In a form analogous to the methods for the measurement of optical constants, a set of methods for the measurement of their changes is described. The methods compared measure light reflected at different angles, with different experimental arrangements; the conclusions reached are demonstrated experimentally with Ge, by electroreflectance measurements.
E. SCHMIDT and W. H. KNAUSENBERGER, "Determination of the Change of Optical Constants by Modulation Techniques," J. Opt. Soc. Am. 59, 857-861 (1969)