New method for determining the nonlinear optical coefficients of thin films

A new scheme for characterizing the quadratic optical nonlinearity of thin films grown on opaque substrates is proposed and demonstrated. This involved the measurement, as a function of the film thickness, of second-harmonic waves reflected from a film surface. The d36 coefficient of a ZnSe-on-GaAs film is estimated by this method to be 33±7 pm/V at the fundamental wavelength of 1.06 μm, which agrees reasonably well with the known value for the bulk crystal.