Femtosecond pulse induced nanostructures in ULETM glass
We report on nanostructures induced by tightly focused ultrashort laser pulses in the bulk of ULE glass. These so-called nanogratings  consist of sheet-like cavities which arrange in periodic grating planes with subwavelength periodicity. Emerging after several laser pulses the grating planes are always oriented perpendicular to the laser polarization. So by combing the tunable orientation with the outstating three-dimensional writing ability allows for the fabrication of almost arbitrary phase elements .