Induced-modulation-instabilities limit to "fast" light propagation

Summary form only given. A recent technique for creating "fast" light pulses (i.e. pulses of light having group velocity greater than c or less than zero) uses a continuous-wave bichromatic Raman pump laser beam to tailor the dispersion properties of an atomic vapor. We have discovered a number of effects that impose limits on fast-light propagation as the gain increases. Most important is the modulation instability, a nonlinear effect that can lead to temporal modulation of intense continuous-wave laser fields. We discuss the induced modulation instability in the context of high-gain bichromatically driven atomic systems, specifically in the context of fast-light pulse propagation. We further discuss the practical limitations that the induced modulation instability imposes on this method for creating faster-than-c pulses.