部分相干环形光束经透镜聚焦的焦移和焦开关

Focal shift and focal switch of partially coherent annular beam focused by lens

为了从理论上对部分相干环形光束被透镜聚焦后轴上点的光强分布以及焦移和焦开关现象进行研究,采用惠更斯-菲涅耳衍射积分方法进行了理论分析,取得了轴上点光强分布及焦移、焦开关现象的相关数据。结果表明,焦移量不仅依赖于环形光束外半径的菲涅耳数,还依赖于入射部分相干光的空间相干度和中心拦截比。菲涅耳数越大,焦移量越小;部分相干光的空间相干度越高,焦移量越小。菲涅耳数一定时,环形光束的中心拦截比越大,焦移越大。对于某一固定的空间相干度,随着菲涅耳数的降低会出现焦开关现象。这些结果对研究部分相干环形光束的聚焦性质是有帮助的。

Applying the Huygens-Fresnel diffractive integral,the on-axis intensity distribution and the phenomena of focal shift and focal switch are theoretical studied when a partially coherent annular light is focused by a lens. The results show that the amount of the focal shift depends on not only the Fresnel number of the annular beam, but also the spatial coherence and the central obstruction ratio of the incident partially coherent light. It is also shown that the greater the Fresnel number, the smaller the focal shift; the higher the spatial coherence, the smaller the focal shift. For a fixed Fresnel number, the larger the central obstruction ratio is,the larger the focal shift is. For a given spatial coherence, the phenomenon of focal switch will occur as the Fresnel number decreases. The results are helpful to the research of the focus of partially coherent annular beam.