Generation of THz Vortex Beams and Interferometric Determination of Their Topological Charge

this article, we developed and demonstrated the efficacy of 3-D printed spiral phase plates (SPPs) for the generation of vortex terahertz (THz) beams with angular momenta P = +/- 1 and P = +/- 2. The vortex beam generation was confirmed by means of frequency-domain transmission spectroscopy. The topological charge P of the vortex beams was determined via phase-sensitive Mach-Zehnder interferometry, which enabled the superposition of a vortex beam with P and its conjugate beam with -P. The resulting interference patterns were found to be consistent with the expected intensity distributions for a given P, which provides strong confirmation of the spatial phase structure of the generated vortex beams in the THz regime.