Generation of THz Vortex Beams and Interferometric Determination of Their Topological Charge
Samuel W. Pinnock, Seulki Roh, Tobias Biesner, A. V. Pronin, Martin Dressel
Abstract
In 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell = \pm 1$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell = \pm 2$</tex-math></inline-formula> . The vortex beam generation was confirmed by means of frequency-domain transmission spectroscopy. The topological charge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> of the vortex beams was determined via phase-sensitive Mach–Zehnder interferometry, which enabled the superposition of a vortex beam with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> and its conjugate beam with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-\ell$</tex-math></inline-formula> . The resulting interference patterns were found to be consistent with the expected intensity distributions for a given <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> , which provides strong confirmation of the spatial phase structure of the generated vortex beams in the THz regime.