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AIP conference proceedings

Excitation Energy and Temperature Dependence of the Phase Coherent Photorefractive Effect

A. Kabir, H. P. Wagner, Jisoon Ihm, Hyeonsik Cheong

Published Jan 1, 2011• 0 citations
Publisher

Abstract

We investigate the influence of excitation energy and temperature on the phase coherent photorefractive (PCP) effect in ZnSe quantum wells. At temperatures below 35 K and nearly exciton resonant excitation the formation of trions suppresses the PCP effect. At lower excitation energies increasing space‐charge‐fields reduce the trion binding energy which leads to an enhanced thermal ionization of trions resulting in a PCP signal. Due to the thermal dissociation of trions at temperatures exceeding 40 K a strong PCP effect occurs even at nearly resonant excitation.

DOI
10.1063/1.3666453

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We investigate the influence of excitation energy and temperature on the phase coherent photorefractive (PCP) effect in ZnSe quantum wells. At temperatures below 35 K and nearly exciton resonant excitation the formation of trions suppresses the PCP effect. At lower excitation energies increasing space‐charge‐fields reduce the trion binding energy which leads to an enhanced thermal ionization of trions resulting in a PCP signal. Due to the thermal dissociation of trions at temperatures exceeding 40 K a strong PCP effect occurs even at nearly resonant excitation.
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We investigate the spectral and thermal dependence of an exciton resonant all-optical and phase coherent photorefractive effect in a ZnSe single quantum well by four-wave mixing using 90fs90\phantom{\rule{0.3em}{0ex}}\mathrm{fs}90fs pulses. The observed phase coherence is attributed to an exciton-induced formation of an electron grating within the quantum well. The diffracted signal exhibits an exponential decay that is equal to the exciton dephasing rate and it shows a pronounced suppression at the temporal overlap of incident pulses. With decreasing photon energy the diffracted signal traces reveal faster decay and the exciton transition is shifted towards lower energies indicating an increasing electron concentration within the quantum well. In temperature dependent measurements we observe a filling of the signal dip at pulse overlap and a transition from the photorefractive effect to a ${\ensuremath{\chi}}^{(3)}$ four-wave-mixing process below 35K35\phantom{\rule{0.3em}{0ex}}\mathrm{K}35K. Additional experiments using a cw pump laser are consistent with the proposed mechanism of the observed photorefractive effect. The phase coherent photorefractive signal is reproduced by a phenomenological model that is based on the optical Bloch equations for a five-level system.
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