Self-focusing of a single laser pulse in a photorefractive medium

An original experimental and theoretical time-resolved study of a single laser pulse self-focusing in a nonlinear photorefractive medium is reported. The behavior of the self-focusing process is experimentally observed in a photorefractive ${\mathrm{Bi}}_{12}{\mathrm{TiO}}_{20}$ crystal during the 5 ns pulse duration of a doubled Nd:YAG (yttrium aluminum garnet) laser. A theoretical interpretation is provided, based on a simple model of photorefraction on the nanosecond time scale.