Manufacturing of periodical nanostructures by fs-laser direct writing

Sub wavelength ripples (spacing < λ/4) perpendicular to the polarisation of the laser radiation are obtained by scanning a tightly focused beam (~1μm) of femtosecond laser radiation from a Ti:Sapphire laser (τ =100fs, λ =800nm & 400nm, f=1kHz) and from a Yb:glass fiber laser (τ =400fs, λ =1045nm, f=0.1-5MHz) over the surface of various materials like amorphous Nd:Gd3Ga5O12 films 1 μm in thickness on YAG substrates, diamond, polytetrafluoroethylene, LiF, MgF2, ZBLAN, Al2O3, LiNbO3, SiO2, Si, Cu and Au. The ripple patterns extend coherently over many overlapping laser pulses and scanning tracks. Investigated are the dependence of the ripple spacing Λ on the material, the lateral distance of the laser pulses, the N.A. of the focussing optics, the repetition rate and the applied wavelength. The ripples are characterised using electron microscopy. Some possible models for the origin of the ripple growth are discussed and conditions under which these phenomena occur are contained. New results concerning the scaling of the production process using a high repetition rate laser and a fast translation stage are demonstrated. Potential applications are presented and consequences for precise nano- and microstructuring using ultra short pulsed lasers are discussed.