## 3 Results and Discussion
### Optical Experimental Setup and Results  
The experimental setup for the mirror-based scanning system uses two galvanometers, including a femtosecond laser source (CB3-40-0200-10-H, Light Conversion, Vilnius, Lithuania) [38], a beam expander (BEX 1x-8x, Jenoptik, Jena, Germany), and a galvanometer scanner AVG14 HPO, Aerotech Inc., Pittsburgh, PA, United States). The carbide ultrafast laser we used is a femtosecond laser system with a high repetition rate based on a chirped pulse amplification technique (CPA). Its active operating environment is generated using directly diode-pumped Yb: KGW (ytterbium-doped potassium gadolinium tung-state). The laser head consists of a Kerr lens mode-locked oscillator (OSC), stretcher compressor (SC), and regenerative amplifier (RA) units. Automated harmonics modules are used to convert fundamental laser radiation to be with specific harmonics, and a third harmonic of 343 nm is selected in this study. The laser system has high beam quality, in which the roundness of the input beam laser profile is over 96%. There is also a beam quality M2 of 1.05 and a divergence angle of 0.31 mrad. Based on the concept of this approach, all laser sources could be suitably applied. Compared to the visible and infrared spectral regions, our study decided to select a UV laser because it has the smallest spot size and a higher absorption rate of materials. A UV laser could do the most multilayer structure processing without the limitation of material type. The femtosecond laser source was equipped with a third harmonic generation module emitting at a wavelength of 343 nm, with a pulse duration of 210 fs, beam quality factor M\({}^{2}\) < 1.1, and a repetition rate of 200 kHz, to create a raw laser beam with a diameter of approximately 2.0 mm and beam ellipticity of 95.4%. A galvanometer scanner housing was designed for a 1D scanner using two galvanometers, in combination with an f-theta lens (S4 LFT4125/075, Sill Optics GmbH & Co. KG, Wendelstein, Germany) with a focal length of 125 mm, which was used for deflection and the focusing of the laser beam. The scanning range of the f-theta lens is up to 2809 mm\({}^{2}\), with a working distance of 156.905 mm. The overall optical setup is illustrated in Figure 9. The raw laser beam will be enlarged three times by a beam expander. The experimental design was conducted to compare a 2D galvanometer scanner and the optimized 1D galvanometer scanner using two galvanometers. The geometry value of via holes is collected and analyzed by VK-X200 (Keyence, Osaka, Japan) [39] in the range of \(\pm\)25 mm from the center position of the workpiece. Figure 8: **(a)** Simulation results comparing the roundness of ablations of the 1D scanning system using two galvanometers in the red circle and the 2D scanning system in the blue square, in which the cyan line shows the roundness of ablations in ISO 11145:2018. **(b)** The compensation of telecentricity in the 1D scanning system using two galvanometers compared to the conventional 2D scanner. Figure 9: **(a) Overall view of experimental setup from computer-aided design (CAD) model for a 1D scanning system using two galvanometers and beam profile of laser source and laser beam after passing through beam expander. (b) Schematic representation of laser setup for conjugated two galvanometers to minimize telecentricity, 1D scanning system using two galvanometers with a distance between the two mirrors of 1 = 40 mm. **  
In this study, a raw laser beam diameter of d\({}_{\rm o}\) = 2.0 mm was measured by Thorlab's high-magnification zoom lens system. The system includes an 8-megapixel C.C.D. camera for microscopy S805 MU1, 12X zoom lenses MVL12X3Z, 12X system magnifying lens attachments MVL12X20L, and extension tubes for the 12X system MVL20 FA, mounted next to the galvanometer scanner.