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Optics Letters

Tunable phase conjugation in a Ti:sapphire amplifier

Graham J. Crofts, X. Banti, Michael J. Damzen

Published Aug 1, 1995• 24 citations
Publisher

Abstract

Four-wave mixing by gain saturation in a laser-pumped Ti:sapphire (Ti(3+):Al(2)O(3)) amplif ier is demonstrated for the f irst time to our knowledge. Small-signal gain in excess of 250 has been obtained by intense laser pumping at 532 nm, resulting in observed four-wave mixing energy ref lectivity as high as 360% for nanosecond pulses at 780 nm.

DOI
10.1364/ol.20.001634

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Four-wave mixing by gain saturation in a laser-pumped Ti:sapphire (Ti(3+):Al(2)O(3)) amplif ier is demonstrated for the f irst time to our knowledge. Small-signal gain in excess of 250 has been obtained by intense laser pumping at 532 nm, resulting in observed four-wave mixing energy ref lectivity as high as 360% for nanosecond pulses at 780 nm.
The theory of phase conjugation in laser amplifiers by saturable-gain degenerate four-wave mixing with copolarized beams is developed for pulses of arbitrary temporal shape and duration in the limit of a weak signal beam. The influence of the input pulse’s characteristics (energy, temporal pulse shape, duration) on the phase-conjugate reflectivity and on the conjugate pulse shape is analyzed. A sharp instantaneous peak of phase-conjugate reflectivity is predicted at high intensities of the four-wave mixing beams. This effect is experimentally demonstrated at λ0 = 1064 nm in a Nd:YVO4 amplifier pumped by a cw Ti:sapphire laser. A transient peak reflectivity of R ∼ 50% is thus obtained, corresponding to an enhancement of 1.6× compared with the maximum steady-state reflectivity. The experimental results and the theoretical predictions are in good agreement.
High-reflectivity four-wave mixing by gain saturation in a Nd:YAG laser amplifier is demonstrated. With a four-pass geometry, the phase-conjugate reflectivity of a Q-switched pulse (18-ns duration) is ∼2500, and for a long pulse (relaxation oscillation duration ∼100 μs) it is ∼30. Temporal and energy characteristics of the conjugate beam are presented. A phase-conjugate Nd:YAG TEM00 laser resonator is also produced in which the Nd:YAG rod is simultaneously the laser gain medium and the phase-conjugating device.
Phase conjugation in a Cr(4+):YAG saturable absorber by degenerate four-wave mixing with nanosecond pulses at lambda = 1.06 mu m is demonstrated for the first time to our knowledge. An experimental phase-conjugate energy ref lectivity of ~2% and an overall eff iciency of ~0.4% are achieved. Because of the presence of absorbing dipoles oriented along specif ic directions, it is shown that the phase-conjugated beam can be made orthogonally polarized relative to the signal beam or to both pump beams with almost no reduction of the energy reflectivity.