Simulation of terahertz pulse with orbital angular momentum induced using spiral phase plate

Abstract

A silicon spiral phase plate (SPP) was proposed for a pulsed terahertz signal to produce orbital angular momentum with a topological charge of l = 2. The resulting field distribution after the signal passes through the SPP was simulated using the finite-difference time-domain method and observed at different propagation distances. It shows that the double-helical spatial structure and optical vortex were best observed at the farthest distance of 7.5 cm. Additionally, the output of a source with different central frequencies was observed when using the same SPP and still showed a hollow distribution indicating structured light but with two distinct vortices near the center.