Controllable ultrabroadband slow light in a warm rubidium vapor

We study ultrabroadband slow light in a warm rubidium vapor cell. By working between the D1 and D2 transitions, we find a several-nanometer window centered at 788:4 nm in which the group index is highly uniform and the absorption is small (<1%). We demonstrate that we can control the group delay by varying the temperature of the cell, and we observe a tunable fractional delay of 18 for pulses as short as 250 fs (6:9 nm bandwidth) with a fractional broadening of only 0.65 and a power leakage of 55%. We find that a simple theoretical model is in excellent agreement with the experimental results. Using this model, we discuss the impact of the pulse’s spectral characteristics on the distortion it incurs during propagation through the vapor. © 2011 Optical Society of America OCIS codes: 060.1155, 190.0190, 020.0020.