The paramagnetic optical Faraday rotation is the averaged property of all the energy states of the paramagnetic ion. Therefore, any perturbation of the population distribution of the energy states caused by the microwave power absorption would manifest itself as the interaction between the optical Faraday rotation and the microwave radiation. A general calculation of this effect, plus some experimental results, are presented in this paper. An attempt is made to analyze the behavior and to evaluate the applications as optical modulators, detectors, and relaxation measuring devices.
William S. C. Chang and James Q. Burgess, "Optical Faraday Rotation and Microwave Interactions in Paramagnetic Salts," Appl. Opt. 1, 329-333 (1962)