The standard explanation for multiple filamentation of laser pulses is that
it is caused by noise in the input beam. We propose an alternative explana
tion that is based on deterministic vectorial (polarization) effects. We pr
esent numerical simulations in support of the vectorial-effects explanation
and suggest a simple experiment for deciding whether multiple filamentatio
n is due to vectorial effects. (C) 2001 Optical Society of America.