The experiment shows, when the background gas pressure is less than 400 Pa,a bright emission small sphere exists before the target surface, and the diameter of the sphere is much larger than the size of the laser ablated point.

• 实验发现 ,当背景气压为 40 0Pa以下时 ,在靶面上存在一个明亮的发光球体 ,球体直径远大于激光烧蚀斑的大小 ,此球体向四周辐射等离子体光谱 ,只是在垂直靶面的方向辐射相对较强。