Nonlinear phase shift without cascaded second-order processes and third-order nonlinearity

A new mechanism for obtaining a nonlinear phase shift has been proposed and schemes are described for its implementation. As it is shown, the interference of two waves with intensity-dependent amplitude ratio coming from the second-harmonic generation should produce the nonlinear phase shift. The sign and amount of nonlinear distortion of a beam wavefront is dependent on the relative phase of the waves that is introduced by the phase element. The calculated value of n₂ ^eff exceeds that connected with cascaded quadratic nonlinearity, at the same conditions. Received: 1 November 1999 / Published online: 23 February 2000