The optical deflection efficiency of an acousto‐optic modulator with a lead molybdate interaction medium has been measured at optical wavelengths in the region 442–1152 nm. The crystal orientation was such that the acoustic beam propagated along the optic axis and the optical beam near theaaxis. The dependence of the relative figure of merit on optical wavelength and polarization has thus been determined. The results indicate that the figure of meritM2is independent of the optical polarization at 633 and 1152 nm, but that a considerable and unexpected sensitivity to polarization occurs between 442 and 515 nm.