Continuous wave laser ablation of alumina ceramics under long focusing condition

Abstract

The low laser absorption of ceramic materials makes continuous wave (CW) laser ablation require high peak power densities, however craters on the material surface have been shown to significantly improve its absorption, which opens new possibilities for CW laser processing of ceramic materials. In our experiments, we noticed that under long focusing condition (focal length of 500 mm, diameter of 170 μm, average power of 100–700 W), the CW laser power density, even after being reduced to 1 % (from 9 × 10⁷ W/cm² to 9 × 10⁵ W/cm²), was still able to achieve highly efficient ablation to alumina ceramic with the aid of craters prepared by the ablation of carbon particles on the material surface. More interestingly, 3 mm thick alumina ceramic could be transiently penetrated by the CW laser within an irradiation time of 20 ms, which showed a completely different ablation efficiency and mechanism from the conventional CW processing of ceramic materials. To this end, we comprehensively revealed the ablation characteristics and intrinsic mechanism of alumina ceramics under the ablation of the long focal condition CW laser through systematic process comparison experiments, high-speed shadow imaging, and theoretical simulation. The results can help to guide the CW laser processing of ceramic materials, such as high depth-width ratio hole processing, welding, etc., and also provide theoretical guidance for the design of ceramic-based high-energy laser protection materials.