Self-induced transparency (SIT) has been observed under the conditions of sharp-line absorption, i.e., with an inhomogeneous absorption width only one-fourth the spectral width of the pulse. A 5-nsec pulse from a
202Hg ii laser intersected perpendicularly an atomic beam of natural rubidium. The beam slits reduced the Doppler absorption width to about 30 MHz. A particular resolved
MI transition of
85Rb was scanned into coincidence with the laser pulse by a 75-KOe magnetic field. With peak absorption depths of 3-6, nonlinear transmission, pulse delays, pulse breakup, and peak amplification were seen and found to be in excellent agreement with sharp-line computer solutions of the Maxwell-Bloch equations. The experimental realization of the sharp-line SIT is of interest because analytical formulas for pulse evolutions are more plentiful and because sharp-line SIT might permit compression of picosecond pulses.
The present paper has the dual purposes. As the first purpose, it is demonstrated that the boson description of Wannier excitons introduced in the preceding paper is suitable also to discussion of non-linear coherent interaction of Wannier excitons with the radiation field. The second purpose is to discuss the possibility of self-induced transparency due to Wannier excitons on the basis of the boson description by making clear the difference between a two-level atomic system and a system of excitons which can propagate in a crystal as polariton. As a result, stable pulse propagation of the radiation field is shown to be prevented by the polariton effect of excitons.