Femtosecond laser written nanostructures in Ge-doped glasses.

We report on nanostructures induced by femtosecond laser pulses in the bulk of Germanium-doped silica glasses. For studying structural properties of the nanostructure constituents small-angle x-ray scattering and SEM served to map pore size, filling factor and periodicity. Our results show that with increasing the Ge doping concentration, the aspect ratio (transverse to inscribing laser) of nanometric pores rises while they arrange in a smaller period in contrast to nanogratings in pristine fused silica. Consequently, higher optical retardance can be obtained demonstrating the pronounced glass decomposition due to the changing network structure.