Results of the work in the Laser4Fun project has been published as:
L. Capuano, D. de Zeeuw and G.R.B.E. Römer. Towards a Numerical Model of Picosecond Laser-Material Interaction in Bulk Sapphire. JLMN-Journal of Laser Micro/Nanoengineering Vol. 13, No. 3, 2018
Crystalline sapphire (Al2O3) is a hard and transparent material widely used in industry. When applying IR laser wavelengths, sapphire can be laser-processed inside the bulk (sub-surface) to produce 3D structures, which can find uses, for example, in the production of microfluidic devices. Ultrashort and tightly focused laser pulses trigger several energy absorption mechanisms inside the bulk. The absorbed energy locally modifies the structure of sapphire. Existing (numerical) models of sapphire laser processing describe mainly femtosecond pulsed laser-material interaction (most of them only addressing surface processing) and, in addition, these models do not simulate the laser-induced temperatures of the lattice. Therefore, this study is aimed at a 2D-axisymmetric, time dependent, numerical model of the physics in picosecond laser-material interaction with sapphire. The physical phenomena in model include, but are not limited to: multiphoton absorption, tunneling ionization, avalanche ionization, recombination of carriers, diffusion of carriers and heat diffusion. Based on these phenomena, three quantities are calculated, namely: electron density, electron temperature and lattice temperature. The model was implemented in COMSOL Multiphysics®. It was found that, sapphire is modified by the laser radiation only if avalanche ionisation is triggered in the bulk.