## 1 Introduction
Their results demonstrated the advantages of underwater laser processing over conventional laser processing. [PERSON] et al. [PERSON] et al. (2018) processed silicon wafers via a flowing underwater laser composite etching process. To study the effects of underwater laser etching, they controlled the rate and direction of the water flow in a closed water chamber. With a high water flow rate, the grooves were deepened and few re-agglomeration layers were formed. The etching effect was superior to that obtained in still water. [PERSON] (2018) combined the parameters of laser water jets with those of hard and brittle processing materials and significantly improved the quality of the cut. [PERSON] et al. [PERSON] et al. (2018); [PERSON] et al. (2018) compared the surface morphologies of samples prepared via hybrid laser-water jet micromachining, traditional silicon processing, and laser composite processing technologies. They varied the processing parameters and analyzed their effect on the heat-affected zone and processing quality. [PERSON] et al. [PERSON] et al. (2018) established a fluid dynamics model based on smoothed particle hydrodynamics experimentally investigated the water-jet-assisted laser cutting of silicon materials. Experimental analysis revealed that the laser ablation of silicon mainly occurs via explosive melting. [PERSON] et al. [PERSON] et al. (2018) established a numerical model of heat transfer and material ablation in the water-jet-assisted laser etching of single-crystal germanium. They reported that the irradiated material can be discharged through the water jet and that during the non-pulsing periods, the water-jet cooling effectively removes heat buildup in the workpiece, thereby minimizing the thermal damage caused by laser heating. They also analyzed the influence of the processing parameters on the ablation process. Increasing the laser pulse energy deepened the grooves, whereas increasing the applied water pressure reduced the threshold workpiece temperature for material removal. [PERSON] et al. [PERSON] et al. (2018) established a three-dimensional analytical model of the temperature field during the hybrid laser water-jet micromachining process. Their model considers the interaction between the laser, water jet, and workpiece. The absorption of laser light by the water, the formation of laser-induced plasma in water, the formation of bubbles, and the laser refraction at the air-water interface were discussed. To evaluate two machining methods, [PERSON] et al. [PERSON] et al. (2018) compared the direct and chemical-assisted picosecond laser prerunning of single crystalline silicon. In their study, an orthogonal test design scheme was adopted to consider the relevant parameters affecting the preanning process. They found that the direct laser trepenning results are associated with significant thermal defects, whereas the chemical-assisted method can process microholes with negligible thermal damage. Conventional gas-assisted laser processed materials have defects such as a large heat-affected zone and many re-casting layers. Compared with traditional gas-assisted laser processing, the laser processing area is cooled and impacted by the water jet. Specifically, during laser processing, the water jet cools the material and its impact can wash away the slag and recast a layerafter laser processing. The cooling action can reduce excess heat acting on the surface of the material, reduce the heat-affected zone, and reduce the generation of microcracks, thereby improving the surface quality of the material. In this paper, water jets with different angle and velocities were used to assist laser etching of polysilicon. Previously, we studied the effect of different water jet velocities on the processing grooves when the water jet angle was 30\({}^{\circ}\)[19]. However, to the best of our knowledge, the effects of changing both the water-jet angle and velocity on the depth and width of the etched grooves have not been investigated.