A theoretical study of the group refractive index n _g in a four-level inverted Y-type system formed by ⁸⁷Rb atom – laser radiation interaction

Abstract

We report a theoretical investigation of the dispersion resulting from electromagnetically induced transparency (EIT) and the associated group refractive index profiles n g of a four-level inverted Y-type system formed by the interaction of three optical fields (probe, pump and control) with 87Rb atoms. The density matrix equations are derived from the semi-classical Liouville’s equation and solved both numerically and analytically to study the coherent nonlinear optical properties of the medium. We first present the EIT, dispersion and corresponding group index profiles n g under the switch-on/off and on/off-resonance conditions of the pump and control lasers. In presence of both pump and control lasers, an enhancement of the EIT window, a sharp EIT spike and related steeper dispersion slopes are obtained at the line centre of the probe frequency detuning. The group index profiles with the variation of the strengths of individual applied optical fields are studied. The effect of the ground state decoherence rates on the group index profile is examined in detail. It is found that the manipulation of n g values and the corresponding group velocities ν g of the probe light can be easily controlled from subluminal to superluminal values or vice versa by changing the strengths of the applied fields and the ground state decoherence rates. Besides, the EIT-based ‘optical switching’ phenomenon in the medium is explained by studying the variation of the group index with the pump and control Rabi frequencies.

Theoretical study of coherent optical phenomena in a three lasers driven four-level ladder-type system involving a Rydberg state

“…Particularly, we are interested to study both the two-and three-photon induced coherent optical phenomena, such as EIT, EIA, TPEIT, TPEIA and their related dispersion spectra, group index, FWM, etc by the detection of probe field. To study these various coherent phenomena in the three lasers driven four-level laddertype system involving a Rydberg state, we set up the density matrix equations which are derived from the semi-classical Liouville's equation of motion [17,19,47],…”

“…The EIT and EIA are two-photon induced coherence phenomena where the absorption of the atomic medium remarkably reduces and enhances, respectively. The last few decades have witnessed quite extensive studies of two-photon induced EIT and EIA both theoretically and experimentally due to their potential applications in atomic clocks [15], storage of light pulses [16], spontaneously generated coherence [17], slow and fast light effects [18], optical switching [19], etc. The EIT and EIA phenomena have been extensively studied in the three-or four-or five-or higher-level atom-laser coupling systems which are either generic lambda (Λ), vee (V), ladder (Ξ)-type or some complex combinations of these generic systems [6][7][8][9][10][11][12][13][14][20][21][22][23][24][25].…”