Heat accumulation effects during ultrashort pulse laser ablation with spatially shaped beams

Ultrashort pulse (USP) lasers are widely used for milling, drilling and cutting applications. Their main advantages are the ability to process a broad range of different materials as well as allowing high precision ablation and yield of low surface roughness. However, until now relatively low volumetric ablation rates are obtainable for the USP milling processes. In the present study, we concentrate on the prediction of the shortest processing time required to ablate a specific geometry in a specific body. For that we discuss possibilities to increase the ablation rate for the application of laser milling of metals. Pulse energy, repetition rate and focal beam size are defined as free parameters of the ablation process thus controlling the ablation rate. The heat accumulation effect in the bulk material and reaching of a critical, material specific surface temperature are assumed to be the limiting factors for the indefinite increase of the ablation rate. An analytical model for heat accumulation during USP laser ablation of geometrically limited bodies is extended to be applied to the process with spatially shaped beams. The thermal limit of the ablation rate is determined by means of the developed model. In order to further develop the process strategy of laser beam stamping, demand for new beam shaping systems and laser sources with high pulse energies is derived from the simulation results.