This paper present new experimental and theoretical result concerning the temporal dynamic of the self focusing process, proving that it is characterized by two time scales: one on the order of microseconds, the other on the order of milliseconds. A four quadrants position detector was used to characterize the beamu27s temporal evolution after propagating into an InP:Fe crystal 1cm in length, subjected to an applied field of 10 kV/cm. "Asymmetry", which is proportional to the offset to the beam with respect to the centre of the detector, equal to 0 corresponds to a perfectly circular beam centered on the detector, while a non-null asymmetry indicates a deviation and/or a deformation of the beam. Theoretical analysis allows calculating the diameter and the deviation of the self focused beam at each moment during the propagation. In conclusion, it is proved that the faster time scale is influenced by the intensity, while the second is mostly influenced by the temperature.
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