Femtosecond laser nanostructuring in porous glass with sub-50 nm feature sizes.

We report on controllable production of nanostructures embedded in a porous glass by femtosecond laser direct writing. We show that a hollow nanovoid with a lateral size of ~40 nm and an axial size of ~1500 nm can be achieved by manipulating the peak intensity and polarization of the writing laser beam. Our finding enables applications ranging from direct construction of 3D nanofluidics in glass to clean stealth dicing of transparent plates.