Resonance self-focusing of coherent light pulses in absorbing media

It is shown that analytical and numerical solutions of the Maxwell-Bloch equations containing time-dependent and transverse phase shifts predict the existence of on-resonance self-focusing as a result of the combined effect of diffraction and time-lag of the medium's response. It is shown that this type of self-focusing can be characterized by simple parameters expressed in terms of the parameters of the medium and the laser beam. Experiments in which this self-focusing effect was clearly demonstrated are noted.