Changes in the structure of a focal region due to spatial self-focusing of short pulses

A theoretical analysis is given of the trebling in the number of focal points as a result of self-focusing of short pulses. It is shown that such trebling occurs when certain conditions are obeyed by the relationship between the pulse duration and the initial beam divergence (linear focus). Motion of a nonlinear focus is analyzed and intensity distributions are obtained for media with instantaneous or delayed nonlinear response.