Research Projects

Project
"Dynamics of Laser-Induced Periodic Surface Structures" (DYLIPSS)

Summary

The present evolution in laser-induced processing technology is dictated by the development of precise processing tools that can structure materials with high degree of accuracy. This essentially requires establishing of new processing technologies on micro and nanoscale. A recent surge of interest in nanostructured materials stems from the remarkable effects that arise from the so-called "Laser-Induced-Periodic-Surface -Structure" (LIPSS), namely periodic surface structures arranged on sub-micron scale. Interesting properties (with applications such as optics, electronics, tribologics…) occur as we increase the dimensions by varying the topology from a practically smooth surface to a system composed of a periodic arrangement. Self-organization of nanoscale surfaces with application in wettability, laser marking and color coding for counterfeiting, are several examples of this kind. Alongside an ample fundamental effort to unravel the so far elusive formation mechanisms is performed worldwide. In line with these efforts, we propose an investigative approach with dual characteristics: a dynamical study of primary excitation mechanisms with the potential to interrogate present hypothesis, secondly a laser control approach is proposed in order to significantly improve the quality of surface structures.

The project is based on a franco-romanian collaboration with expertise in material design by laser engineering. The partnership has recently started in the framework of Bilateral Cooperation Egide Program "Brâncusi". Building on this, an approach is proposed in the work packages to improve functionalities to surfaces by laser nanostructuring. Numerous studies have demonstrated the capabilities of ultrashort laser pulses to perform ripples on surface and in the bulk of a large class of materials. A strong sensitivity to laser polarization is noted supposedly due to plasmonic responses but this hypothesis fails to explain all the different observed behaviours. Several questions and issues remain concerning the wavelength, the orientation and the contrast dependence of the surface pattern on laser parameters, and the incubation effects. They are still to be solved to optimize the properties of such periodically ordered systems. A better understanding of all of the different mechanisms (laser coupling, excitation, and self-arrangement) is needed to control ultra-fast laser action by the appropriate choice of material properties and laser parameter. The objectives of this 3 year program are to improve our knowledge on their mechanisms of formation to allow us to figure out the ultrafast irradiation conditions to achieve more desired pattern.

Transient optical properties, plasmonic and capillarity effects will be probed in order to adapt the temporal characteristics of the laser excitation, to the material response. At the end, the challenge will be to develop a fast and reproducible nanostructuring process, and to found the limits of such technique in terms of smaller size structure, high contrast and highest accuracy. The proposal intends to first develop a time-resolved in-situ evaluation means for laser-induced optical change and thermal effects. A second line of research includes the fundamental aspect deriving from the plasmonic coupling, the electron-phonon nonequilibrium stage, the subsequent sequence of phase transformation and finally the surface dynamics via surface tension gradients. A pachet of numerical simulations of the resulting laser effect based on Quantum Molecular Dynamics and hydrodynamic approach will accompany the study.

Engineering aspects by temporal design of laser fields to control the material excitation and the "self-organization" of nanoscale surfaces will be considered at the end of the project. Further steps will be taken into transforming these evaluation/control means into high resolution pulse shaping devices that can be implemented in industrial environments.