Definition

Polarization ripples are parallel oscillations which have been observed since 1960's on the bottom of pulsed laser irradiation of semiconductors. They have the property to be very dependent from orientation of the laser electric field.

Since apparition of femtosecond laser, it has been observed on metals, semiconductors, but also on dielectrics.
Moreover, their periodicity on dielectrics with a large number of irradiation and small energy provide periodic structures with a period near 100 nm.

Formation mechanisms

The formation mechanisms are still under debate. However, two types of formation mechanisms can be underlined :

• the resonant mechanisms, which are based on electromagnetic aspects, as periodic energy deposition due to roughness , as plasmon excitation on surface, or wake plasmon excitation;
• the non-resonant mechanisms, more related with thermal consequences of the irradiation of the target by the laser, like capillary waves formed in the melted layer.

Applications

Their interest is about potential applications in building microfluidic channels, changing the color of materials , modifying local electrical properties , and building sub-diffraction-limit optical diffraction grating

Diffraction grating

In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...

s.

They also constitute the first stage of the Black Silicon

Black silicon

Black silicon is a semiconductor material, a surface modification of silicon with very low reflectivity and correspondingly high absorption of visible light. The modification was discovered in the 1980s as an unwanted side effect of reactive ion etching...

formation process by femtosecond irradiation.