# Gorilla Glass Cutting Using Femtosecond Laser Pulse Filaments
## 3 Materials and Methods
### Experimental Details  
The experiments were carried out using a femtosecond laser system (Cyber Laser Inc., Tokyo, Japan; IFRIT-LH-C031) having \(\lambda\) of 786 nm, pulse width (\(\tau\)) of 183 fs, and pulse repetition rate (\(R_{p}\)) of 1 kHz. Figure 3 illustrates the concept of the proposed femtosecond laser pulse filament-assisted Gorilla glass cutting technology and associated experimental setup.  
The concept of the proposed femtosecond laser pulse filamentation technique is visualized in Figure 3a. Using the proposed technique, we fabricated periodic micro-voids inside different layers of the Gorilla glass samples under variable laser energy. Two  
Figure 3: Proposed femtosecond laser pulse filaments assisted glass cutting technology and corresponding experimental setup. (**a**) Concept of the proposed technology; (**b**) mechanical cleaving process; (**c,d**) experimental setup: (**c**) schematic diagram, (**d**) photograph.  
different kinds of achromatic objective lens have been considered to focus the laser beam inside Gorilla glass samples: 50\(\times\) (Mitutoyo, Kanagawa, Japan; M Plan Apo NIR) having a numerical aperture (NA) of 0.42 with working distance (\(d\)) of 17 mm; 100\(\times\) (Mitutoyo, Kanagawa, Japan; M Plan Apo NIR) with NA = 0.7 and \(d\) = 10 mm. The laser energy and beam polarization were controlled using an integrated attenuator and linearly polarized beam splitter (Newport, Irvine, CA, USA). A rotation capable quartz phase \(\lambda\)/2 wave plate, connected with the beam splitter, transmitted the p-polarized beam for micromachining. On the contrary, we blocked the s-polarized beam, reflected at an angle of 90\({}^{\circ}\). The amount of power was attenuated from the computer by controlling the rotation angle of the circular power attenuator. We measured the laser power by placing a power meter (Coherent, Santa Clara, CA, USA; FM/GS) slightly below the focus position of the achromatic objective lens. Later on, the laser power values were converted to laser energy.  
To characterize femtosecond laser pulse filament-assisted periodic micro-voids inside the Gorilla glass samples, we varied various irradiation conditions of the laser beam. For the 50\(\times\) objective lens, the laser energy ranged between 25 and 50 uJ. In contrast, for the 100\(\times\) objective lens, the laser energy was in the range between 25 and 37 uJ. Furthermore, the focus position from the top surface of the sample glasses was varied from 100 to 600 uJ for 50\(\times\) objective lens and 50 to 470 uJ for 100\(\times\) objective lens. Figure 3c depicts the schematic diagram of the experimental setup. During laser micro-machining, the Gorilla glasses were placed on top of a 3-axis computer-controlled linear translation stage (DCT Linear Motor, Osan-si, Gyeonggi-do, Republic of Korea; LSC-0080-YF) having 100 nm resolution in the x, y, and z directions (Figure 3d).  
In order to cut 0.5 mm thick Gorilla glass, we tested with different combinations of laser energy (\(E\)), focus position from the top surface of the glass (\(f\)), and scanning speed (\(S\)) of the laser beam. The value of \(E,f\), and \(S\) were varied from 100 to 210 uJ, 50 to 200 uJ, and 1 to 3 mm/s, respectively. Consequently, a long filament array was engraved at the filament position (\(P\)). The micro-voids incorporated glass samples had undergone mechanical cleaving process to cut the glass samples into two pieces, where uniform mechanical pressure of 400 MPa was applied on both sides of the micro-channel (Figure 3b). The femtosecond laser pulse filaments and quality of glass cutting were examined under an optical microscope (ZEISS, Oberkochen, Germany; Axioskop 40).