Stability and Group Index Switching in a Four-Level Atomic System

Dingan Han, Yaguang Zeng, Yanfeng Bai +4 more

Hossein Jafarzadeh, Ahmadi Sangachin Elnaz, Seyyed Hossein Asadpour

A four-level atomic system is proposed for stability and group index switching in the presence of spontaneously generated coherence. It is found that the transition from optical bistability (OB) to optical multistability (OM) and subluminal to superluminal can be obtained simultaneously. It is shown that the relative phase between applied fields can affect the stability and group index behaviors of weak probe light in the medium. Our proposed model provides a new scheme for simultaneous switching from OB to OM and (sub-to-super) luminal light propagation in an atomic system.

Nguyen Van Phu, Nguyen Huy Bang, Luong Thi Yen Nga +1 more

Abstract The optical response of a magnetic-degenerated four-level atom system to the two left and right circular polarization components of the probe field is represented at room temperature. The absorption spectrum and group index for the two polarization components of the probe field are controlled according to the static magnetic field and the coupling field under electromagnetically induced transparency condition. By varying the strength of the static magnetic field, the optical response of the atomic medium can be changed from transparency to absorption or vice versa and hence the amplitude of group index also changes from positive extreme to negative extreme or vice versa. The same phenomenon also occurs when changing the coupling field intensity. In addition, temperature also significantly influence on the optical response of the atomic medium, which changes not only the amplitude but also the sign of the group index as the temperature increases. Our analytical results can be useful for experimental observation and related applications of light group index/velocity at room temperature.

A.S. Shumovsky, R. Tanaś, Tran Quang

Shang-qi Kuang, Ren-Gang Wan, Jun Kou +2 more

We theoretically investigate the influence of a coherent pump field on the propagation of a weak light pulse of a probe field in a four-level atomic system. Due to the modulation of the pump field, the light pulse can be manipulated from subluminal to superluminal with negligible distortion. This scheme can be realized in both the ultracold and Doppler-broadened atomic systems. We also demonstrate that the spectral linewidth with an anomalous dispersion is reduced by thermal averaging; therefore, one can obtain a larger negative group refractive index in room-temperature vapor than the largest value achieved in ultracold atomic gas.

P. J. Manson