An optical narrowband switch between subluminal and superluminal light propagation in the inverted-Y configuration

摘要

The propagation of a weak probe field through a four-level inverted-Y type atomic system driven by two additional coherent fields, namely the control field and the repump field, is studied. The simulated probe absorption shows that electromagnetically induced transparency and the line shape of the transparency window under a Doppler-broadened condition are dependent on the residual Doppler averaging due to the wavelength mismatch between the control and probe fields. For Rb-87 the probe propagation changes from subluminal on-resonance under a Doppler-free condition to superluminal on-resonance under a Doppler-broadened condition. For both Rb-87 and Cs-133, the narrow subluminal window occurring in the group index profile in a Doppler-free environment offers an excellent delay bandwidth for probe field propagation. Under this condition, the order of the delay in probe field propagation can be as long as a few hundred mu s and seems quite promising in the field of optical delay generation and light storage. The analysis shows that the residual Doppler averaging has a greater impact on the switching window under the variation of the Rabi frequency of the control field as compared to that of the repump field.