K. S. Syed

Self-adaptive solid-state laser oscillator formed by dynamic gain-grating holograms

We describe the operation of a self-starting Nd:YAG laser oscillator incorporating a design in which laser oscillation occurs by means of diffraction from spontaneously generated three-dimensional gain gratings produced by spatial hole burning in the Nd:YAG amplifier. The transient onset and spectral selectivity of the gain gratings produce an output with energy of 600 mJ in a 10-ns single-longitudinal-mode pulse at 10 Hz. The self-adaptation of the gain gratings produces compensation of intracavity phase distortion. A transient numerical modeling of the nonlinear resonator gives good agreement with the experimental system and also provides insight into the temporal dynamics of the gain grating.

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.

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.

Transverse effects in ultrabroadband multifrequency Raman generation

The theory of ultrabroadband multifrequency Raman generation is extended, for the first time, to allow for beam-propagation effects in one and two transverse dimensions. We show that a complex transverse structure develops even when diffraction is neglected. In the general case, we examine how the ultrabroadband multifrequency Raman generation process is affected by the intensity, phase quality, and width of the input beams, and by the length of the Raman medium. The evolution of power spectra, intensity profiles, and global characteristics of the multifrequency beams are investigated and explained. In the two-dimensional transverse case, bandwidths comparable to the optical carrier frequency, spanning the whole visible spectrum and beyond, are still achievable.

Transient modelling of a self-starting holographic laser oscillator

We simulate the transient behaviour of a self-starting holographic laser oscillator using a numerical model which can account, to arbitrary strength, for one, two and four gain gratings within the saturable amplifying medium. The dependence of output energy on parameters such as intracavity gain and output coupler reflectivity is investigated, thereby enabling the optimisation of extraction efficiency and the understanding of oscillation and grating dynamics.

Transient modelling of double-pumped phase conjugation in inverted Nd:YAG

Abstract Transient modelling of double-pumped phase conjugation (DPPC) in gain media is presented. Numerical results for reflectivity, diffraction efficiency and temporal behaviour of an injected DPPC system and self-starting DPPC laser are discussed. An experimental gain DPPC system and self-starting version are then modelled, and a comparison is made between numerical and experimental results.

Transient modeling of a self-starting holographic laser oscillator

3. In (l) , the output fluence decreases when the depolarization induced by the h/4 into the loop increases, whereas in (2) the output fluence remains almost constant. The configuration (2) not only compensates for the phase aberrations but also for the depolarization aberrations. Indeed, in (2), both [loo] and [ O l O ] types of absorbing dipoles are sampled, which can lead to equal conjugate reflectivities along those two orthogonal axes forming a base, and thus to vectorial phase conjugation (VPC)? In (I) , only the [ loo] type of dipoles is sampled, as a consequence, VPC is not performed. In conclusion, Cr4+:YAG used in its specific configuration which can correct polarization aberrations appears as a promising nonlinear medium to realize SPPCM in NdYAG loop resonators. Such resonators produce selfQswitching by dynamic absorption grating formation, achieve greater-than-unity reflectivities, and can compensate for both intracavity phase and polarization aberrations.

Self-pumped phase conjugation in a solid-state gain medium

nificant (G 20).‘ Attempting to obtain higher gain by increasing the pump intensity or the amplifier length will result in increased amplification of the noise in the signal channel, even in the absence of an input signal, and a decrease in gain. In this work a model Brillouin amplification which includes noise and pump depletion3 is further developed, in order to understand the theoretical limitations to efficiency. This effort leads to the following equation which relates the pump depletion ratio 5 = Po,,JP, to the input power ratio q = Ps JP,, the ratio of pump to noise2 power R = PJ4rokT and G: