NUMERICAL INVESTIGATION OF THE SELF-FOCUSING OF BROAD-BANDWIDTH LASER-LIGHT WITH APPLIED ANGULAR-DISPERSION

The self-focusing of phase-modulated broad-bandwidth (BBW) laser light , in which the spectral components are angularly dispersed to produce smoothing of laser nonuniformities, is analyzed. A multifrequency, mul tidimensional computer code has been developed to simulate the propaga tion of angularly dispersed BBW light within a nonlinear medium. Earli er work has shown that the self-focusing behavior of phase-modulated B BW light without angular dispersion is insignificantly different from that of monochromatic beams. With the addition of angular dispersion, pure phase modulation cannot be maintained during propagation, and the beam becomes subject to the development of spatial amplitude modulati on which moves across the beam in time. Instantaneously, this amplitud e modulation will begin to self-focus in a nonlinear medium. However, when examined over one period of the phase modulation, the time-integr ated intensity (TII) due to the angularly dispersed BBW beam is consis tently smooth, regardless of the amount of propagation modulation or s elf-focusing growth present in the instantaneous profile. Similarly, t he angular dispersion will produce a time-dependent deflection of any amplitude modulation on the beam produced by laser defects. Because th e focus of the modulation is enlarged due to the deflection, the TII o f this amplitude structure is found to be less than that for a monochr omatic beam.