Pulse delay of a stimulated Raman process in atomic vapor

We experimentally demonstrate two types of peak-peak delay effects in linear and high-gain saturation regions of a stimulated Raman process in Rb87 atomic vapor. The delay time linearly increases with the intensity of the Raman pump field in the linear Raman amplifier due to the slow-light effect but is independent of the intensity of the input weak seed pulse. In contrast, in a high-gain saturation region, the delay time decreases with the intensities of not only the Raman pump but also the input seed fields because of the large Raman coupling coefficient and serious depletion of the atoms. In particular, when the input seed contains several photons per pulse on average, the peak-peak delay time linearly decreases with the number of photons in the input seed pulse, showing that the Stokes seed at the few-photon level still has a significant effect on the peak-peak delay.