Femtosecond Laser Surface Texturing of Materials for Various Applications

Nforneh, Benjamen (2013-04-23)


Femtosecond lasers represent an electromagnetic field with field intensities approaching and even exceeding atomic binding field. When irradiated on a target, the material responses change from linear to nonlinear within a very short time. In most situations nonlinear absorption dominates and can be used in micro-machining of materials. In this work, analytical formulae are outlined relating laser and target parameters. This permits prediction of ablation conditions of materials. Ions are pulled out of a target due to charge separation caused by escaping electrons in the ablation layer which have acquired sufficient laser energy. In most cases the escaping electrons have energies equal or greater than the sum of the work function and the binding energy of the lattice. Additionally, the mechanisms of femtosecond laser melting, spallation and phase explosion of a titanium target are investigated using cascade simulations where the radiation event is modeled using molecular dynamics (MD) simulation combine with two temperature model (TTM). The model accounts for the electron heat conduction in the metal target and provide an adequate representation of the fast heating and cooling of the surface regions of the target. It uses the well-known TTM to represent heat transfer through and between electronic and atomic subsystems. The ablation yield is established for different laser fluences and the temperature evolution of the system identified. We conclude with a chapter that looks at two applications of femtosecond laser textured surfaces precisely in the photo-optics industry and in medicine.