HIGH-ORDER NONLINEAR PHASE-SHIFT CAUSED BY CASCADED 3RD-ORDER PROCESSES

We show, for the first time to our knowledge, that the fundamental bea m that participates in the process of third-harmonic generation experi ences an additional high-order nonlinear phase shift. The magnitude of the shift is proportional to the square of the pump intensity and the length of the sample and depends on the deviation fi om the exact pha se-matched condition. This phase shift arises from cascaded third-orde r processes. Its value can exceed the value of the phase shift. that o riginates from inherent fifth-order susceptibility of the nonlinear me dium. its sign is controllable by the sign of the phase mismatch of th e third-harmonic generation process. (C) 1997 Optical Society of Ameri ca