Appl Opt. 2023 May 1;62(13):3409-3415. doi: 10.1364/AO.487898.
Measurement of the topological charge (TC) of vortex beams, including integer and fractional orbital angular momentum, is of great importance in diverse fields. Here we first investigate the diffraction patterns of a vortex beam from crossed blades with different opening angles and positionings on the beam by a simulation and experiment. Then the positions and opening angles of the crossed blades that are sensitive to the variation of TC are selected and characterized. We show that for a specific position of the crossed blades on the vortex beam, the integer TC can be measured directly by counting the bright spots in the diffraction pattern. Moreover, we show experimentally that for other positions of the crossed blades, by calculating the first-order moment of the intensity of the diffraction pattern, the integer TC between -10 and 10 can be obtained. In addition, this method is used to measure the fractional TC and, as an example, the TC measurement is demonstrated for a range between 1 and 2 with 0.1 steps. The result of the simulation and experiment shows good agreement.
测量涡旋光束（包括整数和分数轨道角动量）的拓扑电荷（TC）在各个领域都具有重要意义。在这里，我们首先通过模拟和实验研究了具有不同开口角度和位置的交叉刀片对光束的衍射图案。然后选择和表征了对 TC 变化敏感的交叉刀片的位置和开口角度。我们表明，对于涡旋光束上交叉刀片的特定位置，可以通过计数衍射图案中的亮点直接测量整数 TC。此外，我们通过实验表明，对于交叉刀片的其他位置，通过计算衍射图案强度的一阶矩，可以获得 -10 到 10 之间的整数 TC。此外，该方法还用于测量分数 TC，并且作为一个例子，展示了用于 1 到 2 之间的 TC 测量，步长为 0.1。模拟和实验结果吻合较好。
