Polarization ripples

Polarization ripples are parallel oscillations which have been observed since the 1960s [1] on the bottom of pulsed laser irradiation of semiconductors.

Since the wide availability of femtosecond lasers, such structures have been observed on metals, semiconductors, but also on dielectrics.

Moreover, the ripples can reach far sub-wavelength periodicities until 100 nm as recently observed in titanium.

[7] An extension of the mechanism was also proposed to account for the development of periodic structures with periodicity larger than the laser beam's wavelength (i.e. grooves) that are formed perpendicularly to the subwavelength-sized ripples; the proposed physical mechanism assumes the erasing of periodic energy deposition followed by the formation of hydrothermal convection rolls that propagate parallel to the electric field polarisation.

[8] The analogy of the structure shape with the solution of Kuramoto-Sivashinsky equations is often mentioned to support different theories such as defect accumulation,[9] or ultrafast modification of the atomic lattice.