Manipulating light through Zeeman EIT in ⁸⁷Rb vapor: impact of temperature and beam parameters

We study Zeeman Electromagnetically Induced Transparency (EIT) in an effective three-level closed \(\Lambda\) $\mathrm{\Lambda }$ system involving the \(D_{2}\) $D_2$ transition of \(^{87}{Rb}\) $_{}^{87}\mathit{Rb}$ . The impact of coupling intensity and detuning, cell temperature, beam diameters, and transit relaxation rate are explored in a controlled manner on EIT width and peak transmission. Narrow EIT features of FWHM \(\approx 36\) $\approx 36$ kHz and peak transmission \(\approx 92\%\) $\approx 92\%$ are noted. The dispersive characteristics of the \({^{87}{Rb}}\) $_{}^{87}\mathit{Rb}$ atomic medium, affecting the group index and group delay of the probe beam are also examined. The group index of the atomic medium has a nonlinear dependence on the coupling intensity, indicating that an optimization of the latter is required to attain a maximum reduction of the group velocity for slow light. For a probe beam diameter of 1.5 cm, a maximum group delay of 0.228 \(\upmu\) $\mathrm{\mu }$ s can be achieved corresponding to a group velocity of \(v_{g}\) $v_g$ = \(\frac{c}{914}\) $\frac{c}{914}$ m/s. Our study especially highlights the impact of a detuned coupling beam on the probe transmission and its group delay. An interesting aspect of a negative group delay is noted for a sufficiently detuned coupling beam at low intensity which signifies the conversion from slow light to fast light.