Large nonlinear phase shift owing to cascaded χ^(2) in quasi-phase-matched bulk LiNbO_3

Large nonresonant effective nonlinear indices that are due to cascading have been observed by Z-scan and CCD camera measurements performed on quasi-phase-matched LiNbO₃. Positive and negative values of $n_2^{\mathrm{cascad}}$ were measured at temperatures symmetrically displayed with respect to the optimum phase-matching temperatures ($2.39\times {10}^{-13}$ and $-2.37\times {10}^{-13} {\mathrm{cm}}^2/\mathrm{W}$, respectively).