Zhaogang Nie

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.

Synthesis of single crystal α-Fe2O3 nanotube via facile route and discussion of formation mechanism

Abstract Single crystal α-Fe2O3 nanotube was synthesised via refluxing in the organic solvent of n-butylalcohol that employed Fe(OH)3 sol as precursor without any surfactant and dispersant. Then the final products were characterised by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. The XRD analysis confirmed trigonal crystal system α-Fe2O3 with high purity and good crystallinity, which were confirmed further by EDAX pattern. The TEM images displayed the morphology of α-Fe2O3 which was mainly nanotubes with outer diameters of 10–15 nm, inner diameters of 6–10 nm and length of 100–120 nm. The poly vinyl alcohol (PVA)–α-Fe2O3 nanocomposite obtained by doping the product in PVA showed a strong absorption both in UV and visible regions. Furthermore, the possible formation mechanism was proposed based on the experimental results, which revealed that the nanotubes were easily obtained in the interface of collide and n-butyl alcohol by the surface tension.