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.

Abstract: MOPA apparatus includes a mode-locked fiber laser delivering seed-pulses to a regenerative amplifier. The seed-pulses are transported via one of two lengths of optical fiber. One of the lengths of fiber is significantly longer than the other, and significantly increases the duration of the seed-pulses. Amplified seed-pulses are compressed in a pulse-compressor. The pulse compressor delivers pulses having a pulse-duration of either a few picoseconds, or less than one picosecond, depending on whether the seed pulses are transported respectively by the longer or shorter of the lengths of optical fiber.