Multiple filamentation induced by input-beam ellipticity

The standard explanation for multiple filamentation (MF) of intense laser beams has been that it is initiated by input beam noise (modulational instability). In this study we provide the first experimental evidence that MF can also be induced by input beam ellipticity. Unlike noise-induced beam breakup, the MF pattern induced by ellipticity is reproducible shot to shot. Moreover, our experiments show that ellipticity can dominate the effect of noise, thus providing the first experimental methodology for controlling the MF pattern of noisy beams. The results are explained using a theoretical model and simulations.