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Frontiers in Optics

Normal and Anomalous Dispersion with Gain in Four Level System Coupled by Two Coherent Fields

Jyotish Kumar, Manoj Mishra, S. Shwetanshumala

Published Jan 1, 2024• 0 citations
Publisher

Abstract

The article explores the possibility of both subluminal and superluminal propagation in the same system. We find that the strength of the single coupling field and its detuning are like knobs to control propagation speed.
DOI
10.1364/fio.2024.jd4a.12

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We were able to arbitrarily control the speed of a light pulse from subluminal to superluminal velocity by changing only the power of the laser for coupling coherently the single transition between 62S1/2F=46{}^{2}{S}_{1/2}F=462S1/2​F=4 and $6{}^{2}{P}_{3/2}{F}^{\ensuremath{'}}=5$ in the D2{D}_{2}D2​ line of a Cs atomic vapor system. With weak coupling power, a Gaussian light pulse was propagated superluminally with a negative group velocity ${v}_{g}=\ensuremath{-}c/14400,$ which is caused by a highly anomalous dispersion related to an electromagnetically induced absorption. By increasing the coupling power at the same laser frequency, the pulses were propagated with a vacuum speed at the middle power and a subluminal group velocity vg=c/3000{v}_{g}=c/3000vg​=c/3000 at high power, which is caused by a normal dispersion related to an electromagnetically induced transparency. It was also found that group velocities depend largely on polarization combinations.