Ultrafast laser interaction with transparent multi-layer SiO2/Si3N4 films

We investigate the use of ultrafast lasers exposure to induce localized crystallization and elemental redistribution in amorphous dielectric multi-layers, composed of alternating Si3N4 and SiO2 layers of sub-micrometer thickness. Specifically, we report on the occurrence of a laser-induced elemental intermixing process and the presence of silicon nanocrystals clusters localized within the multi-layers structure. The spatial distribution of these clusters goes significantly beyond the zone under direct laser exposure providing evidence of energy being channeled transversely to the laser propagation axis at the interface of the nanoscale layers. Thanks to the extreme conditions reigning during laser exposure, this process transposed to various materials may offer a pathway for local and selective crystallization of a variety of compounds and phases, difficult to obtain otherwise.