A focus automatic positioning system of high-power laser beam based on plasma ultraviolet radiation
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摘要: 精准定位激光束焦点位置是提高激光雕刻、切割、焊接等加工精度的重要基础，而传统测量方法不适用于自动寻找强激光焦点。基于激光烧蚀金属后等离子发光含大量紫外谱线的原理，以日盲的氮化镓肖特基光电二极管为传感器，设计了以304不锈钢靶材为耗材的红外强激光束自动寻焦方法及其装置。该方法与共聚焦显微镜检测平均烧蚀坑深的方法相比，当以脉冲宽度100 ns、重复工作频率20 kHz、平均功率10 W的1064 nm光纤激光雕刻机为实验对象时，二者定焦位置相差24 μm。Abstract: Accurate focus positioning of a laser beam is an important basis for improving laser engraving, cutting and welding accuracy, but the traditional methods are not fit for automatically finding high-power laser focuses. The plasma caused by laser ablating metal is able to emit a large amount of ultraviolet radiation. Therefore, in this paper a focus automatic positioning method for high-power infrared lasers is proposed and the relevant device is fabricated with a GaN Schottky photodiode as sensor and a 304 stainless-steel laser target as consumable material. As a contrast experiment, the depths of the laser ablation pits on the stainless-steel target are measured with a confocal microscope to find the deepest pits. The focal position difference is 24 μm between the two positioning methods, when the experiments using a 1064-nm-wavelength fiber laser engraving machine with a pulse width of 100 ns, a repetition frequency of 20 kHz and an average power of 10 W.
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Key words:
- high-power laser /
- focus /
- ultraviolet radiation /
- plasma /
- GaN
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图 1 自动寻焦系统的结构示意图
Figure 1. Structure schematic diagram of laser-focus automatic positioning system
图 4 紫外辐射信号的采集和放大电路原理图
Figure 4. Circuit schematic diagram of ultraviolet-radiation signal acquisition and amplification
图 6 不锈钢、铝和铜靶材的1064 nm激光烧蚀辐射强度对比
Figure 6. Comparison of stainless steel, aluminum and copper targets in ablative radiation intensity with 1064-nm-wavelength laser
图 7 基于两种方法所得定焦位置的对比
Figure 7. Comparison of laser focus positions based on two measurement methods
图 8 用共聚焦显微镜测量激光烧蚀深度
Figure 8. Laser ablation depth measurement using a confocal microscopy
图 9 GUVA-S12SD光电二极管光电响应特性曲线
Figure 9. Photoelectric response characteristic curve of GUVA-S12SD photodiode
图 10 激光平均功率与输出电压峰值的关系
Figure 10. Relationship of laser average power and output voltage peak
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