Yuping Tai

In situ measurement of the topological charge of a perfect vortex using the phase shift method

We propose a method to determine the topological charge (TC) of a perfect vortex. With the phase shift technique, the perfect vortex and its conjugate beam exactly overlap and interfere. Consequently, the TC of a perfect vortex is determined by counting the number of interference fringes. This proposed method enables in situ determination of the TC of the perfect vortex without the need for additional optical elements, and it is immune to environmental vibration and parasitic interference.

Fraunhofer diffraction of Laguerre–Gaussian beam caused by a dynamic superposed dual-triangular aperture

Abstract. We investigate the Fraunhofer diffraction of a Laguerre–Gaussian (LG) beam incident on a dynamic superposed dual-triangular aperture. The evolution of the diffraction pattern from this aperture is analyzed experimentally and theoretically. A special aperture, called the hex-star triangular aperture, demonstrates interesting diffraction patterns. Further, the diffraction properties of integer, half-integer, and fractional orders of topological charges at the Fraunhofer zone are studied by using the hex-star triangular aperture. This study can provide additional information to enhance the understanding of the diffraction properties of the LG beam transmitted through a complex aperture.

Digital speckle correlation method based on phase vortices

A new digital speckle correlation method (DSCM) based on phase vortices is proposed in this paper. The complex signal is recon- structed by a Laguerre-Gauss filter applied to the original speckle pattern. Moreover, the pseudophase distribution is obtained. Each phase vortex position is then located, and its topology charge of þ1 or −1 is used to replace the values of the original elements in the pseudophase matrix, in which other elements occupy with zeros. Finally, two sparse matrices representing the speckle field before and after displacement are constructed, respectively. Using these two sparse matrices, correlated cal- culation is conducted. The results show that this method has the same precision as the traditional subpixel DSCM, while its resumption time is only one-tenth of that of the latter. It is also strongly robust to immune noise.

Close-packed optical vortex lattices with controllable structures

As a spatial structured light field, the optical vortex (OV) has attracted extensive attention in recent years. In practice, the OV lattice (OVL) is an optimal candidate for applications of orbital angular momentum (OAM)-based optical communications, microparticle manipulation, and micro/nanofabrication. However, traditional methods for producing OVLs meet a significant challenge: the OVL structures cannot be adjusted freely and form a close-packed arrangement, simultaneously. To overcome these difficulties, we propose an alternative scheme to produce close-packed OVLs (CPOVLs) with controllable structures. By borrowing the concept of the close-packed lattice from solid-state physics, CPOVLs with versatile structures are produced by using logical operations of expanding OV primitive cells combined with the technique of phase mask generation. Then, the existence of OAM states in the CPOVLs is verified. Furthermore, the energy flow and OAM distribution of the CPOVLs are visualized and analyzed. From a light field physics viewpoint, this work increases the adjustment dimensions and extends the fundamental understanding of the OVL, which will introduce novel applications.

Micro/nano displacement measurement using sub-pixel DSCM

A selection method of subset size in sub-pixel displacement registration is proposed. The algorithm principle of interpolation, fitting of distribution of the correlation coefficients and gradient-based methods are introduced. Using computer-simulated speckle images, their precision and efficiency depending on the subset size are studied. The optimal method and subset size are presented in various measurement ranges, which offer measuring bases for sub-pixel in DSCM.

Application of dynamic speckle method using in sedimentation process of silver chloride

The generation process of silver chloride was studied using dynamic speckle methods including speckle size measurement and speckle contrast measurement. The quantity and size changes of the sedimentation particles in the illuminating region were investigated and analyzed.