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IEEE Journal of Quantum Electronics

Dynamics of transient probe beam amplification via coherent multiwave mixing in a local nonlinear medium-nematic liquid crystal

Iam Choon Khoo, Ping Zhou, Liang Yu, Hong Li

Published Jan 1, 1993• 8 citations
Publisher

Abstract

The dynamics of the transient thermal-grating-mediated probe-beam amplification effect in a nematic liquid crystal film is studied with the use of millisecond laser pulses. These experimental observations and the accompanying transient multiwave mixing analysis show that peak probe gain can occur at various locations within the grating decay time; the higher the induced index change, the sooner will peak gain occur.>

DOI
10.1109/3.259414

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Physical Review A•May 1, 1990•3 citations
The dynamics of the transient thermal-grating-mediated probe-beam amplification effect in a nematic liquid crystal film is studied with the use of millisecond laser pulses. These experimental observations and the accompanying transient multiwave mixing analysis show that peak probe gain can occur at various locations within the grating decay time; the higher the induced index change, the sooner will peak gain occur.>
In a highly nonlinear thin film, the presence of the diffracted beams from the pump-probe-beam-induced refractive-index grating modifies considerably the energy coupling between the pump and the probe beams. Using coupled amplitude and phase equations, the roles of various factors such as phases and phase shifts, phase modulations, pump-beam intensity, intensity ratio, interaction length, and losses in the medium in the multiwave-mixing processes are clearly identified. We also present experimental results on the dependence of the probe gain on the pump-probe-beam ratio, the pump intensity, and on the interaction length, using a nematic liquid-crystal film as the nonlinear medium.
We present a detailed quantitative theory of transient multiwave mixing effects in a nonlinear medium produced by two incident coherent laser beams. Our theory accounts for all the relevant parameters such as laser pulse widths, medium response times, nonlinearities, interaction length, intensities, beam ratio, phase-modulation effects, losses, side diffractions, and explicitly shows how the dynamics and the multiwave mixing processes are interrelated with these parameters. The crucial role played by the diffracted beams and the time-dependent phase shifts among the beams and the interplay among the various intensity and index gratings are explicitly evaluated. In particular, the gain experienced by a weak incident probe beam via these mixing effects from the incident strong pump beam is investigated as a function of the aforementioned parameters.
We present a detailed general theory of multiwave mixing effects in a nonlinear medium produced by two incident coherent laser beams. Calculations are performed for localized as well as diffusive types of nonlinearities. The theory accounts for all the relevant parameters such as laser pulse widths, medium response times, nonlinearities, interaction length, intensities, beam ratio, phase modulation effects, losses, and side diffractions. The interrelationship between two- and multiwave mixing effects and the evolution of transient to stationary behavior is explicitly worked out. In particular, the gain experienced by a weak incident probe beam via these mixing effects is quantitatively analyzed as a function of the aforementioned parameters.