Spatial-energy field characteristics for symmetric modes of metallic waveguide resonator of terahertz laser

Theoretical and experimental comparison of the divergence of TE01 mode and Gaussian beam can be concluded that the obtained analytical expressions in nonparaxial approximation correctly describe the propagation of waveguide modes in free space. Stable structure of the field for the symmetric waveguide modes in the terahertz range is observed at shorter distances, unlike the distances predicted by the well-known Rayleigh criterion for the far-field diffraction.