Role of multiphoton ionization in the short-wavelength broadening of the spectrum of a light bullet in the middle infrared range

The short-wavelength cutoff of the anti-Stokes wing of the supercontinuum in the spectrum of a light bullet at filamentation of femtosecond radiation at a wavelength tunable in a wide range of the middle infrared range in fused silica and fluorides has been studied for the first time. A physical model for the formation of the spectrum of the light bullet has been proposed on the basis of the spectral broadening caused by the phase selfmodulation of the light field on the trailing edge of the light bullet at the generation of a plasma in the process of multiphoton ionization. Within this model, a function has been obtained to determine the wavelength shift of the short-wavelength cutoff as a function of the multiphoton order. This function is in agreement with experimental results.