Suppression of self-focusing for few-cycle pulses

Intense beams of light propagating through a medium with a positive Kerr nonlinearity can undergo self-focusing provided that their average power is larger than a certain critical power determined by the wavelength and material properties of the medium. Here, we show that for pulses comprising only a few optical cycles, this self-focusing can be inhibited by the presence of significant (normal) dispersion. We derive simple expressions to quantify the threshold power for self-focusing in the presence of dispersion. In addition, we show that under certain conditions, this threshold power can be larger than conventional critical power (for a dispersionless case) by a factor as large as several hundred.