M.J. Damzen

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.

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.

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.

Bragg-selectivity of a volume gain grating

Abstract We adapt the theory of volume grating holography to model analytically the diffraction efficiency of a volume gain grating and its variation due to deviation from Bragg-matching. We present modelling of the case when the gain grating is optically-written in a saturable laser amplifier by spatial hole burning, under both steady-state and transient conditions. We perform an experimental measurement of the angular-sensitivity of a volume transmission gain grating optically-written in a Nd:YAG amplifier rod. It is shown that the amplification of the writing beams needs to be considered since this leads to a spatial variation of the grating modulation depth and thereby to the reduction of its angular sensitivity compared to the uniform grating case.

Phase conjugate self-organized coherent beam combination: a passive technique for laser power scaling

In this Letter, a first (to our knowledge) demonstration of phase conjugate self-organized coherent beam combination is reported. A demonstration involving combination of two self-adaptive gain grating holographic laser resonators is presented. Output powers of up to 27 W, with a combination efficiency of 94%, are demonstrated. This technique coherently combines individual phase conjugate laser modules, which do not have predefined spectral or spatial modes. This removes the problem of finding shared resonator modes, which should allow coherent beam combination of much larger laser arrays than standard self-organized coherent beam combination.

Intensity-induced birefringence in Cr4+: YAG

Abstract We studied both experimentally and theoretically the transmission and polarization characteristics of a Cr4+ : YAG saturable absorber crystal as a function of the intensity and polarization state of an incident laser beam. We found that a birefringent absorption behaviour is induced and we show that the experimental results are well described by a full numerical model which includes excited-state absorption as well as a ground-state cross-absorption term. By using pump-probe measurements we show that a finite cross-saturation of the absorption is achieved along the crystal axes orthogonal to the polarization of the optical radiation. No induced refractive index birefringence is observed.

Vectorial phase conjugation via four-wave mixing in isotropic saturable-gain media

We study theoretically the properties of transient degenerate four-wave mixing in an isotropic, homogeneously saturable gain medium with interacting beams of arbitrary strength and polarization state. In particular we investigate the ability of the interaction to exhibit vectorial phase conjugation when orthogonally circularly polarized pump beams are used. This mechanism allows the correction of both phase and polarization distortions introduced to an optical beam. Numerical simulations are compared with experiments that use a flashlamp-pumped Nd3+:YAG amplifier and demonstrate good vector phase-conjugate fidelity for both weak and strong probe beams of arbitrary polarization state.

Transient analysis of four-grating copolarized four-wave mixing in saturable gain media with finite probe

We model transient copolarized degenerate four-wave mixing in a saturable gain medium, using pulses of duration much shorter than the population lifetime with a finite probe beam. Initially we describe a model to include the simultaneous existence of both the reflection and transmission gratings for arbitrary field strengths. Then we develop a model to include all four possible gratings, including standing-wave gratings between counterpropagating pump beams and the probe and conjugate beams. By use of two expansion methods for the higher-order grating terms it is possible to model regimes in which either one grating is arbitrarily strong or all four gratings are strong. Comparisons are made among models including one, two, and four gratings. Good agreement is found between the theoretical four-grating case and pulsed copolarized degenerate four-wave mixing experiments in laser-pumped Ti:sapphire for a finite probe beam.

Experimental investigation of vector phase conjugation in Nd 3+ :YAG

We present a study of vector phase conjugation based on degenerate four-wave mixing in inverted Nd:YAG. The results demonstrate polarization correction for weak probe strength, with near-unity fidelity for polarization compensation of the returning conjugate. As the probe strength is increased, the fidelity of the polarization state of the conjugate is seen to deteriorate to an average value of 92% when the probe is strongly saturating and is several times stronger than the pump beams. We also show that, for strong probe strengths, an individual transmission grating or reflection grating is more efficient than when both gratings are present.

Numerical modelling of continuous-wave holographic laser oscillators

The continuous-wave operation of a self-adaptive laser which oscillates by diffraction from a gain hologram is modelled numerically. We demonstrate the greater-than-unity diffraction efficiency of a single gain grating and show how the properties of an externally-written gain grating laser lead to the realization of an entirely self-starting system. The dependence of output power on parameters such as intracavity gain and output coupler reflectivity is investigated, thereby enabling the optimisation of power extraction and improving understanding of steady-state holographic laser action.