# Groove Formation in Glass Substrate by a UV Nanosecond Laser
## 1 Introduction  
The importance of glass as an engineering material is found in various fields of the industry. The high optical transparency and excellent dielectric property of the glass make it a suitable material for many optical and electrical applications. In addition, it has been widely used in biomedical areas owing to good chemical and thermal stability. Commonly, the processing techniques (diamond [1], roll [2], and wheel cutting [3]) using a physical contact of tool bits were used to machine glass materials. However, these conventional methods generally produce random cracking and rough-cut surfaces in material. Moreover, the precision machining of the glass with these methods is very difficult. A laser technique is greatly attractive in the processing of brittle glass materials because of its non-contact nature [4]. It can also provide a precise and clean process in a fast and automated way. Over the past several decades, many researchers have studied laser-based glass processing. In the early days, a CO\({}_{2}\) laser attracted great attention in the glass cutting process because the absorption rate of the CO\({}_{2}\) laser beam with 10.6 \(\upmu\)m wavelength is very high in glass materials. However, in most cases, glass processing by the CO\({}_{2}\) laser beam involves a large thermal effect that induces various defects such as cracking, chipping, and heat affected zone (HAZ) [5; 6; 7; 8]. This may require extra time and cost for cleaning and polishing of the cut-surface after the processing. The advent of ultra-short pulse lasers brings diverse applications to the area of glass processing [9; 10; 11; 12; 13; 14]. The pulse width of an ultra-short pulse laser ranges from picoseconds to femtoseconds. This enables the ultra-short pulse process to have an extremely short characteristic time scale compared with that for thermal diffusion, generally shown in a relatively long pulse or continuous wave (CW) laser process. Therefore, in the case of the ultra-short pulse process, the thermal effect can be minimized. In addition, the interaction between the high intensity beam of the ultra-short pulse laser and material usually induces multi-photon absorption and the avalanche ionization process [15; 16], which can enhance the absorption rate of the laser beam in glass materials. Because of these merits, the usage of the ultra-short pulse laser in glass processing is increasingly expanding. However, the cost per output power for the ultra-short pulse laser is still expensive. An ultraviolet (UV) laser, which has relatively high price competitiveness, may be adoptable in some applications of glass processing instead of the ultra-short pulse laser. The UV laser beam with a photon of high energy has a similar absorption mechanism to an ultra-short pulse laser. Moreover, it can also reduce thermal effects, with the pulsed mode generating a high peak power. Glass cutting with a UV laser was reported previously [17]. The UV laser of 355 nm wavelength was successfully used to drill holes in a soda lime glass of 1 mm thick and cut borosilicate glass of 200 \(\upmu\)m thick with no visible micro-cracks. [PERSON] et al. [18] reported glass processing by a UV nanosecond and infrared (IR) femtosecond laser. It was found that the surface roughness of grooves produced by the UV (266 nm) nanosecond and IR (800 nm) femtosecond laser was similar for borosilicate glass. However, for fused silica, the UV laser generated a very rough surface morphology owing to the presence of plasma and very low absorption of the UV beam in the fused silica glass. [PERSON] et al. [19] studied the micro structuring of silica glass surface with a UV laser at 266 nm. Well-defined micro-patterns were successfully formed on the glass surface without micro-crack and debris. [PERSON] et al. [20] demonstrated micro-channel scribing in borosilicate glass with a UV (255 nm) nanosecond laser. Burr-free channel edge was obtained through the optimization of process parameters; however, micro-cracking was occasionally produced at the channel junctions.