This research is aimed at the development of a high speed, optical polarization modulator for use in polarimeters and ellipsometers. The objective will be to reach modulation frequencies of 10-20 kHz and in a manner which is independent of light frequency. The rotational modulator will be used in the construction of a high speed polarimeter and ellipsometer for the purpose of making rapid and accurate determinations of transient structural changes in solids, liquids, and thin films. These instrumentations will have important advantages compared with previous designs with respect to the speed of data acquisition and improved capabilities, such as the ability to make spectroscopic measurements of properties like birefringence and dichroism.