A mode converter for electron vortex beams is described. Numerical simulations, confirmed by experiment, show that the converter transforms a vortex beam with a topological charge m=±1 into beams closely resembling Hermite-Gaussian HG(10) and HG(01) modes. The converter can be used as a mode discriminator or filter for electron vortex beams. Combining the converter with a phase plate turns a pl...

Most of the reported vortex beam generators generate beams at a fixed frequency, which limits practical applications. Therefore, it is inevitable to explore generator, can actively control operating frequency. We propose switchable frequency terahertz metasurface, freely under single-frequency mode and dual-frequency by changing external temperature, phase state vanadium dioxide (VO<sub>2...

The Kelvin–Benjamin variational principle has been previously used to predict that vortex ring pinchoff can be delayed if the energy of the leading vortex ring is decreased during formation and/or the energy delivered by the vortex generator is increased. We present experimental results in which the former and latter energy effects were simultaneously accomplished by imposing a bulk axisymmetri...

We investigate, by numerical simulation, the shear layer instability associated with the outer layer of a spiral vortex formed behind an impulsively started thin ellipse. The unstable free shear layer undergoes a secondary instability. We connect this instability with the dynamics of corner vortices adjacent to the tip of the ellipse by observing that the typical turnover time of the corner vor...

In this paper, high order LES has been conducted for investigation on the flow around micro vortex generator (MVG) at Mach number 2.5 and Reθ=5760. The mechanism of vortex ring generation behind MVG, especially in the initial stage of the ring generation has been studied in detail. The results show that the ring structures come from both the sheer layer on the upper boundary of momentum deficit...

An analytical model describing laminar vortex ring formation in a nozzle flow generator piston/ cylinder arrangement proposed previously by the authors is extended to time-dependent velocity programs. The predictions of the model are in good agreement with the available numerical data for impulsive, linear, and trapezoidal velocity programs. We also show that properly scaled vortex circulation ...

A novel method to generate and manipulate vector vortex beams in an integrated, ring resonator based geometry is proposed. We show numerically that a ring resonator, with an appropriate grating, addressed by a vertically displaced access waveguide emits a complex optical field. The emitted beam possesses a specific polarization topology, and consequently a transverse intensity profile and orbit...