Tight focusing of terahertz vortex beams formed by laser dielectric resonator

Wave characteristics of vortex laser beams during their tight focusing have been theoretically studied. The Rayleigh–Sommerfeld theory was used to describe propagation in free space of laser beams excited by the modes of a waveguide dielectric resonator. It is shown that at the topological charge of the spiral phase plate n = 0, the studied EH11 mode has a maximum of radiation intensity on the axis. Introduction of a topological charge leads to the appearance of a minimum of radiation intensity on the axis as well as to the increase in the size of the focal spot. However, for the TE01 mode with the topological charges n = 0 and n = 2, the intensity distribution retains a ring shape, while at n = 1 the beam profile turns into the Gaussian-like one. The wave front in the focal region of the lens for the components of the EH11 and TE01 modes transforms from spherical to spiral one with increasing the topological charge.