Wavelength mismatching effects on susceptibility and optical switching in an inverted-Y type atomic system

Abstract

We investigate the effect of the residual Doppler averaging on the susceptibility and optical switching of a weak probe field propagating through a four-level inverted-Y type atomic system driven by two strong coherent fields, namely the pump field (control field) and the repump field. A theoretical model of the inverted-Y type system is developed by using density matrix method and a set of sixteen optical Bloch equations (OBEs) are solved analytically under steady state condition to determine the probe coherence term. The imaginary part of susceptibility shows electromagnetically induced transparency (EIT) under Doppler free condition as well as under Doppler broadening. The line parameters of 5S1/2 → 5P3/2 → 5D5/2 and 5S1/2 → 5P3/2 → 7S1/2 transitions executed by 87Rb atoms are used to simulate the susceptibility and group index related to probe field propagation in order to show the effect of residual Doppler broadening due to wavelength mismatch between the pump field and the probe field. Under Doppler free condition the probe field propagation is subluminal on resonance while that under Doppler broadened condition is superluminal on resonance for both the transitions.