Ripples formation under femtosecond laser irradiation : mono and multi pulses studies and interpretation
Résumé
Femtosecond lasers have proved to be great tools for precise, accurate and high quality micro- but also nano- machining. Numerous works have been carried out to study laser-matter interaction mechanisms on the one hand, and laser machining processes on the other hand . Periodic surface structures, usually named ripples, are often presented in machined samples, either on the surface itself, or on the walls of grooves or holes [5]. Such structures have to be controlled with accuracy to improve processing quality. Sub wavelength ripples can be obtained both on metallic or dielectric samples, and such periodic nano structures can be used for surface functionalization and “smart” marking. The control of sample marking requires a good understanding of laser matter interaction mechanism. For femtosecond regime, the standard surface scattered wave model is not well suited and has to be refined using Maxwell equation boundaries taking into account the induced polarisation and resonant surface excitation calculation, using also a suited model to describe matter optical absorption.