# Gorilla Glass Cutting Using Femtosecond Laser Pulse Filaments
## 4 Results and Discussion
### Cutting Gorilla Glass Using Femtosecond Laser Pulse Filament-Assisted High Aspect Ratio Micro-Voids  
The longest filaments we achieved during the filament characterization experiments were 146 \(\upmu\)m for a 100\(\times\) objective lens with the laser energy of 37 \(\upmu\)J and focus position of 470 \(\upmu\)m. Filaments of 146 \(\upmu\)m are insufficient for a single cut of a 0.5 mm thick Gorilla glass. Thus, we require increasing the micro-voids' length, which was achieved by increasing the laser energy and decreasing the scanning speed. We tested several combinations of laser energies, focus positions, and scanning speeds. We utilized a 100\(\times\) objective lens and varied the laser energy, focus position, and scanning speed from 100 to 210 \(\upmu\)J, 0 to 200 \(\upmu\)m, and 1 to 5 mm/s, respectively. As a result, we were successful in forming long filaments suitable for single cut of 0.5 mm thick Gorilla glass samples. Figure 8 shows the optical microscope images of the top surface (top view), bottom surface (top view), and cut surface (side view) of the Gorilla glass samples under different irradiation conditions of the laser beam. At first, a femtosecond laser with energy of 210 \(\upmu\)J was focused on the top surface of the Gorilla glass and scanned at a velocity of 5 mm/s. As a result, an \(\sim\)8.2 \(\upmu\)m wide micro-grove was formed on the top surface of the glass (Figure 8a). Because of the absence of Kerr medium between the objective lens and the focal point, no filaments was formed inside the glass. As a result, the bottom surface of the micro-groove was clearly evident in Figure 8a. Afterwards, we focused the laser beam (\(E=210\)\(\upmu\)J) only 50 \(\upmu\)m inside the Gorilla glass and scanned the beam at a scanning speed of 2 mm/s. Still, the filament length was long enough to reach the rear surface of the 0.5 mm thick Gorilla glass (Figure 8b). A periodic micro-void array with a period of 2 \(\upmu\)m was observed at the rear surface of  
Figure 7: Filament position and length under variable laser energy for 100\(\times\) objective lens. the glass. The width of the micro-groove, formed on the rear surface of the glass, was \(\sim\)3.3 \(\upmu\)m. Afterwards, the same laser beam was focused 100 \(\upmu\)m inside the Gorilla glass and irradiated at a scanning speed of 1 mm/s. As a result, the filaments were overlapped and a straight micro-channel having a width of \(\sim\)2.05 \(\upmu\)m was formed inside the glasses from the focal point of the laser beam to the rear surface (Figure 8c). The dark color of the micro-groove confirmed the formation of a micro-channel in the laser irradiated plane. Subsequently, the laser beam was focused 200 \(\upmu\)m inside the Gorilla glass sample and the translation stage was moved at a velocity of 1 mm/s. As a result, a 1.9 \(\upmu\)m thick high aspect ratio micro-channel was formed inside the glass sample, as shown in Figure 8d. Furthermore, we tested three other combinations to cut the 0.5 mm thick Gorilla glass using a single time laser irradiation. Case 1: \(E=150\)\(\upmu\)J, \(S=3\) mm/s, \(F=100\)\(\upmu\)m (Figure 8e); Case 2: \(E=100\)\(\upmu\)J, \(S=2\) mm/s, \(F=100\)\(\upmu\)m (Figure 8f); and Case 3: \(E=210\)\(\upmu\)J, \(S=1\) mm/s,  
Figure 8: Optical microscope images of the top surface, bottom surface, and cut surface of the micro-voids engraved Gorilla glass samples under variable irradiation conditions of the femtosecond laser beam.