Effect of diffraction on the nonlinear propagation of optical few-cycle pulses

The effect of diffraction on the propagation of optical few-cycle pulses in an isotropic nonlinear dielectric is studied. A great difference is found between the nonlinear diffraction of such pulses and nonlinear diffraction of quasi-monochromatic pulses with a distinct carrier frequency. It is shown that, when the number of pulse oscillations is smaller than a certain critical value, diffraction cannot prevent pulse self-focusing at any power of the pulse.