Thermal imaging of high power ultrashort pulse laser ablation of alumina towards temperature optimized micro machining strategies

Abstract

The application of pulsed laser systems with pulse durations in the pico- and femtosecond regime for material processing is commonly associated with a cold ablation. Due to the minimized interaction-time between the ultrashort laser pulses and the material, this statement is almost valid as long as no heat accumulation effect appears. With the increasing demand of high productivity processes, the average power of ultrashort pulsed laser systems increases above 100 W, which leads, however, to increased thermal effects during laser processing. This is especially important for laser processing of technical ceramics like alumina. Large temperatures gradients, which locally occur during laser processing using high average power could lead to thermal modifications and cracks in the material. In this study, we present a process-optimization method for high power laser ablation of alumina based on thermal imaging. The use of a 2D IR camera enables the estimation of the temperature distribution during the laser processing. We investigate the influence of laser power up to 80 W, pulse duration between 900 fs and 10 ps and processing duration on the resulting material temperature. Beside the material temperature we evaluate the material removal rate and the resulting surface quality.