Generation of a pure phase-modulated pulse by the cascading effect: a theoretical approach

New techniques to produce spatiotemporal phase modulation without the use o f electro-optic devices are proposed and discussed. By using the nonlinear second-order effect in crystal it is possible to change the amplitude modul ation of a pump wave into the phase of a signal wave. To that end, we propo se the use of a well-known cascading configuration for which the phase mism atch is high. Analytical results of spatial and temporal incoherent phase m odulation are developed with the correlation function formalisms. Furthermo re, highly accurate expansions of signal phase and intensity are derived. T he effects of group-velocity difference, group-velocity dispersion, and dif fraction on the change of amplitude into phase modulation are studied. Fina lly, an experimental demonstration of a KDP crystal with a sinusoidal pump modulation that creates sinusoidal phase modulation is proposed. (C) 2000 O ptical Society of America.