聚焦异常空心光束的焦移

Focal shift in focused anomalous hollow beam

基于柯林斯衍射积分公式推导出了异常空心光束通过薄透镜聚焦后的解析表达式。运用导出公式,通过数值计算分析了异常空心光束聚焦区域的光强分布,并对异常空心光束的焦移特性进行了研究,详细讨论了光束有效菲涅耳数、光束形状和光腰位置对焦移的影响。研究结果表明:聚焦异常空心光束的轴上光强最大点不与几何焦点重合,而是偏离几何焦点。通过选择合适的光束参数和光学系统,异常空心光束将发生异常空心光束的焦移,其焦移量不仅依赖于光束有效菲涅耳数,而且依赖于光束椭圆率以及光束入射面与透镜的距离。

The analytical expression of the focused anomalous hollow beam（AHB） passing through a thin lens was derived based on the Collins formula.Using the derived formula,the irradiance distributions of an AHB in focal region were investigated,and the focal shift of focused AHB was studied in detail by numerical calculations.The effect on focal shift by the beam effective Fresnel number,the beam shape and the location of beam waist of the AHB were also discussed in detail.It is found,the position of the axial maximal irradiance of focused AHB is not coincident with the geometrical focus but is somewhat shifted away from the geometrical focusing point.The focal shift of the AHB takes place by a suitable choice of beam parameters and optical system,and the focal shift depends not only on the effective Fresnel number,but also on the ellipticity of AHB and the distance from the input plane to the lens plane.