Polarization ripples

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.

The set of resonant mechanisms leading to formation of ripple is defined by the strong link between ripple periodicity and laser wavelength. [Guosheng, Bonch-Bruevich]. It includes the excitation of surface electromagnetic wave such as surface plasmon polariton, and surface waves excited by a isolated defect or surface roughness. [Derrien 2011]

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 gratings.

They also constitute the first stage of the Black Silicon formation process by femtosecond irradiation.

External links

• example.com