Optimization of ultrafast axial scanning parameters for efficient pulsed laser micro-machining

[Display omitted] •A tunable acousto-optofluidic lens is used to scan over the laser axial direction.•Oscillation in ablation depth is related to axial scanning amplitude and frequency.•An extended effective machining range is demonstrated experimentally.•Line machining parameters are optimized for uniform machining depth.•Multiple-pass groove machining is improved for both focused and defocused surfaces. In order to achieve high-resolution micro-machined features, tight focusing is traditionally adopted in laser micro-machining systems, at the cost of a narrow axial machining range. As the laser energy is confined in a single, fixed focal spot, machining throughput is significantly constrained by the writing speed of either translation stages or galvanometer scanners. We study an ultrafast axial scanning technique that asynchronously distributes laser pulses along the axial direction. Oscillation of the focal spot induced by the tunable acoustic gradient index lens is visualized in borosilicate glass with femtosecond laser pulses. By tuning frequency and amplitude of the acoustic field, machining parameters can be optimized, as demonstrated by the case of line machining on silicon. Multi-pass groove machining with axial scanning on silicon as well as femtosecond laser cutting of battery separators exhibit an extended effective machining range and an improved machining efficiency for both focused and defocused surfaces.