G.J. Crofts

Continuous-wave Nd:YVO4 grazing-incidence laser with 22.5 W output power and 64% conversion efficiency

Abstract Very high-efficiency and high-power operation of a continuous-wave Nd:YVO 4 laser is demonstrated using a grazing-incidence geometry with diode side pumping. With 35 W diode bar pumping, multimode output power of 22.5 W (optical-to-optical conversion efficiency of 64%) with slope efficiency of 72%, and single mode output power of 13.8 W (conversion efficiency of 40%) is produced at wavelength 1064 nm. Small-signal gain and thermal lensing in the amplifier are investigated to explain the very high efficiency and spatial characteristics of the laser system.

Investigation of multipass geometries for efficient degenerate four-wave mixing in Nd:YAG

Degenerate four-wave mixing in the saturable gain of a flash-lamp-pumped Nd:YAG amplifier has been investigated. Three different geometries are examined in which the probe beam experiences (a) one pass, (b) two passes, and (c) four passes of the four-wave interaction region. It is found that multipassing the gain medium has a dramatic effect on the efficiency of the process, with a phase-conjugate reflectivity of 2500 and a conjugate energy extraction efficiency of greater than 200% demonstrated.

Phase conjugate reflectivity and diffraction efficiency of gain gratings in Nd:YAG

Abstract It is shown that gain gratings can be used as efficient phase conjugate and diffractive optical elements. Experimental results are presented of saturable gain four-wave mixing in a Nd:YAG amplifier using orthogonally polarised pump beams of pulse duration 16 ns. Phase conjugate reflectivity and diffraction efficiency are measured for both the reflection and transmission grating cases. Results show a higher efficiency for the transmission geometry. Transient (experimental results are comjpaed to a steady state theory.

Holographic laser resonators in Nd:YAG

We report the operation of Nd:YAG ring laser resonators formed by diffractive coupling from a gain volume hologram written in a Nd:YAG amplifier. Stable diffraction-limited output in a TEM(00) mode is demonstrated in a Nd:YAG system with thermal lensing and without the requirement of spatial mode control.

High-reflectivity four-wave mixing by gain saturation of nanosecond and microsecond radiation in Nd:YAG

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.

Self-starting Ti:sapphire holographic laser oscillator.

We demonstrate, for the first time to our knowledge, operation of a holographic laser oscillator that uses laser-pumped Ti:sapphire (Ti(3+) : Al(2)O(3)) as the gain medium. The device is self-starting and self-adaptive by virtue of spontaneous gain-grating formation. We present experimental results of the system that include gain-switched pulses of 25-60-ns duration in a TEM(00) mode and as much as 11 mJ of output energy from a plane output coupler and 47 mJ from an intracavity polarizer port.

Transient modeling of pulsed phase conjugation experiments in a saturable Nd:YAG amplifier

Abstract We model the transient dynamics of degenerate four-wave mixing in a saturable gain medium. We confirm that the transmission gain grating case has a higher reflectivity than the reflection grating case in correspondence to experiments. A transient model of self-pumped phase conjugation in a saturable amplifier in a loop arrangement is compared to a pulsed experiment in a Nd:YAG amplifier. Results from the model show agreement in the behavioural characteristics of the experimental system. Dynamical evolution of the system is described with reference to temporal build-up of the gain gratings during the writing pulse and the subsequent erasure during the lasing output pulse.

Spatial characteristics of a laser oscillator formed by optically-written holographic gain-grating

Abstract We investigate the spatial characteristics of a Nd:YAG unidirectional ring resonator formed by an adaptive holographic gain-grating. Diffraction-limited spatial output is demonstrated from the resonator even with very strong intracavity phase distortion. We also show that, despite good intracavity phase compensation and good spatial output quality, the output mode size is not generally the same as the self-intersecting input beam that forms the gain hologram. A simplified theory, to account approximately for a spatially-Gaussian input beam, gives qualitative agreement with the key features observed in the experimental resonator.

High-phase-conjugate reflectivity (<800%) obtained by degenerate four-wave mixing in a continuous-wave diode-side-pumped Nd:YVO(4) amplifier.

High-phase-conjugate reflectivities of >800% have been achieved through degenerate four-wave mixing in a cw diode-side-pumped Nd:YVO(4) amplifier. Reflectivity curves are shown as a function of input pump-beam intensity for three values of small-signal amplifier gain, and comparison is made with a numerical simulation.

Tunable phase conjugation in a Ti:sapphire amplifier

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.