Evolution of Vector Vortex Beams Formed by a Terahertz Laser Metal Resonator

Abstract

Analytical expressions for the nonparaxial mode diffraction of a terahertz laser metal waveguide resonator are obtained. The study assumes interaction between the modes and a spiral phase plate, considering different topological charges (n). Also, using numerical modeling, the physical features of the emerging vortex beams as they propagate in free space are studied. The Rayleigh-Sommerfeld vector theory is employed to investigate the propagation of vortex laser beams in the Fresnel zone, excited by the modes of a metal waveguide quasi-optical resonator upon incidence on a spiral phase plate. In free space, the spiral phase plate for exciting TE11 mode from the profile with the intensity maximum in the center (n = 0) forms an asymmetric ring one with two maxima (n = 1, 2). For the exciting TE01 mode, the initial ring (n = 0) structure of the field intensity is transformed into a structure with a maximum radiation intensity in the center (n = 1), and later again into a ring (n = 2). The phase front of the beam for the Ey component of the linearly polarized along the y axis TE11 mode changes from spherical to spiral with one on-axis singularity point. In the phase profile of the transverse components of the azimuthally polarized TE01 mode, a region with two and three off-axis phase singularity points appears.