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 i nterferometric images. The method is equally applicable to smooth wave front and speckled wavefront interferometry, allowing convenient in si tu calibration for a wide range of interferometer configurations. The main advantage over previous calibration methods is that both the line ar and quadratic phase variation terms are measured. The performance o f the proposed method is verified by experiments in which the phase sh ift is determined independently by a Fourier transform method. (C) 199 8 Society of Photo-Optical instrumentation Engineers.