Kumar Praveen, Nishchal Naveen K
J Opt Soc Am A Opt Image Sci Vis. 2019 Aug 1;36(8):1447-1455. doi: 10.1364/JOSAA.36.001447.
This study demonstrates a self-referenced interferometric method to estimate the magnitude and sign of a high-order topological charge (TC) carried by incoming optical vortex beams. The proposed method uses a right-angle prism in a Mach-Zehnder interferometer setup with controlled lateral shift and tilt between the wavefronts of interfering beams. The in-line interference with its conjugate results in a petal-shaped fringe pattern, where the number of petals reveals the magnitude of the TC. When the direction of one of the interfering beams is laterally displaced and rotated to emerge at a small angle for off-axis interference such that the vortices overlap at the output plane, then a fork-like interference pattern with better visibility is obtained, which can be used for estimating the magnitude as well as the sign of the TC. Through numerical simulation and optical experiment, it is shown that the technique is capable of estimating the TC of Laguerre-Gaussian beams even with a nonzero radial index.
本研究展示了一种自参考干涉测量方法，用于估计入射光学涡旋光束所携带的高阶拓扑电荷（TC）的大小和符号。所提出的方法在马赫-曾德尔干涉仪设置中使用直角棱镜，在干涉光束的波前之间具有可控的横向位移和倾斜。与共轭光的同轴干涉产生花瓣状条纹图案，其中花瓣的数量揭示了TC的大小。当其中一束干涉光束的方向横向位移并旋转，以小角度出射进行离轴干涉，使得涡旋在输出平面重叠时，可获得具有更好可见度的叉状干涉图案，该图案可用于估计TC的大小和符号。通过数值模拟和光学实验表明，该技术即使对于非零径向指数的拉盖尔-高斯光束也能够估计其TC。
