Mechanisms of damage formation in glass in the process of femtosecond laser drilling

Abstract

The development of femtosecond lasers has renovated micromachining technology, enabling the microdrilling of transparent materials at high speed. Although effective, this technique is still imperfect because irregular microscopic damage occurs during processing. Several factors in the formation of damage induced by a single laser pulse have been suggested; however, the entire mechanisms of damage formation in the process of drilling are not fully understood. Here we investigated the causes of microscopic damage both by experimentally carrying out laser drilling on chemically strengthened glass samples and by numerically analyzing the propagating stress wave and temperature distribution. We have revealed that the damage at the sidewall and bottom of a generated hole is mainly due to the stress wave, while the damage around the hole entrance is mainly due to relaxation of thermal stress. In particular, we have analyzed these processes quantitatively, demonstrating the time courses of the passage of the stress wave through the material and the temperature distribution generated by the excited electrons. Our analyses are useful in suggesting processing techniques, or suggesting glass materials suitable for laser drilling such as glass with high heat resistance, which may lead to an improvement in the quality of micromachining.

Direct observation of structure-assisted filament splitting during ultrafast multiple-pulse laser ablation

“…In the case of second pulse irradiation (N = 2), a distinct plasma filament splitting phenomenon was observed, which was evidently different from the first pulse-induced plasma (N = 1). The splitting phenomenon is similar to final crater shape in previous works [21,22] and needs to be further explained. The formation of the plasma filament for the first pulse (N = 1) was attributed to the self-focusing effect caused by the optical Kerr effect.…”

“…Photon-electron interaction is the first step of energy deposition during laser ablation [19] and is thus the most crucial step during multipulse ablation [20]. Some previous works have been carried out to investigate the mechanism of multipulse ablation in terms of numerical model and final damage structures [21,22]. However, few studies have focused on this dynamic behavior under multipulse irradiation; moreover, the related mechanisms have not been completely elucidated.…”

Design and Fabrication of Bulk Micromachined 4H-SiC Piezoresistive Pressure Chips Based on Femtosecond Laser Technology

“…Femtosecond laser has been proved to be an effective method for SiC pressure sensor diaphragm fabrication among them [ 32 , 33 , 34 ]. However, for brittle materials, the microscopic damage accumulated on the diaphragm caused by the stress wave during femtosecond laser processing is still inevitable [ 35 , 36 ]. Therefore, the laser parameter combination is worth studying to meet the requirement of low-damage and smooth-sensor diaphragms preparation.…”

Laser Microdrilling of Slate Tiles

“…Above a threshold irradiance, cracks are almost avoided. Ito et al investigated the damage mechanisms leading to the formation of cracks during femtosecond laser microdrilling of glass [12]. These mechanisms are related to thermal stresses in the hole entrance and to stress waves in the hole walls and exit.…”