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. New results concerning the scaling of the production process using a high repetition rate laser and a fast translation stage are demonstrated. The cross-sections of the ripples are investigated using electron microscopy. A very large aspect ration of ~10 is observed for the periodical nanostructures in fused silica. Using in-volume selective laser etching (ISLE) of sapphire results in deep hollow nanoplanes ~200 nm in width and up to 1 mm in length. Microchannels have been produced using in-volume selective laser etching with a scanning speed of 1 mm/s.