Sharp and moderate focusing of the combined modes of a terahertz laser
Abstract
Background: The problem of sharp and moderate focusing of combined modes of a dielectric waveguide laser is considered. The results of research on different types of focusing of laser beams have a wide range of potential applications, from imaging and spectroscopy to communication, sensing, biomedicine and solving problems related to the interaction of electromagnetic waves with matter: diagnostics of thin films, surfaces of materials, of various biological objects and achieving subwavelength resolution of THz tomography.
The aim of the work is to establish the physical behavior of sharp and moderate focusing of laser radiation beams described by combined linearly polarized modes of a circular hollow dielectric waveguide.
Materials and methods: The vector theory of Rayleigh-Sommerfeld was used to study the focusing of laser beams excited by the modes of a quasi-optical waveguide resonator. Well-known methods of measuring the spatial-energy characteristics of laser beams in the THz range for experimentally study of these phenomena were used.
Results: The physical features of the spatial-energy characteristics of laser radiation beams with linear field polarization at sharp and moderate focusing in free space have been established theoretically and experimentally.
Conclusion: It is shown that the total field intensity of both combined TE0n+EH2n and EН-1n+EH3n-мод
(n = 1, 2, 3) is defined by all three components and has a dip on the axis for both types of focusing. The central maxima of the field of these modes are significantly shifted from the geometric foci of the investigated lenses as the order n of these modes increases. The EН-11+EH31-mode has the smallest diameter of the focal spot in the region of maximum intensity with sharp focusing, the TE03+EH23-mode has the largest diameter of the focal spot with moderate focusing.
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References
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