Propagation of Terahertz Laser Vortex Beams from a Metal Waveguide Resonator

The purpose of this work is to obtain analytical expressions describing the nonparaxial diffraction of wave modes of the metal waveguide resonator of a terahertz laser during the wave mode interaction with a spiral phase plate. The Rayleigh-Sommerfeld vector theory is adopted to consider the propagation of vortex laser beams generated by wave modes of the quasi-optical waveguide cavity when interacting with a spiral phase plate in different diffraction zones. The resulting vortex beams are examined for their physical features in free space propagation.