Diamond possesses high hardness, excellent thermal conductivity, and extremely high electron mobility. Cutting tools and microelectronic heat dissipation devices have high requirements for the quality of diamond microgroove structures. Therefore, achieving mass production, low-cost, and high-precision microstructure processing is a focus of current research. Compared with traditional diamond processing methods, ultrafast lasers cause the target material to detach from the ablation area in a gaseous or plasma state, which offers significant advantages, such as non-contact, good controllability, and a small heat-affected zone. However, owing to the extremely short pulse width of ultrafast lasers, the interaction mechanism between the laser and material is difficult to observe, and the physical phenomena in the laser-irradiated area are complex, which makes it challenging to ensure the resolution and controllability of diamond microgrooves. Therefore, studying the processing mechanism of ultrafast laser irradiation on chemical vapor deposition (CVD) diamond, analyzing the surface morphology of microgroove processing, and optimizing process parameters are of great significance.

This study reveals the interaction mechanism between ultrafast lasers and diamonds by establishing a finite element simulation model. Using an ultraviolet picosecond laser with a pulse width of 10 ps, laser wavelength of 355 nm, and maximum power of 10 W, microgrooves were etched on the surface of the sample. The dimension of the single-crystal CVD diamond sample was 7 mm×7 mm×1 mm. A shape measurement optical microscope system was used to observe the surface morphology and particle distribution of the microgrooves, whereas a confocal microscope was employed to observe the sample dimensions and defect characteristics. Based on the surface morphology characteristics of the diamond after laser processing, quality evaluation criteria were established for the picosecond laser processing of CVD diamond. A factor effect analysis was applied to the established evaluation criteria to determine the contributions of different process parameters, thereby ensuring the resolution and controllability of the diamond microgrooves.

In this study, a transient temperature field model is established to analyze the temperature field distribution under a single pulse. Grid independence verification shows that the grid is gradually refined when the grid size is smaller than 1/50 of the spot radius. Moreover, the maximum and minimum temperatures eventually stabilize (Fig. 3). In addition, under the action of 10 pulses, a repetition rate of 1000 kHz causes thermal accumulation more easily (Fig. 6). The results of a morphological analysis using a shape measurement optical microscope system reveal that the high-pressure airflow formed inside the microgrooves drives particles out of the irradiated area. The further the distance from the ablation area, the lower the airflow pressure is, and this causes particles to deposit outward, along the microgroove edges. At higher scanning speeds, high-temperature, high-pressure plasma formed on the diamond surface, causes ablation particles to fly out at high speeds, which results in a particle-free deposition area near the processing region (Fig. 7). The established quality evaluation criteria for CVD diamond laser cutting indicate that the size of the heat-affected zone (HAZ) is fixed under the same energy density (Fig. 10). The maximum outward extension distances of different types of defects within the HAZ are identical. When various defects appear in the microgrooves, the defects on one side of the microgroove are more significant than are those on the other side. This may be because of the offset angle generated between the center of the processing area and the center of the galvanometer during scanning leading to different thermal stresses at the micro-groove edges. The results of a factor effect analysis of the process parameters show that when using the microgroove width as the evaluation criterion, laser power has a greater impact on the microgroove width than does the scanning speed (Table 3). When the laser power is 6 W and the scanning speed is 10 mm/s, the interaction between the two factors reaches a minimum (Fig. 12). When using the HAZ width as the evaluation criterion, the scanning speed has a greater impact on the HAZ width than does the laser power (Table 4). When the laser power is 8 W and the scanning speed is 10 mm/s, the interaction between the two factors reaches a minimum (Fig. 14). The scanning number has a weaker effect on both the microgroove and HAZ widths (Fig. 13 and Fig. 15).

This study primarily presents simulation and experimental research on the picosecond pulse laser processing of CVD diamonds. The main conclusions are as follows.

1) When the grid size is smaller than 1/50 of the spot radius, the maximum and minimum temperatures no longer fluctuate significantly with a varying grid refinement.

2) High-temperature, high-pressure plasma affects surface particle deposition in different states and causes microcracks to form beneath the diamond surface.

3) The establishment of microgroove quality evaluation criteria shows that the HAZ size is fixed under the same energy density and that the maximum outward extension distances of different types of defects within the HAZ are the same.

4) When using the microgroove width as the evaluation criterion, the laser power has a greater impact on the microgroove width than does the scanning speed. When the laser power is 6 W and the scanning speed is 10 mm/s, the interaction between the two factors reaches its minimum. When using the microgroove HAZ width as the evaluation criterion, the scanning speed has a greater impact on the HAZ width than does the laser power. When the laser power is 8 W and the scanning speed is 10 mm/s, the interaction between the two factors reaches its minimum. The scanning number has a weaker effect on both the microgroove and HAZ widths.