
105Self-Focusing and Nonlinear Effects
Chapter 4
band and corresponding range of nal levels of the conduction band. Since dierent
combinations of simultaneously absorbed laser photons provide dierent values of inter-
band transition probability, all channels of the photoionization transitions should be
nonlinearly coupled and compete with each other. is qualitative consideration leads to
important conclusions: (1) the photoionization rate by signicantly nonmonochromatic
pulses should be much higher than the rate for the monochromatic approximation, and
(2) the photoionization must result in specic modications of laser spectrum. So far, ...