  Understanding of material behaviour at nanoscale under intense laser
excitation is becoming critical for future application of nanotechnologies.
Nanograting formation by linearly polarised ultra-short laser pulses has been
studied systematically in fused silica for various pulse energies at 3D laser
printing/writing conditions, typically used for the industrial fabrication of
optical elements. The period of the nanogratings revealed a dependence on the
orientation of the scanning direction. A tilt of the nanograting wave vector at
a fixed laser polarisation was also observed. The mechanism responsible for
this peculiar dependency of several features of the nanogratings on the writing
direction is qualitatively explained by considering the heat transport flux in
the presence of a linearly polarised electric field, rather than by temporal
and spatial chirp of the laser beam. The confirmed vectorial nature of the
light-matter interaction opens new control of material processing with
nanoscale precision.
