Continuous control of light group velocity from subluminal to superluminal propagationwith a standing-wave coupling field in a Rb vapor cell

摘要

We present the continuous control of the light group velocity from subluminal to superluminal propagation with an on-resonant standing-wave coupling field in the 5S_(1/2)-5P_(1/2) transition of the A-type system of ~(87)Rb atoms. When a coupling field was changed from a traveling-wave to a standing-wave field by adjusting the power of a counterpropagating coupling field, the probe pulse propagation continuously transformed from subluminal propagation, due to electromagnetically induced transparency with the traveling-wave coupling field, to superluminal propagation, due to narrow enhanced absorption with the standing-wave coupling field. The group velocity of the probe pulse was measured to be approximately 0.004c to —0.002c as a function of the disparity between the powers of the copropagating and the counterpropagating coupling fields.