Adiabatic model of resonance two-photon self-focusing and defocusing of optical beams

A numerical and analytic investigation is made of the self-interaction of Gaussian beams under two-photon resonance conditions when the pulse duration is shorter than the relaxation times and the frequency detuning from resonance exceeds appreciably the spectral width of the radiation (adiabatic model). An analysis is made of defocusing (up-detuning) and self-focusing processes (down-detuning) in two-photon resonance. Three characteristic adiabatic self-focusing regimes are identified: a steady-state waveguide and weak and strong quasiwaveguide propagation. Expressions are derived for the critical powers and minimal self-focusing length.