Small beam non-paraxiality arrests self-focusing of optical beams

A new equation for self-focusing in the presence of small beam nonparaxiality is derived. Analysis of this equation shows that nonparaxiality remains small as the beam propagates. Nevertheless, nonparaxiality arrests self-focusing when the beam width becomes comparable to its wavelength. A series of focusing-defocusing cycles of decreasing magnitude follows, ending with a final defocusing stage.