Ablation enhancement by defocused irradiation assisted femtosecond laser fabrication of stainless alloy

We evaluate the effects of the holes geometry drilled by a femtosecond laser on a stainless alloy with various defocused irradiation time, which ranges from 0 min to 1 h. The laser ablation efficiency is increased by a factor of3 when the irradiation time is elevated from 0 to 30 min. Also, the morphology of the hole is observed by a scanning electron microscope, where the result indicates that the defocused irradiation time has a significant influence on the morphology changes. The reason for such changes is discussed based on the pretreatment effect and the confined plasma plume. As an application example, the microchannel is fabricated by a femtosecond laser combined with the defocused irradiation to demonstrate the advantage of the proposed method in fabricating functional structures.     

Femtosecond laser highly-efficient plane processing based on an axicon-generated donut-shaped beam

A simple technique is proposed for highly-efficient plane processing fully based on femtosecond laser beam shaping. The laser intensity distribution is transformed from a Gaussian to a donut shape. As the donut-shaped focus seems like a flat top from the side view, a plane with a high level of flatness is obtained directly by scanning once.By applying it to polishing experiments, the surface roughness can be improved significantly. The influence of scanning speed, laser pulse energy, and scanning times on the roughness is also discussed. Moreover, the scanning width can be flexibly controlled in a wide range.