应用光学, 2017, 38 (5): 831, 网络出版: 2017-10-12  

利用光斑图像特征确定飞秒激光有效烧蚀焦距

Effective ablation focus determination of femtosecond laser by using spot image feature
作者单位
1 华北理工大学 电气工程学院,河北 唐山 063009
2 卡尔加里大学 机械及制造工程系,阿尔伯塔 卡尔加里 T2N 1N4
3 北京科技大学 自动化学院,北京 100083
摘要
为确定飞秒激光光束对微尺度结构的烧蚀深度,研究了给定功率条件下对应的激光束有效烧蚀焦距。提出采用激光焦点处获得的烧痕阵列图像及在离焦状态下提取烧痕图像特征,通过分析图像特征与离焦距离,获得激光束有效烧蚀焦距范围的方法。在激光束焦点附近的硅晶片表面烧蚀出斑痕阵列,向下逐渐减小焦距,采集硅晶片斑痕图像,提取斑痕平均像素面积及斑痕目标与背景之间的R分量灰度差,获得斑痕像素面积及灰度差随激光束焦距变化的曲线;向上逐渐增大焦距,提取并获得斑痕像素面积及灰度差随激光束焦距变化的曲线。结合激光束向下离焦阈值(633 μm)及向上离焦阈值(993 μm),确定20 mW输出功率条件下,飞秒激光在硅晶片材料表面的有效烧蚀深度为360 μm。采用中位值方法确定了激光束在硅晶片表面聚焦时的焦距为0.823 mm。实验表明,激光烧蚀斑痕像素面积及灰度差与激光束焦距之间的关系能够客观地反映激光束有效烧蚀焦距的变化范围。
Abstract
In order to determine the influence of femtosecond laser machining center on ablation depth with micro-scale structure , the effective ablation focal length of laser beam corresponding to the given power was researched,a method for getting the ablated spot array image at laser focus ,extracting the image feature in defocus stage and obtaining the effective ablation focus range of laser beam by analyzing the relationship between the image features and the defocus distance was proposed. Firstly,the spot array was ablated on the surface of silicon wafer near the laser beam focus. Secondly, the focal length was gradually reduced downward to capture the spot image of silicon wafer, the average pixel area of spot image and the gray difference of R component between spot target and background were extracted, and the change curves of spot pixel area and gray difference with focal length of laser beam were obtained. Again, the focal length was gradually increased upward , the change curve of spot pixel area and gray difference with focal length of laser beam was extracted and obtained similarly . Finally, combined with the downward defocus threshold (633 μm) and upward defocus threshold (993 μm) of laser beam, under the condition of 20 mW output power, the effective ablation depth of femtosecond laser on silicon wafer surface was determined to be 360 μm. By using median value method, the focal length on the surface of silicon wafer was determined to be 0.823 mm while defocused. Experimental results show that the relationship among spot pixel area, gray difference and laser beam focal length can objectively reflect the variation range of effective ablation focal length of laser beam.

王福斌, 刘同乐, 武晨, 胡连军, 陈至坤, Paul Tu. 利用光斑图像特征确定飞秒激光有效烧蚀焦距[J]. 应用光学, 2017, 38(5): 831. Wang Fubin, Liu Tongle, Wu Chen, Hu Lianjun, Chen Zhikun, Paul Tu. Effective ablation focus determination of femtosecond laser by using spot image feature[J]. Journal of Applied Optics, 2017, 38(5): 831.

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