Dressed state analysis of electromagnetically induced transparency in a five-level X-type atomic system with wavelength mismatching effects

We present the theoretical study of the wavelength dependence of electromagnetically induced transparency (EIT) in a five-level X-type atomic system using dressed state approach. Our numerical calculations reveal that the EIT response of the composite X-type system is more intricate than its constituent Lambda and two Xi subsystems. We derive an analytical solution for probe coherence using the perturbation technique. In the case of stationary atoms, EIT control is possible by varying the strengths and/or the detunings of strong electromagnetic fields. The dressed state picture is employed to describe the position and strength of each peak in probe absorption profile. We also explore in- depth the effect of Doppler broadening on EIT for perfect (lambda(p) = lambda(c1) < lambda(c2) = lambda(c3)) and various partial wavelength mismatching schemes (lambda(p) = lambda(c1) > lambda(c2) > lambda(c3) and lambda(p) = lambda(c1) < lambda(c2), lambda(c3)). Our results manifest that when lambda(p) = lambda(c1) > lambda(c2), lambda(c3), mixing of one Doppler free Lambda and two Doppler broadened Xi subsystems results in splitting of absorption and dispersion profiles. Further we substantiate that transparency in a Doppler-broadened medium depends not only on the two-photon EIT positions, but also on the positions of the Autler-Townes components across the various velocity groups. The group index and group delay time profiles become broad on increasing the wavelength mismatching factors.