PROPAGATION OF VECTOR VORTEX BEAMS EXCITED BY A TERAHERTZ LASER DIELECTRIC RESONATOR

Abstract

In this paper, analytical expressions for the nonparaxial mode diffraction of a terahertz laser dielectric waveguide resonator are derived. It is assumed that the modes interact with a spiral phase plate. The cases of different topological charges (n) are considered. Also, using numerical simulations, the physical features of emerging vortex beams are studied when they propagate in free space. The Rayleigh-Sommerfeld vector theory is used to study propagation of the vortex laser beams in different diffraction zones excited by the modes of a dielectric waveguide quasi-optical resonator upon incidence on a spiral phase plate. It is shown that the interaction of a spiral phase plate with a linearly polarized EH₁₁ mode forms a ring (n = 1, 2) due to field structure with an intensity maximum at the center (n = 0). For the azimuthally polarized TE₀₁ mode, the ring (n = 0) field structure transforms into a field distribution with an intensity maximum at the center (n = 1) and then back to a ring (n = 2). In this case, the phase front of the EH₁₁ mode beam turns from a spherical shape to a spiral one with one singularity point on the axis, while a region with two singularity points appears off the axis for the phase structure of the TE₀₁ mode beam.