We present a multiple-input, single-output, weakly nonlinear model of
spatial light modulators by use of a second-order Volterra series and
describe an experimental method to measure the nonlinear transfer func
tions by means of sinusoidal perturbation and synchronous detection wi
th a lock-in amplifier. We also present an application of this method
to a liquid-crystal light valve. (C) 1998 Optical Society of America.