采用飞秒激光在金属材料表面制备周期性微结构在光伏发电、自清洁以及生物医学等领域具有广阔的应用前景。采用功率为75 W、脉宽为800 fs、波长为515 nm的飞秒激光,首先研究线扫描条件下钛的烧蚀阈值,然后基于90°交叉面扫描的加工方式诱导钛表面微结构,推导出面扫描时单位点的有效脉冲数计算公式,并对结构演变规律进行归纳分析。结果表明:同文献报道的红外飞秒激光相比,钛表面绿光飞秒激光的烧蚀阈值明显降低;不同参数对钛表面微结构的影响可以归纳为面扫描单位点的有效脉冲数和激光能量密度。当激光能量密度较低时,随着有效脉冲数的增加,钛表面微结构由不均匀分布的驼峰状凸起转变为均匀的柱状阵列结构,能量密度较高时则转变为相互连接的丘陵状结构。高的激光能量密度、低的有效脉冲数与低的激光能量密度、高的有效脉冲数诱导的结构类似,使用高能量密度可显著提高加工效率。

The femtosecond laser, which induces periodic microstructures on the surfaces of metallic materials, is extensively applied in photovoltaic power generation, self-cleaning, and biomedical fields. In this paper, we fabricate periodic microstructures on the surface of Ti by utilizing a green femtosecond laser with a power of 75 W, a pulse width of 800 fs, and a wavelength of 515 nm. First, the ablation threshold of Ti under the line-scan condition is discussed herein. The Ti surface microstructures are induced based on a 90° cross-surface scan processing. We derive the formula for the calculation of the effective-pulse number per unit point in the surface scanning and summarize the microstructural evolution. The results obtained demonstrate the following: 1) the ablation threshold of Ti by utilizing the green femtosecond laser is significantly lower than that of the previously reported long-wavelength infrared laser; 2) the surface microstructure of Ti can be attributed to the effective-pulse number per unit point and the laser fluence in the surface scanning. Due to the increase in the effective-pulse number, the microstructure changes from nonuniform distribution of hump to uniform columnar array structure when the laser fluence is low, or to interconnected hilly structure when the laser fluence is high. The similar structure can be obtained either by applying a high laser fluence and small effective-pulse number, or a low laser fluence and large effective-pulse number. The former can significantly increase processing efficiency.