用衍射方法确定平顶光学涡旋拓扑荷数

A Diffraction Method to Determine the Numbers of Flat-topped Optical Vortex Topological Charges

使用一种中心对称的正方形振幅光栅,分别计算了不同拓扑荷数的平顶涡旋光束经过不同空间频率的正方形振幅光栅后的夫琅和费衍射光场.结果表明,平顶涡旋光束经正方形振幅光栅后在远场的光强分布为亮斑阵列;选择合适的空间频率,即可以得到任何拓扑荷数的清晰的衍射图样;当拓扑荷数≥2时,衍射光强图样外围亮斑的个数为入射涡旋光束拓扑荷数的2倍.用此种衍射方法可以方便地测量入射光学涡旋的拓扑荷数.

The optical diffraction fields of flat-topped vortex beams possessing different topological charge values are theoretically calculated, through square amplitude gratings which have different spatial frequency. The results show that the distribution of diffraction intensity are bright spot array in the far field. If choosing appropriate grating spatial frequency, the diffraction pattern of different topological charge values could be obtained clearly. The numbers of bright spot surrounding diffraction patterns are double of the numbers of vortex beams topological charge. Using this diffraction method,the numbers of optical vor- tex topological charge can be measured conveniently.