# Groove Formation in Glass Substrate by a UV Nanosecond Laser
## 2 Experimental Details  
The laser system (EVLASER Co., Ltd., Gyeonggi-do, Korea) used in this study consists of a UV (355 nm) Nd:YVO\({}_{4}\) laser source (INNGU LASER, Pulse 355-3A) and scanner module. The fundamental wavelength of the Nd:YVO\({}_{4}\) is 1064 nm. However, in this study, the Nd:YVO\({}_{4}\) laser with third-harmonic generation is used to give a laser beam of 355 nm wavelength. The Nd:YVO\({}_{4}\) laser has a pulse width of 12-22 nanoseconds and is operated at a 30-80 kHz pulse repetition rate. The pulse width information at various pulse repetition rates is shown in Table 1. A laser beam generated from the laser source is delivered onto the scanner. The laser scanner has a galvano mirror system and f-theta lens (110 mm \(\times\) 110 mm scan filed), so that it can move the laser beam of uniform intensity on a workpiece in fast and precise way. The effective focal length of the f-theta lens is 160 mm, and this gives a focused beam spot size of \(\sim\)20 \(\upmu\)m on the workpiece. In this experiment, the direction of the laser beam polarization is horizontal to the surface of glass. The schematic diagram of the UV nanosecond laser processing is shown in Figure 1. In this study, the experiments using both single laser scan and multiple laser scans are carried out. The multiple laser scanning methods used in the experiment are presented in Figure 2.  
Laser scans are also carried at various laser average powers. In this study, the laser average power is measured using the digital laser power meter with a thermal head detector (ADM-1000, lasermet, Bournemouth, UK) before the grooving experiment. During the measurement of the laser power, a defocused laser beam continuously moves along the circular track with a 3 mm diameter on the detector (to avoid damage of the detector) until the laser power value displayed is stabilized. The stabilized power value is used as a process condition.  
In this work, soda lime glass from a local supplier is used for laser processing. The thickness of the soda lime glass used in the experiment is \(\sim\)1.1 mm. The material properties and chemical composition of the soda lime glass are listed in Tables 2 and 3, respectively. The surface morphology of the laser-irradiated glass substrates is analyzed by an optical microscope (Dino Lite, AM4013 MZT) and a field emission scanning electron microscopy (FE-SEM, TESCAN MIRA LMH).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Pulse Repetition Rate (kHz)** & **Average Power (W)** & **Pulse Width (ns)** \\ \hline
30 & 4.06 & 12 \\
40 & 3.87 & 14 \\
50 & 3.58 & 16 \\
60 & 3.38 & 18 \\
70 & 3.18 & 20 \\
80 & 2.97 & 22 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Pulse width of the Nd:YVO4 (355 nm) laser at different pulse repetition rates (data from INNGU LASER).  
Figure 1: Schematic diagram of the laser grooving experiment.  
Figure 2: Multiple scanning methods. Method 1 indicates multiple laser scans with zero-scan spacing. Methods 2 and 3 are for multiple laser scans with non-zero scan spacing. In methods 2 and 3, 1 and 2 denote a scan sequence (1) is the first part of the scan sequence).