Convenient method for calibrating nonlinear phase modulators for use in phase-shifting interferometry

A method to calibrate a nonlinear phase modulator is described that is based on the minimization of a function obtained from a sequence of interferometric images. The method is equally applicable to smooth wavefront and speckled wavefront interferometry, allowing convenient in situ calibration for a wide range of interferometer configurations. The main advantage over previous calibration methods is that both the linear and quadratic phase variation terms are measured. The performance of the proposed method is verified by experiments in which the phase shift is determined independently by a Fourier transform method. (C) 1998 Society of Photo-Optical instrumentation Engineers.