Effect of Resonant Collisions on the Propagation of a Self-Induced Transparency Pulse in SF6

Effect of the SF6 pressure on self-induced transparency (SIT) in SF6 was investigated systematically. The study consists of measuring the shape, width, delay time, and intensity of the transmitted pulse (which is a SIT pulse at low SF6 pressure) as a function of SF6 pressure P. The SIT pulse was induced by the nonlinear interaction of a 20-nsec P(20) CO2 laser pulse with the SF6. A theory which includes the homogeneous broadening mechanism was developed for the pulse delay time. For a stationary propagating pulse, it was found that the pulse delay time is related nonlinearly to Q (the ratio of the transiently energy stored energy density to the rate of change of the energy flux density of the field). From the interpretation of the experimental results, it was concluded that, for P>100 μ, the SF6-SF6 resonant collision makes a significant contribution to the departure from SIT. The effect of level degeneracies associated with the high angular momentum of the involved resonant vibrational states is also discussed.