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arXiv:0711.4159 · Journal of Modern Optics

Control of superluminal transit through a heterogeneous medium

M. Kulkarni, N. Seshadri, V. S. C. Manga Rao, S. Dutta Gupta

Published Mar 1, 2004• 10 citations
arXivHTMLPDF

Abstract

We consider pulse propagation through a two component composite medium (metal inclusions in a dielectric host) with or without cavity mirrors. We show that a very thin slab of such a medium, under conditions of localized plasmon resonance, can lead to significant superluminality with detectable levels of the transmitted pulse. A cavity containing the heterogeneous medium is shown to lead to subluminal-to-superluminal transmission depending on the volume fraction of the metal inclusions. The predictions of the phase time calculations are verified by explicit calculations of the transmitted pulse shapes. We also demonstrate the independence of phase time on system width and the volume fraction under specific conditions.

DOI
10.1080/09500340408238067

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We consider pulse propagation through a two component composite medium (metal inclusions in a dielectric host) with or without cavity mirrors. We show that a very thin slab of such a medium, under conditions of localized plasmon resonance, can lead to significant superluminality with detectable levels of the transmitted pulse. A cavity containing the heterogeneous medium is shown to lead to subluminal-to-superluminal transmission depending on the volume fraction of the metal inclusions. The predictions of the phase time calculations are verified by explicit calculations of the transmitted pulse shapes. We also demonstrate the independence of phase time on system width and the volume fraction under specific conditions.
Pulse propagation through 1-dimensional stratified media is studied. The general features of pulse propagation in relation to the delay or advancement of the pulse are discussed. It is shown that in a lossless system with spatial symmetry the reflected and the transmitted pulses have the same delay or advancement. The phase times and the explicit output pulse profiles for an input Gaussian pulse are calculated. While recalling recent results for a variety of systems (resonant absorbers or heterogeneous medium in a Fabry-Perot cavity, a slab of negative index medium, a left-handed/right-handed periodic structure, etc.), new results involving coupled waveguides and a high finesse cavity containing an electromagnetically induced transparency (EIT) medium are presented. Calculations clearly show that for pulses with a carrier tuned at the resonance of the stratified media, one generally has subluminal propagation. Alternatively, in stop gaps or away from the resonances one ends up with superluminal transit. In the case of the EIT cavity it is shown that the large dispersion offered by the intracavity medium can lead to substantial superluminality (ng≃−106) with peak transmission as high as 20%. This is in sharp contrast to large signal attenuation for usual superluminal transit. Note also that EIT, to the best of the authors knowledge, has so far been used to achieve only slow light.
The reflection and transmission of a pulse through a slab which is doped with two-level or three-level atoms are investigated theoretically. The doped atoms can be passive (absorptive) or active (gain). We find that both the reflected and transmitted pulses can be superluminal simultaneously for the slab doped with absorptive two-level atoms at the slab thickness equal to (2m+1) lambda(0) /4 sqrt[epsilon(b)] (where lambda(0) is the center wavelength of the incident pulse, and epsilon(b) is the background dielectric constant of the slab) or with active three-level atoms at any thickness. By adjusting the thickness or background dielectric constant of the slab, the reflected pulse can be controlled from superluminal to subluminal or vice versa for the slab doped with absorptive two-level or absorptive three-level atoms. The energy percentage in the reflected pulse can also be controlled by changing the thickness of the slab, and the doped atoms.
Propagation of an electromagnetic pulse through a dielectric slab doped with three-level ladder-type atomic systems is discussed. It is shown that the group velocity of the reflected and transmitted pulses can be switched from subluminal to superluminal light propagation by the thickness of the slab or the intensity of the coupling field. Furthermore, it is found that, in the presence of quantum interference, the reflected and transmitted pulses are completely phase dependent. So, the group velocity of the reflected and transmitted pulses can only be switched from subluminal to superluminal by adjusting the relative phase of the applied fields.
Propagation of a light pulse through a dielectric slab is discussed theoretically in this paper. It is exhibited via a multiple-scattering approach that the slab can modify the phase of the pulse's frequency components, so that, when the frequency components are superposed, they cause the peak in the output pulse to appear to travel either faster or slower than in vacuum, depending on whether the slab is absorbing or amplifying. The expressions of the corresponding advancement and delay of the peak are derived and argued to be limited in magnitude by the pulse's duration.
A study about the reflection and transmission of an electromagnetic pulse through a slab doped with four-level atomic system has been presented. The doped atoms are considered to be in N-configuration with a pump field and a weak probe field. An additional control field is also applied to manipulate the Raman gain of the atomic medium. The propagation of transmitted and reflected pulses at different control field strengths and different slab thickness has been studied. It is found that the transmitted and reflected pulses can be simultaneously subluminal or superluminal. These pulses can be controlled from subluminal to superluminal by adjusting the strength of the control field
We show that the group velocity of a weak pulse can be manipulated by controlling the phases of two weak optical fields applied to a V-shaped three-level system. Such control can even cause the probe propagation to change from subluminal to superluminal. We consider two schemes: in the first, the excited states are coupled by decay-induced coherence, which is an inherent property of the medium, and in the second, quantum coherence is created by coupling the excited states to each other by a strong microwave field. We also discuss the group velocity reduction experienced by a single weak propagating probe due to decay-induced coherence.