INVARIANT PULSE-PROPAGATION AND SELF-PHASE MODULATION IN DENSE MEDIA

Analytical solutions for the slowly varying phase as well as the field amplitude are obtained for invariant pulse propagation in resonant absorbing media consisting of interacting two-level atoms. Such media, having many atoms within a cubic wavelength, have been shown to exhibit large frequency chirps in pulse propagation owing to near-dipole-dipole interactions. Departures from hyperbolic-secant pulse envelopes and pulse areas other than 2-pi have been shown to occur in invariant pulse propagation. We show that self-phase modulation results from the near-dipole-dipole interactions and can cause strong modification of pulse shapes, including temporal narrowing and multipulse behavior.