Abstract: A system for nonlinear frequency conversion includes an acousto-optic modulator for diffracting a portion of an input laser beam as a first-order beam and transmitting a non-diffracted portion of the input laser beam as a zeroth-order beam. The system also includes a nonlinear crystal arranged to receive and frequency convert each of the zeroth-order and first-order beams to generate two respective frequency-converted laser beams, whereby, when the acousto-optic modulator changes the average-power ratio between the zeroth-order and first-order beams, variations of the heat load in the nonlinear crystal are minimized. Either one of the two frequency-converted laser beams may be used as an output laser beam of the system, while the other one of the two frequency-converted laser beams serves to stabilize the heat load in the nonlinear crystal when the acousto-optic modulator is operated to change the average power in the output laser beam.