Focusing of Modes for Metallic Resonator of a Terahertz Laser with Nonuniform Spatial Polarization

Theoretically, based on the Rayleigh-Sommerfeld vector theory using the radiation of a waveguide terahertz laser (λ = 432.6 μm), physical features of moderate and sharp focusing of radiation beams were studied. Laser beams are excited by the modes of a laser cavity based on a circular metal waveguide for inhomogeneous spatial polarization of the field. It is shown that in the focal region of the lens, in the case of a moderate and sharp focusing of the radiation beam excited by the TM11 mode with a nonuniform polarization, a minimum of its axial intensity is observed. It is due to the significant influence in this case of the intensity of the longitudinal component of the field of the given mode. The obtained results expand the knowledge about the features of the focusing for the laser beams of terahertz range.