# Experimental Study on Femtosecond Laser Processing Performance of Single-Crystal Silicon Carbide
## 1 Introduction
When small bubbles aggregate into large bubbles and adhere to the bottom or side wall of the groove, it greatly affects the reflection, refraction and scattering of the laser beam. Due to the limitations of underwater processing, many scholars have combined femtosecond laser processing with selective chemical etching methods to process SiC. After processing the surface of the workpiece material with femtosecond laser, a mixture of hydrofluoric acid and nitric acid is used for the selective chemical etching of the laser modified area. Craters can be fabricated on the workpiece material, and the chemical composition around the craters is the same as that of the unprocessed surface, without introducing impurities [14]. In addition to craters, grating structures can also be prepared on the surface of workpiece materials using femtosecond laser processing combined with chemical etching methods [15]. Changing the characteristics of the laser beam is also a commonly used measure to improve the processing effect. To improve processing efficiency and consistency, a diffractive optical element is used to divide a laser beam into five laser beams [16]. A single scan can obtain five uniform laser induced modified regions with similar morphology. Then, the materials of these modified regions are etched with hydrofluoric acid to form a micro-groove array, which increases processing efficiency by five times and obtains high aspect ratio grooves. In addition, when the laser intensity is higher than the ablation level, the Gaussian beam will be nonlinear distortion, and the Bessel beam can resist this instability. Therefore, Bessel beams are more suitable for groove machining with high aspect ratios [17]. The changes in the processing environment also have a significant impact. When the ambient pressure drops, the ionization effect of the air weakens, the depth of erosion increases and the sediment around the erosion crater is less [18]. When using etching gas and nitrogen gas for material processing, rough surface quality can be formed on the material, while in a vacuum environment, relatively good surface quality can be obtained [19]. As the ambient pressure increases, the collision between plasmas increases,resulting in an increase in energy reaching the material surface and an increase in ablation depth. However, the number of splashes on the sample surface increases. When the environmental pressure continues to increase, due to the obstruction of environmental gases and dense plasma, the processing depth decreases and the splashes on the surface of the workpiece will decrease [20]. In order to further understand the femtosecond laser processing performance of single-crystal silicon carbide and obtain a low thermal damage, high aspect ratio and high MRR, it is essential to conduct experiments on the femtosecond laser processing of silicon carbide micro-grooves. Hence, in the present study, experimental research was conducted on the feasibility of femtosecond laser processing of single-crystal SiC. Based on previous research [21; 22], this paper conducts single factor experiments and significance analysis to investigate the femtosecond laser processing of grooves of SiC. The effects of laser parameters, such as laser fluence, scan speed, repetition rate and multi-pass scanning on the depth, width, HAZ width and side wall inclination angle of the grooves, are discussed. Experimental methods for improving the aspect ratio and surface quality of grooves are discussed and the significance of the experimental results is analyzed.