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arXiv:1111.3826

Linear and Nonlinear Pulse Propagations in Lifetime-Broadened Atomic Media with Spontaneously Generated Coherence

Chao Hang, Guoxiang Huang

Published Nov 16, 2011• 0 citations
arXivHTMLPDF

Abstract

The linear and nonlinear pulse propagations in lifetime-broadened three-state media with spontaneously generated coherence (SGC) are investigated theoretically. Three generic systems of V-, $Λ$-, and $Ξ$-type level configurations are considered and compared. It is shown that in linear propagation regime the SGC in the V-type system can result in a significant change of dispersion and absorption and may be used to completely eliminate the absorption and largely reduce the group velocity of a probe field. However, the SGC has no effect on the dispersion and absorption of the $Λ$- and $Ξ$-type systems. In nonlinear propagation regime, the SGC displays different influences on Kerr nonlinearity for different systems. Specifically, it can enhance the Kerr nonlinearity of the V-type system whereas weaken the Kerr nonlinearity of the $Λ$-type system. Using the SGC, stable optical solitons with ultraslow propagating velocity and very low pump power can be produced in the V-type system by exploiting only one laser field in the system.

DOI
10.48550/arxiv.1111.3826

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The linear and nonlinear pulse propagations in lifetime-broadened three-state media with spontaneously generated coherence (SGC) are investigated theoretically. Three generic systems of V-, ΛΛΛ-, and ΞΞΞ-type level configurations are considered and compared. It is shown that in linear propagation regime the SGC in the V-type system can result in a significant change of dispersion and absorption and may be used to completely eliminate the absorption and largely reduce the group velocity of a probe field. However, the SGC has no effect on the dispersion and absorption of the ΛΛΛ- and ΞΞΞ-type systems. In nonlinear propagation regime, the SGC displays different influences on Kerr nonlinearity for different systems. Specifically, it can enhance the Kerr nonlinearity of the V-type system whereas weaken the Kerr nonlinearity of the ΛΛΛ-type system. Using the SGC, stable optical solitons with ultraslow propagating velocity and very low pump power can be produced in the V-type system by exploiting only one laser field in the system.
We propose a new scheme to generate stable ultraslow optical solitons in lifetime-broadened three-state V-type media via spontaneously generated coherence (SGC). We show that in the linear propagation regime, SGC in the system can result in a significant change of dispersion and absorption, which may be used to completely eliminate absorption and greatly reduce the group velocity of the probe field. In the nonlinear propagation regime, SGC can largely enhance the Kerr nonlinearity of the system. By means of SGC, stable optical solitons with ultraslow propagating velocity and ultralow generation power can be produced. Different from previous works, ultraslow optical solitons obtained in the present system based on SGC have much smaller attenuation during propagation and can be created by using only one laser field.
We study phase control of linear and nonlinear optical responses in a three-level atomic system in V-configuration exhibiting spontaneously generated coherence (SGC). Because of the SGC effect, the strength of Kerr nonlinearity strongly depends upon the relative phase between the probe and control fields as well as the absorptions. By controlling the relative phase appropriately, large Kerr nonlinearity can be achieved with canceled linear and nonlinear absorptions. Combining with the phase modulation, the strict decay condition of spontaneous decay rates is not needed.
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.
The effects of spontaneously generated coherence (SGC) on the propagation of a weak probe pulse are investigated in a ladder-type atomic system. Due to SGC, the properties of the dispersion and the absorption of a three-level ladder-type system are changed greatly. With proper parameters, the system can produce normal and anomalous dispersion regions in the gain region. The effects of the incoherent pumping and the relative phase on the group velocity are also studied. They all can be used as switches to manipulate the group velocity of the weak probe field from gain-assisted sub- to superluminance.
We investigate the reverse saturable absorption (RSA) and optical limiting (OL) in a three-level V-type quantum system considering the effect of the spontaneously generated coherence (SGC). It is shown that in the absence of the SGC effect, the saturable absorption (SA) is dominant in the system. By taking into account the SGC effect, we prove that the SA dramatically switches to the RSA. Moreover, it is demonstrated that the OL threshold and OL efficiency can be controlled by the SGC effect. In addition, we show that the applied field properties such as detuning can modify the SGC-induced optical limiter efficiency. It is also shown an increase in the atomic density and length of the medium makes the optical limiter more efficient. The analytical calculation shows that the Kerr nonlinearity caused by the SGC effect is the main mechanism of the system evolution. Finally, the theoretical Z-scan experiment is presented to confirm the obtained results. Our proposed scheme can be useful to design controllable atomic optical limiters for optical devices with different sensitivities.
In this article, a theoretical scheme is proposed to investigate the formation and propagation of three-wave coupled vector optical solitons with ultraslow group velocities in a lifetime-broadened seven-state triple-$\ensuremath{\Lambda}$ atomic system under Raman excitation. We show that in the presence of a weak applied magnetic field that removes the degeneracy of the corresponding sublevels of the atomic medium, three continuous-wave control fields with circularly left or right polarized fields induce a quantum interference effect which can largely suppress the absorption of the three low-intensity pulsed fields, that is, the circularly ${\ensuremath{\sigma}}^{\ensuremath{-}}$ (right), the linearly $\ensuremath{\pi}$, and the circularly ${\ensuremath{\sigma}}^{+}$ (left) polarized fields converted from one weak linear-polarized probe field. By means of the standard method of multiple scales, we solve the equations of motion of atomic response and probe-control electromagnetic fields and derive three-coupled nonlinear Schr\"odinger equations that govern the nonlinear evolution of the envelopes of the probe fields in this scheme. We then demonstrate that because of the nonlinear coupling to one another, the three probe fields can evolve into three-wave temporal, group velocity, and amplitude-matched optical solitons under appropriate conditions, which are produced from the delicate balance of the dispersion effects and the self- and cross-phase modulation effects. This scheme may thus pave the way to generate ultraslow vector optical solitons composed of three field components in a highly resonant atomic medium and result in a substantial impact on this field of nonlinear optics.