In certain range of defocusing distance, if laser intensity is high enough, the expansion of irradiated area by laser beam can make the radial keyhole size synchronously increase with laser spot.

• 离焦量在一定的范围内,在足够高的激光能量密度下,激光辐照范围的增大使得小孔径向尺寸与激光光斑同步变化。