LARGE PHASE-SHIFTS DUE TO THE CHI((2)) CASCADING NONLINEARITY IN LARGE WALK-OFF AND LOSS REGIMES IN SEMICONDUCTORS AND OTHER DISPERSIVE MATERIALS

The nonlinear phase shift associated with chi((2)) cascading was studi ed for ultrashort pulses in regimes with large temporal walk-offs betw een tile fundamental and the chi((2))-generated second-harmonic (SH) p ulses, a situation typical of semiconductors. Despite the small overla p between the fundamental and SH pulses after they walk-off each other : a nonlinear phase shift was numerically observed to occur at a rate comparable to that before they walk-off. A pi/2 phase shift was demons trated even in a waveguide 15 times longer than the walk-off length.