retarders. However, we also emphasize the application of the instrument as an educational tool for demonstrating polarization concepts in advanced undergraduate physics and optics laboratories. In this application anisotropies in common optical materials have been characterized, including circular birefringence in quartz and linear birefringence and dichroism in mica. Because high-precision data are collected continuously versus wavelength, the results represent a clear improvement over those obtained at discrete wavelengths.