部分相干电磁光束的焦移

Focal shifts of focused partially coherent electromagnetic beams

基于有效菲涅耳数的概念,给出一种简单的表达式来评估部分相干电磁光束经圆形光阑透镜后所产生的相对焦移,对部分相干电磁光束经透镜聚焦的情况进行了研究。结果表明:当交叉谱密度函数的非对角元素为零时,有效菲涅耳数不仅依赖于真实的菲涅耳数大小,而且依赖于光束的偏振分布和入射部分相干电磁光束两个偏振分量的空间相干长度;相对焦移量仅由等效菲涅耳数决定。将此方法与数值积分法进行的比较表明,等效菲涅耳数可以简单、准确地评估焦移。

Based on the effective Fresnel number, a simple analytical expression is presented to evaluate the relative focal shift in a circular-aperture lens system which is illuminated by a partially coherent electromagnetic beam. The effective Fresnel number is dependent not only on real Fresnel number but also on the polarization distribution and spatial coherent lengths of two polarized components of the incident partially coherent electromagnetic beam. It is shown that the relative focal shift is just determined by the effective Fresnel number. The results indicate that this new method can evaluate the focal shifts simply and exactly.