Femtosecond laser high-efficiency drilling of high-aspect-ratio microholes based on free-electron-density adjustments.
We studied the micromachining of high-aspect-ratio holes in poly(methylmethacrylate) using a visible double-pulse femtosecond laser based on free-electron-density adjustments. Hole depth and aspect ratio increased simultaneously upon decreasing the wavelength in the visible-light zone. When the pulse energy reached a high level, the free-electron density was adjusted by using a double-pulse laser, which induced fewer free electrons, a lower reflectivity plasma plume, and more pulse energy deposition in the solid bottom. Thus, the aspect ratio of the hole was improved considerably. At a moderate pulse energy level, a 1.3-1.4 times enhancement of both the ablation depth and the aspect ratio was observed when the double-pulse delay was set between 100 and 300 fs, probably due to an enhanced photon-electron coupling effect through adjusting the free-electron density. At a lower pulse energy level, this effect also induced the generation of a submicrometer string. In addition, the ablation rate was improved significantly by using visible double pulses.
Lan
L
Jiang
Juqiang
J
Fang
Qiang
Q
Cao
Kaihu
K
Zhang
Peng
P
Wang
Yanwu
Y
Yu
Qiang
Q
Huang
Yongfeng
Y
Lu
D007834:Lasers; D008422:Materials Testing; D019904:Polymethyl Methacrylate / Q000737:chemistry* / Q000528:radiation effects*; D016062:Porosity / Q000528:radiation effects; D011829:Radiation Dosage; D013499:Surface Properties / Q000528:radiation effects
D019904:Polymethyl Methacrylate