Abstract

Recently there has been increased emphasis on spatial instabilities, especially in cavities.¹ Here we present a spatial instability, free from longitudinal feedback, in which a beam propagating in one direction in a self-focusing medium breaks up into more and more filaments as the input power is increased. These cell-exit patterns are stable and highly reproducible, showing that they are seeded by fixed phase variations across the input profile. A small-scale self-focusing approach (simulations using a perfect Gaussian input profile with random fluctuations) yielded output patterns with, at most, two or three filaments that fluctuated from run to run, in disagreement with experiment. However, by including the small inherent fixed-phase variations, we reproduced the experimental patterns and bifurcation routes. Consequently, even larger aberrations were intentionally introduced. The instability of this phenomenon is emphasized by the slowness (on the order of 1 s) with which the reproducible pattern is regained after the beam is momentarily interrupted.

© 1991 Optical Society of America