This paper presents a temporal investigation of the propagation of a single laser beam in a photorefractive medium, both in the continuous and pulsed regimes. A time resolved observation of one beam self-focusing in electrically biased Bi 12 TiO 20 (BTO) is reported for the two time scales. To interpret these experimental results, two (1+1) dimensional theoretical models of the propagation of one laser beam in a photorefractive crystal have been developed, numerically simulated using a BPM calculation and successfully compared to our experimental observations.