  The new mechanism for obtaining a nonlinear phase shift has been proposed and
the 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 of the
relative phase of the waves that is introduced by the phase element. Calculated
value of $n_2^{eff}$ exceeds that connected with cascaded quadratic
nonlinearity, at the same conditions.
