We describe a method which enables us to determine the linear and quadratic electro-optic coefficients (real and imaginary parts) of thin stratified films even inside the absorption range. The principle is based on the interferences between the electric-field-induced modulation of the transverse electric and transverse magnetic reflected waves. Experiments performed on a poled polymer yield microscopic parameters such as the excited and fundamental state permanent moments and the difference and transition moments which are in a very good agreement with other determinations. The presence of an excited state not detected by linear spectroscopy was revealed.