Some aspects of propagation phenomena in an optically thick medium of two-level atoms with a complementary leak transition from the upper state

Abstract We study the effect of an additional leak transition from the upper state of a resonantly excited transition, on the propagation phenomenon known as coherent small scale self focusing, arising in optically thick atomic vapours. We show how to modelize the behaviour of the laser beam by introducing an initial aperture effect followed by Fresnel diffraction, leading to an annular intensity distribution pattern.