  Femtosecond laser micromachining provides high precision and less thermal
diffusion in surface structuring as a result of the ultrashort temporal
duration and ultrahigh peak intensity of the femtosecond laser pulses. To
increase the throughput of surface patterning, the focal spot size can be
expanded with loose focusing, which, however, could lead to nonlinear
self-focusing of the pulses when the pulses propagate in air. We solve the
problem by use of spatiotemporally focused femtosecond laser pulses for
ablation of metal surfaces, which gives rise to improved surface quality as
compared with that obtained with the conventional focusing scheme.
