Rasouli Saifollah, Gholami Azam, Amiri Pouria, Kotlyar Victor V, Kovalev Alexey A
J Opt Soc Am A Opt Image Sci Vis. 2022 Jul 1;39(7):1246-1255. doi: 10.1364/JOSAA.460772.
In this work, the far-field propagation of multi-vortex beams is investigated. We consider diffraction of a Gaussian wave from a spatial light modulator (SLM) in which a multi-fork grating is implemented on it at the waist plane of the Gaussian wave. In the first-order diffraction pattern a multi-vortex beam is produced, and we consider its evolution under propagation when different multi-fork gratings are implemented on the SLM. We consider two different schemes for the phase singularities of the implemented grating. A topological charge (TC) equal to is considered at the center of the grating, and four similar phase singularities all having a TC equal to =4 (or =-4) are located on the corners of a square where the singularity is located on the square center. Some cases with different values of , and consequently , are investigated. Experimental and simulation results show that if signs of the TCs at the corners and center of the square are the same, the radius of the central singularity on the first-order diffracted beam increases, and it convolves the other singularities. If their signs are opposite, the total TC value equals zero, and at the far-field, the light beam distribution becomes a Gaussian beam. For determining the TCs of the resulting far-field beams, we interfere experimentally and by simulation the resulting far-field beams with a plane wave and count the forked interference fringes. All the results are consistent.
在这项工作中,研究了多涡旋光束的远场传播。我们考虑高斯波在空间光调制器(SLM)处的衍射,其中在高斯波的腰平面上实现了多叉光栅。在一阶衍射图样中会产生多涡旋光束,并且我们考虑当在空间光调制器上实现不同的多叉光栅时其在传播过程中的演化。我们考虑所实现光栅的相位奇点的两种不同方案。在光栅中心考虑一个等于 的拓扑电荷(TC),并且四个类似的相位奇点都具有等于 =4(或 = -4)的拓扑电荷,它们位于一个正方形的角上,而 奇点位于正方形中心。研究了一些具有不同 值以及相应 的情况。实验和模拟结果表明,如果正方形角上和中心的拓扑电荷符号相同,一阶衍射光束上中心奇点的半径会增大,并且它会使其他奇点卷积。如果它们的符号相反,总拓扑电荷值等于零,并且在远场,光束分布变为高斯光束。为了确定所得远场光束的拓扑电荷,我们通过实验干涉以及模拟将所得远场光束与平面波干涉,并计算叉状干涉条纹。所有结果都是一致的。