Measuring High-Order Optical Orbital Angular Momentum With a Petal-Like Zone Plate

Orbital angular momentum (OAM) detection is a key technique in the applications of vortex beams. In this letter, we propose a simple method to flexibly determine the high-order OAM state of a vortex beam with a petal-like zone plate (PZP). It is theoretically demonstrated that the far-field diffraction of the product of vortex beam and PZP is a Hermitian-like form of the vortex beam. Therefore, the magnitude of the topological charges (TCs) as well as the sign of incident vortex beam can be read from the numbers and direction of the dark lines in the Hermite–like pattern. Possessing the multiple focusing characteristic, the Hermite-like pattern of detected vortex beam can be found in a range of distance instead of a certain location. Meanwhile, to promise a high detection efficiency, the key parameters of PZP have been studied in details. Experimental results agree well with the theoretical prediction. It is testified that the measured TCs can be up to 100.