Ultrafast laser micro-cutting of stainless steel and PZT using a modulated line of multiple foci formed by spatial beam shaping

Abstract

Femtosecond laser surface processing of materials allows for precise micrometer cutting with restricted detrimental side effects. An efficient way to increase the ablation or cutting speed and energy efficiency of the process is the generation of N parallel laser spots in the focal plane of a lens on the sample surface, each spot simultaneously following a defined cutting trajectory. However, the cutting scheme is then limited in area to avoid overlap of the spot trajectories. We present in this paper a technique to overcome this limitation. The ultrafast laser beam wavefront is spatially modulated, generating a line of multiple processing spots in the lens focal plane. Micro-cutting is then conducted by translation of the sample along the spot line. That way, no restriction on the cutting trajectory length is imposed while preserving the increase in the cutting speed and energy efficiency of the process compared to single spot machining. Successful cutting of PZT ceramic and stainless steel is achieved with the spot array and compared to single spot machining in terms of processing time. In the case of PZT, the cutting efficiency and speed is compared to single spot laser machining with various focal lenses. We also investigate the effect of intensity gradient on the spots line for micro-cutting on stainless steel. The method efficiency is discussed relying on surface characterization using scanning electron microscopy.