Measurement of Magneto-Optic and Thermo-Optic Properties of Optical Medium.

Experimental work on the measurement of thermo -optic and nonlinear magneto-optic properties of optical media is presented. In studying magneto-optic effects, balanced homodyne interferometry has been used. This interferometric scheme utilizes two orthogonal principal components of a polarization state as separate arms of a conventional two beam interferometer. A series of experiments proves that balanced homodyne interferometry is the best method for measuring the small change in a polarization state of an optical field. Quantum noise limited sensitivity has been achieved with relatively low noise laser sources: 1 mW single frequency and 3 mW multi-mode He-Ne lasers. Measured values of the Cotton-Mouton coefficients of Faraday materials (Tb^{+3}, Ce^ {+3}, and Pr^{+3} rare earth composite materials, and diamagnetic materials such as ZnSe) and some liquid solvents (benzene, chloroform, acetone, and water) are presented. Significantly large Cotton-Mouton coefficients, which have a strong dependence on the paramagnetic susceptibility and concentration of rare earth ions presented in the materials, were observed for the paramagnetic Faraday materials. Difficulties introduced into the measurement of a small Cotton-Mouton effect caused by misalignment and/or an inherent linear birefringence of a crystalline sample are discussed. In studying thermo -optic properties of silicon, time resolved infrared radiometry has been used. The time evolution of gray-body emission was studied after pulsed heating by a laser. By the use of a one-dimensional thermal diffusion equation, a theoretical description for the transient thermal radiation can be developed. Results obtained for relatively heavily doped samples (~.002 Omega cm) show that pulsed photothermal radiometry is an excellent remote diagnostic technique for silicon over a wide range of relatively heavy doping levels. For lightly doped samples (~5 Omega cm), an anomalously large thermal radiation signal is observed that contradicts the predictions of the thermal diffusion model. This phenomenon can be explained by the enhancement of the gray-body emissivity due to laser generated free carriers. A simple theoretical model for this free carrier effect is presented.