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Raman Echo Data Storage in Pr:YSO Crystals for High Speed Imaging

M. S. Shahriar

Published May 1, 1998• 0 citations
OpenAlex

Abstract

We have demonstrated a ring cavity layer using the gain mechanism of a four-wave mixing process, mediated by two-photon Zeeman coherence resulting from coherent population trapping in a rubidium vapor cell. The cell acts as an amplifying phase conjugate mirror at one corner of the ring cavity. Even though the fundamental process requires non-degeneracy between the probe and the conjugate in the atom's frame, they are degenerate in the laboratory frame, via selection of a moving band of atoms for the gratings. As such, no frequency shifting is necessary in the cavity. The polarization orthogonality of the probe and the conjugate is compensated by an intra-cavity quarter wave plate.

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jan 8, 2015•0 citations
We have demonstrated a ring cavity layer using the gain mechanism of a four-wave mixing process, mediated by two-photon Zeeman coherence resulting from coherent population trapping in a rubidium vapor cell. The cell acts as an amplifying phase conjugate mirror at one corner of the ring cavity. Even though the fundamental process requires non-degeneracy between the probe and the conjugate in the atom's frame, they are degenerate in the laboratory frame, via selection of a moving band of atoms for the gratings. As such, no frequency shifting is necessary in the cavity. The polarization orthogonality of the probe and the conjugate is compensated by an intra-cavity quarter wave plate.
Summary form only given. Previously, we have used four-wave mixing via coherent population trapping to achieve optical phase conjugation (OPC) with high gain, using two dye lasers and a sodium vapor cell. The /spl Lambda/ transition used involved the two hyperfine ground states and one excited state, so that two different optical frequencies were needed to satisfy the two-photon resonant condition between the probe and one of the pump beams. Later, we demonstrated in rubidium that a single hyperfine transition with Zeeman sublevels is enough to achieve OPC with equally high gain, thus eliminating the need for high-frequency sideband generation. However, in order to guarantee that the diffraction from the grating is primarily dispersive, the backward pump beam had to be detuned by about 60 MHz from the probe and the forward pump. One of the key disadvantages of such a nondegenerate scheme is that applications such as phase-conjugate mirrors are hard to implement. Here, we report the observation of optical phase conjugation in rubidium with equally high gain, but all the frequencies are degenerate.
We report experimental observation of the enhancement and suppression of four-wave mixing and six-wave mixing (SWM) inside a ring cavity containing a rubidium atomic cell. greatly amplifies the SWM enhancement peak and suppression dip, and the vacuum induced Kerr nonlinear phase shift results in the asymmetric phenomenon of the SWM dressing effect. Additionally, we study the power switch and the destructive interference between multi-photon processes. Such investigation results can find applications in all-optical switches and optical communications.
We have observed the reflection of a probe laser beam by a three-dimensional optical lattice of rubidium atoms. The reflection spectrum shows different kinds of narrow resonances which we attribute to degenerate (phase conjugation) and non-degenerate multiwave mixing processes. In order to explain the extremely narrow linewidth (300 Hz) of the degenerate four-wave mixing resonance and its dependence on the angle of incidence of the probe, we propose a novel physical mechanism which includes the formation of a long-range atomic-density grating acting as a hologram.
In this study we show the results for parametric non-degenerate four wave mixing (FWM) obtained using double lambda scheme at D1 line in hot potassium vapor. We have investigated the influence of one-photon detuning and two-photon detuning on the FWM gain. The laser frequency is locked at approximately 1GHz from the resonance 4S1/2 Fg=1 -< 4P1/2, using external reference cavity. The probe beam passes through acoustooptic modulator that enables controllable detuning around 460 MHz (ground state hyperfine splitting) in respect to the pump beam. The vacuum glass cell containing the potassium vapor was heated by hot air in order to achieve necessary concentration of atoms. The efficiency of FWM process is studied by measuring the gains of the conjugate beam the probe beam, simultaneously. The maximal gain was achieved for nonzero two photon detuning.