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arXiv:1506.05240 · Physical Review A

Pulse splitting in light propagation through N -type atomic media due to an interplay of Kerr nonlinearity and group-velocity dispersion

Rajitha K. V., Tarak Nath Dey, Jörg Evers, Martin Kiffner

Published Aug 20, 2015• 10 citations
arXivHTMLPDF

Abstract

We investigate the spatiotemporal evolution of a Gaussian probe pulse propagating through a four-level $N$-type atomic medium. At two-photon resonance of probe and control fields, weaker probe pulses may propagate through the medium with low absorption and pulse shape distortion. In contrast, we find that increasing the probe pulse intensity leads to a splitting of the initially Gaussian pulse into a sequence of subpulses in the time domain. The number of subpulses arising throughout the propagation can be controlled via a suitable choice of the probe and control field parameters. Employing a simple theoretical model for the nonlinear pulse propagation, we conclude that the splitting occurs due to an interplay of Kerr nonlinearity and group-velocity dispersion.

DOI
10.1103/physreva.92.023840

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We investigate the spatiotemporal evolution of a Gaussian probe pulse propagating through a four-level NNN-type atomic medium. At two-photon resonance of probe and control fields, weaker probe pulses may propagate through the medium with low absorption and pulse shape distortion. In contrast, we find that increasing the probe pulse intensity leads to a splitting of the initially Gaussian pulse into a sequence of subpulses in the time domain. The number of subpulses arising throughout the propagation can be controlled via a suitable choice of the probe and control field parameters. Employing a simple theoretical model for the nonlinear pulse propagation, we conclude that the splitting occurs due to an interplay of Kerr nonlinearity and group-velocity dispersion.
A four-level N-type atomic medium is considered to study the effect of spontaneous generated coherence (SGC) and Kerr nonlinearity on light pulse propagation. A light pulse is propagating inside the medium where each atom follows four-level N-type atom-field configuration of rubidium ( 85 Rb) atom. The atom-field interaction leads to electromagnetically induced transparency (EIT) process. The atom-field interaction is accompanied by normal dispersion and in the presence of SGC and Kerr nonlinearity the dispersion property of the proposed atomic medium is modified, which leads to enhancement of positive group index of the medium. The enhancement of positive group index then leads to slow group velocity inside the medium. A more slow group velocity is also investigated by incorporated the collective effect of SGC and Kerr nonlinearity. The control of group velocity inside a four-level N-type atomic medium via collective effect of SGC and Kerr nonlinearity is the major part of this work.
We investigate nonlinear Kerr-induced coherence effect on a superluminal probing light pulse in a gain-assisted N-type 4-level atomic system via an intense monochromatic laser field. The dispersion exhibits a novel, interesting and useful two-paired double gain lines processes. The system displays lossless characteristics similar to [L. J. Wang, A. Kuzmich, A. Dogariu, Nature \textbf{406}, 277 (2000)] but with advantages of \emph{multiple} \textbf{controllable} anomalous regions, \emph{significantly enhanced} superluminal behavior and \textbf{relaxed} temperature, states of matter regardless of its isotropic or anisotropic conditions. Unlike the instability in [A. M. Akulshin, S. Barreiro, and A. Lezama, Phys. Rev. Lett. \textbf{82}, 4277 (1999)], the present system also \emph{overcomes the instable-limit} by the Kerr-induced coherence effect in the system. Indeed, the coherence enhances the group velocity remarkably by at least −30ms-30 ms−30ms more than of an instable Kerr-free system with almost negligible distortion in the retrieved pulse.
Under weak probe field, rotating wave and electric dipole approximations, we have derived analytic expressions for absorption and dispersion coefficients, group index and group velocity in a four-level cascade atomic medium interacting with the probe and pump laser fields. The model is applied to 85Rb atomic system to study the control of the fast and slow light propagation of the probe beam according to the intensity and frequency of the pump laser beam. With this excitation model, we find two transparent domains and thus the light group velocity is also controlled at these two frequency domains. In particular, the amplitude and the sign of the group index are easily changed by adjusting the intensity or frequency of the pump laser. That is, the probe beam propagation can be changed between fast and slow light modes by adjusting the intensity or frequency of the pump laser. Our analytical results can be useful for related experimental studies.
Abstract This paper describes the dynamics of solitonic pulse propagation in a closed loop quantum system comprised of five atomic energy levels. In this system four higher energy levels with four control laser fields form a closed ring-shape loop which is coherently coupled to a ground level state by a tunable probe laser field. Although the propagation of an intense probe pulse suffers losses and broadening in linear regime, there exist specific conditions where the probe pulse is found to become robust during its propagation. We attribute this regime to the formation of an optical soliton with a slow group velocity because of the balance between the dispersion and Kerr optical nonlinearity. Results obtained are based on the theoretical model using the coupled Maxwell–Bloch equations for the nonlinear propagation.