BEAM-SIZE EFFECT IN TIME-DELAYED LASER-INDUCED DOUBLE GRATINGS

We have studied theoretically the effect of the probe-beam size on tim e-delayed laser-induced double gratings by assuming that the probe bea m is described as a Gaussian beam. Letting E(s1) and E(s2) be the Four -Wave Mixing (FWM) signals originating from the diffraction of the pro be beam by the gratings, the condition for the occurrence of the FWM s ignal modulation is that the divergence angle of E(s1) and E(s2) is la rger than half of the intersection angle between the propagation direc tions of E(s1) and E(s2). We have also proposed methods to increase th e modulation contrast.