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Nonlinear optics of a few-cycle optical pulse: slow-envelope approximation revisited

Using Maxwell-Bloch equations, we analyze the response of an ensemble of two-level atoms driven by a femtosecond optical pulse beyond the traditional approach of slowly varying amplitudes and phases. For optical pulses of a given duration, we show that the off-resonance optical field can evolve into a stable (spatio-) temporal soliton.