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Journal of Modern Optics

Effect of Ion-ion Coulomb Scattering in Plasma on the Photon Echo Decay

L.A. Gel'Medova, David A. Shapiro

Published Jan 1, 1992• 1 citation
Publisher

Abstract

The extra photon echo decay due to ion-ion, velocity-changing collisions is computed. The strong velocity dependence of the collision frequency is shown to decrease the decay constant by 30%.
DOI
10.1080/713823353

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We investigate a mechanism responsible for the observed very short times of the photon-echo decay (of the order of a few femtoseconds) in semiconductors. It is associated with the loss of phase memory as a result of the interaction of the interband mixed state with an unscreened random Coulomb potential of the photocarriers and/or charged impurities. A time characteristic of a system of interacting electrons is found. This is the time of phase breaking ${\mathrm{\ensuremath{\tau}}}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$, which we calculate within the eikonal approximation using diagrammatic techniques. ${\mathrm{\ensuremath{\tau}}}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$ is shown to be typically much shorter than both the time of electron-electron collisions and the period of plasma oscillations. We demonstrate that the screening of Coulomb potential cannot be built up during this time. ${\mathrm{\ensuremath{\tau}}}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$ is proportional to ${\mathit{n}}^{\mathrm{\ensuremath{-}}1/\mathit{d}}$ (where n is the carrier concentration and d the dimensionality of a system), which is consistent with the experimental results. The derived law of echo decay of the form exp[-(\ensuremath{\tau}/${\mathrm{\ensuremath{\tau}}}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$)d{)}^{\mathit{d}})d] agrees with the results of numerical simulation, although it does not agree with the existing results of physical experiment. We believe that such a disagreement is of a fundamental nature and manifests a basic need for further experimental and theoretical work.
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