From random to controlled small-scale filamentation in water.

Simple apertures such as slits and meshes inserted in the beam path of a powerful Ti:Sapphire laser pulse are suitable to produce stable 1-D and 2-D arrays of filaments in liquids. The thus imposed intensity gradients and diffraction patterns can overcome the inherent beam irregularities which naturally give rise to random small-scale multiple filamentations. This method is visualized by means of two photon fluorescence imaging.