Experimental studies of gyrotropy of crystals

A phenomenon that is not yet fully understood theoretically and has been studied only slightly, and which has a number of distinctive properties as being the strongest manifestation of spatial dispersion. The conclusions of the phenomenological macroscopic theory and their agreement with experiment are discussed briefly. The best-suited substances are summarized, and the nature of the propagation of light waves in crystals is described. A microscopic treatment of the problem is presented with a number of examples of the beststudied crystals. The extent of agreement between theory and experiment, the relation of the gyrotropy to the crystal structure and of its constituent elements to the energy levels (electronic, vibronic, and vibrational) and to exciton effects are analyzed. Molecular, ionic, and covalent crystals and semiconductors are discussed; magnetoelectric media and liquid crystals are covered. Studies published up to the beginning of 1974 are used.