FREE-SPACE PROPAGATION OF TERAHERTZ LASER VORTEX BEAMS

• Datum: 2024
• Hauptverfasser: Degtyarev, A. V., Dubinin, M. M., Maslov, V. A., Muntean, K. I., Svistunov, O. O.
• Format: Artikel
• Sprache: Ukrainian
• Veröffentlicht: Видавничий дім «Академперіодика» 2024
• Schlagworte: terahertz laser; waveguide resonator; spiral phase plate; vortex beams; polarization; radiation propagation
• Online Zugang: http://rpra-journal.org.ua/index.php/ra/article/view/1442
• Назва журналу: Radio physics and radio astronomy

Subject and Purpose. Currently, numerous ideas and different methods have been in growth for generating vortex beams — areas of the circular motion of the electromagnetic wave energy flow around the so-called phase singularity points caused by a violation of the wave front topological structure. The purpose of this work is to obtain analytical expressions describing the nonparaxial diffraction of wave modes of the waveguide resonator of a terahertz laser during the wave mode interaction with a spiral phase plate. The resulting vortex beams are examined for their physical features in free space propagation.Methods and Methodology. 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.Results. For the first time, analytical expressions have been obtained to describe the nonparaxial diffraction of wave modes of the waveguide resonator of a terahertz laser, when resonator modes interact with a spiral phase plate at different topological charges, n. The physical features of the resulting vortex beams were studied in their free space propagation. It has been shown that a spiral phase plate modifies the structure of the linearly polarized EH₁₁ mode so that the original (n=0) intensity profile with the maximum energy at the center turns at n=1 and 2 into a ring-like donut shape with an energy hole in the center. The azimuthally polarized TE₀₁ mode has originally (n=0) a ring-shaped intensity. At n=1, this configuration changes to have the maximum intensity in the center. At n=2, it becomes annular again. In the process, the spherical phase front of the beam of the linearly polarized EH₁₁ mode becomes spiral and have one singularity point on the axis, whereas the phase structure of the azimuthally polarized TE₀₁ mode gains a region with two phase singularity points off the axis.Conclusions. The results of the study can effectively facilitate information transfer in high-speed THz communication systems. They can provide a real platform to perform tasks related to tomography, exploring properties of materials, detecting astrophysical sources, which makes them very promising in modern technologies.Keywords: terahertz laser; waveguide resonator; spiral phase plate; vortex beams; polarization; radiation propagationManuscript submitted 11.12.2023Radio phys. radio astron. 2024, 29(2): 127-136REFERENCES1. Headland, D., Monnai, Y., Abbott, D., Christophe, F., and Withawat, W., 2018. Tutorial: Terahertz beamforming, from concepts to realizations. APL. Photonics, 3(5), pp. 051101. 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