Surface and bulk micro- and nano-structuring with nanojoule femtosecond laser pulses at high repetition rate

Sub-wavelength 3D- respectively 2D-structuring of borosilicate glass and polymer foil was performed using a special femtoTrain device (High Q Laser) emitting in the infrared at the intrinsic wavelength of 1028nm and also in the green at 514nm by means of SHG. The pulse duration is typically 200fs, whereas the applied low pulse energy in the nJ-range and the pulse repetition rate fixed at 20MHz. The samples were moved in three dimensions above the static laser beam by using a micromanipulator system to obtain groove-shaped structures in the surface and cylindrical bulk structures growing from the surface into the volume of the probes. The laser beam was focused using an oil immersion objective with a numerical aperture of 1.3. The diameters of 3D bulk structures are e.g. 7μm with an aspect ratio of 24:1. The widths of the surface-structures are smaller than the wavelength. The walls of the surface-structures are periodically superimposed by low scale ripples whose period length is about 20% of the laser wavelength or absolutely scaled in the sub-200nm range. The described laser setup can be considered as a novel tool for nanoprocessing in material science, nanobiotechnology, nanomedicine as well as security.