Nanomilling surfaces using near-threshold femtosecond laser pulses

We have produced crater depths of less than 10 nanometers using 100-1000 pulses of a near-infrared femtosecond laser (800 nm, 125 fs) on a copper thin film surface. By determining the single-shot ablation threshold, incubation coefficient and surface reflectivity, the femtosecond laser pulse parameters for surface nanomilling are established close to the multiple-pulse ablation threshold limit for a copper thin film. Photomultiplier measurements of a copper emission line were used as a real time monitor of the nanomilling process for which photons were detected only once every several shots. The results are consistent with a model that ablation occurs in bursts every several shots after a number of intervening incubation energy storage shots.