USP Laser micro-machining in high fluence regimeTuesday (23.06.2020) 17:00 - 17:20 Room 1
Micro-machining with femtosecond laser is widely developed for texturing different materials to create functionality or engrave patterns. Nowadays, more powerful ultrafast lasers are coming on the market. Such high power is directly linked with the repetition rate and the pulse energy of the laser, respectively opening the way to higher productivity by either machining with high beam velocity and with high beam energy density. In this work we focus on the second case of high fluence regime. It is known that above a critical power, nonlinear effects appear in air. We experimentally define this threshold in terms of critical fluence by measuring the energy before and after the focus position.The experimental threshold is measured to be between 2.5*10^13 W/cm2 and 7.8*10^13 W/cm2. The theoretical intensity for such effects in air is at least 10^13 W/cm2. The measured threshold is consistent with the order of values found in the literature. We have studied the effects of such high intensities on the machining around this threshold on tungsten and other metals with different energies. When the laser interacts with metals at low peak intensity, the hole is uniform following a logarithmic law. If the intensity increases, a second concentric hole appears in middle of the impact. The theoretical diameter without nonlinear effects of air is plotted. At low energies, the outer measured diameters are in good agreement whereas above a peak intensity of 3.9*10^13W/cm², the measured diameter increases defining the threshold of the apparition of non-linear effects. In addition, the theoretical size of the affected areas according to the peak intensity is equal to the size of the second concentric hole appearing. That means that the nonlinear effects of air could play a role on the micromachining. This will be investigated on different materials.