Focusing of laser light outside a nonlinear crystal in second-harmonic generation with a pronounced energy exchange

The change in the phase of the light at the fundamental frequency in the course of second-harmonic generation is examined theoretically. This is a self-effect mechanism which operates in a medium with a quadratic nonlinearity. An analytic expression is derived for this phase as a function of the length of the crystal, the energy density of the light, the nonlinearity of the crystal, and the wave detuning. A numerical simulation shows that this mechanism should be taken into account along with other self-effect mechanisms in many cases of practical importance.