To reduce the use of fossil fuels, the adoption of battery electric vehicles (BEVs) using lithium-ion batteries has been increasing in internal combustion engine alternatives. Accordingly, significant efforts have been made to improve the manufacturing process of lithium-ion batteries within electric vehicles. In particular, the cutting process of lithium-ion batteries has been actively discussed as it is closely related to battery performance. Laser-based cutting enables a more precise and sustainable manufacturing process. The laser ablation threshold has been investigated in many studies to achieve high-precision laser processing. While laser parameters and ambient conditions have been examined to determine the laser ablation threshold, studies focusing on the effect of relative humidity remain insufficient. Thus, this study investigated the laser ablation threshold of aluminum foil under varying relative humidity conditions. First, a laser interaction chamber was fabricated to control the relative humidity during experiments. A scanning electron microscope (SEM) was then used to observe laser ablation craters and analyze the threshold. The variation of the laser ablation threshold with relative humidity revealed changes in the interaction between the laser and aluminum foil depending on the humidity level.

A femtosecond laser is used in various fields such as microscale machining, OLED repair, micro 3D structure fabrication, and eye surgery. Particularly, because of non-thermal property, ablation and ablation threshold are the most representative characteristics of femtosecond laser. The ablation system is accompanied by many optics, stage, or gantry. In the case of the gantry, an ordinary optic system delivers a beam where mirrors and lens are required. If the gantry moves to the sample, external stimulation such as vibration will occur. Vibration has an influence on optics such as transforming beam path and becomes an error that decreases accuracy, precision, and spatial resolution. Generally, Fiber Optic Beam Delivery System (FOBDS) is used to solve this issue. But in the case of the femtosecond laser, FOBDS is incompatible. Recently, another FOBDS model that is compatible with the femtosecond laser has been developed. In this paper, the ablation threshold was obtained by FOBDS and femtosecond laser. The results present a possibility of ablation without external stimulation.