
Mode-Locking Based on Nonresonant Nonlinearity 349
6.4. MODE-LOCKING BASED ON NONRESONANT
NONLINEARITY
Various techniques of mode-locking using second-order nonlinearities have
been developed. A first method is a direct extension of Kerr lens mode-locking,
which has been analyzed in the previous chapter. A giant third-order susceptibility
can be found near phase matching conditions in SHG, not unlike the situation
encountered with a third-order susceptibility, which is seen to be enhanced near
a two photon resonance [36,37]. In this method, called cascaded second-order
nonlinearity mode-locking, the nonlinear crystal is used in mismatched conditions