# Experimental Study on Femtosecond Laser Processing Performance of Single-Crystal Silicon Carbide
## 1 Introduction  
Single-crystal SiC possesses many advantages, including outstanding optical properties, excellent thermal stability, high chemical inertia and high hardness. Owing to these features, it finds widespread applications in various fields, such as integrated circuits, solar cells and photoelectric detection, among others [1]. Fabricating micro/nanostructures on the surface of single-crystal SiC using traditional manufacturing technologies is challenging due to its difficult-to-machine property. However, femtosecond laser technology offers a powerful solution for the micro/nano fabrication of SiC materials. This method has advantages, such as high 3D-precision and non-invasive manufacturing characteristics [2]. The femtosecond laser processing technology, which has the advantages of three-dimensional high-precision and non-destructive processing, provides a technical means for the preparation of micro/nanostructures of single-crystal SiC [3, 4]. Based on the characteristics and application requirements of femtosecond laser machining, many scholars have conducted experimental research on femtosecond laser micro-machining [5, 6]. To fabricate grooves or ablation craters with low thermal damage, high aspect ratio, and MRR, commonly used methods include changing the processing environment or adjusting laser parameters, such as liquid assisted processing, selective chemical etching assisted processing and the temporal and spatial modulation of the beam. When machining grooves are fabricated in an ambient environment, the depth of material removal is mainlycontrolled via the optical penetration depth within the low fluence range [7]. With the increase in fluence and its pulse number, the interaction between pulses increases the absorption of materials to subsequent pulses, and the effect of heat accumulation on material removal cannot be ignored. However, cracks, fragments and recast layers appeared around the ablation crater [8]. In addition, pulse width and wavelength also have a certain impact on material ablation [9; 10]. When the pulse width is narrower and the peak fluence is higher, the enhanced ultrafast absorption of laser energy by the material is stronger, resulting in an increase in ablation depth. However, when the pulse width decreases to a certain value, the further reduction of the pulse width will lead to an increase in threshold fluence and the width of the groove will not change with the change of pulse width. When the laser wavelength is shorter and the photon energy is greater, the processing accuracy will be higher, the ablation depth will be greater and the ablation threshold will be lower [10]. In order to eliminate the recast layer and thermal damage introduced by femtosecond laser processing in the air environment, many scholars have adopted liquid assisted methods. The flow and volatilization of ethanol help further carry away the ablative debris, reduce the redeposition of ablative materials and facilitate the discharge of debris from the crater [11]. The ablation depth of ethanol assisted lithography is deeper than that of processing in ambient air, and ethanol-assisted lithography does not generate additional thermal damage around the crater. Distilled water assistance is also commonly used in the preparation of high surface quality grooves [12]. The underwater femtosecond laser processing method can effectively reduce the redeposition of debris in the surrounding area of the groove, thereby improving the processing quality. However, the uncertainty of laser-induced bubbles and material deposition limits the surface accuracy and processing efficiency of grooves. [PERSON] et al. [13] observed the femtosecond laser processing of underwater SiC ceramics using a high-speed camera and found that the disturbance degree of laser induced bubbles is closely related to the size, distribution and motion of the bubbles.