Single- and Multi-Beam Drilling of Thin Titanium Foils by Femtosecond Laser Ablation in Liquids.

Ultrashort pulsed laser ablation is an excellent process for high precision micromachining of thin substrates across a broad range of solid materials. As a special application, this method is used in laser drilling to create functional surfaces, e.g. porous materials for filtration or electrodes for electrolysis. This study proposes a different physical alternative to conventional pulsed laser drilling by transitioning the process from a gaseous atmosphere to a denser and thermally more conductive liquid medium. To overcome physical limitations from a low plasma energy threshold and time-related impediments associated with pressure wave and cavitation bubble formation, this study explores different pulse energies at 1032 nm central wavelength with MHz and GHz burst technology and a combined process parallelization through multi-beam generation with a high-power spatial light modulator. Utilizing laser bursts, hole densities of 924 / mm² with diameters as small as 2 micrometers can be generated over large areas of up to 2500 mm². In combination with multi-beam processing, the effective drilling time can be reduced below 5 ms / hole for a total of 9 parallel beams. All tests were conducted on 25 micrometer thin foils of titanium grade 1, immersed in flowing deionized water. [ABSTRACT FROM AUTHOR]