After femtosecond laser micromachining the tooth surface, optical microscope dmm-300c was used to observe the characteristics of ablation ring morphology under different energy densities of 19 MJ / cm2, 31 MJ / cm2, 67 MJ / cm2 and 105 MJ / cm2, as shown in Fig. 1. It is found that with the increase of femtosecond laser energy, the ablation size characteristics of gear surface become more obvious. When the injection energy is 19 MJ / cm2, there is no obvious ablation phenomenon on the surface of the material; when the energy density increases to 31 MJ / cm2, the ablation area begins to form and the area gradually increases, and the diameter of the ablation circle is about 11 μ M. when the energy density reaches 105 MJ / cm2, the ablation area presents more obvious morphological characteristics, and the diameter of the ablation circle is about 23 The ablation area increases with the increase of energy density.
Scanning electron microscope Fei quanta 200 was used to observe the microstructure of ablation crater under different energy densities. As shown in Fig. 2 (a), when the energy density is 31 MJ / cm2, large particles are formed at the ablation crater, more molten substances are accumulated in the crater, and the inner wall of the ablation pit is uneven, the influence area near the ablation pit is large, and the ablation morphology near the whole ablation pit is relatively rough; when the energy density reaches 67 MJ / cm2, as shown in Fig 2 (b) shows that there are less particles formed at the ablation crater, no obvious accumulation is formed, the shape of the inner wall of the ablation pit is relatively flat, and the influence area near the ablation pit is small; when the energy density is 105 MJ / cm2, as shown in Fig 2 (c) shows that there is no obvious accumulation at the ablation crater, the influence range of the area near the ablation pit is smaller, and the inner wall of the ablation pit is smoother, and the ablation morphology near the ablation crater is relatively smooth. According to the above analysis, the energy density of laser input should reach the energy density ofgasification temperature, that is, the energy density should not be less than 67 MJ / cm2, which can ensure that the ablation area near to maintain good morphology characteristics during femtosecond laser processing.
The full view of the ablation crater and the morphology of the pit wall and pit bottom are shown in Fig. 3 (a) and (b) respectively when the laser energy density is 67 MJ / m2. It can be seen from Fig. 3 (a) that the ablation area of femtosecond laser is small, there are some mechanical scratches around, and the ablation pits are relatively flat 3 (b) it can be seen that there is no obvious spatter and molten substance on the side wall of the ablation pit, and the diameter of the inner ring of the whole ablation pit from the top to the bottom of the pit gradually decreases, which is caused by the normal distribution of Gaussian pulse energy, and the energy decreases gradually along the pit wall.