RADIO PHYSICS AND RADIO ASTRONOMY

Purpose: The purpose of the work is to develop a new method for determining the complex dielectric permeability of dielectrics in mm and submm wavelength ranges.

Design/methodology/approach: The proposed method consists in registration of parameters of a plasmon polariton resonance, which arises at diffraction of electromagnetic radiation on a diffraction grating created on the surface of the conductive medium (metal or semiconductor) and registration of changes in these parameters when applied to the grating film of the material whose dielectric permeability should be found. On the laboratory unit, created on the basis of the terahertz HCN-laser, the dependence of the intensity of radiation, mirrored reflected from the grids, from the angle of incidence and determined the position and width of the plasmon-polaritone resonance for a clean grid and the same grid covered with the dielectric film. From comparison of these parameters, the values of the resonance shear and widening caused by the presence of the film were found. On the other hand, from the theoretical solution of the mentioned problem of diffraction under the conditions of a plasmon-polaritone resonance, the dependences of the resonance shear and width on optical characteristics of the investigated film (under the conditions of its small optical thickness) were found. Comparison of experimentally found and theoretically defined values of displacement and width of the resonance allows to determine the complex dielectric permeability of the film (at its known thickness).

Findings: Test measurements of the complex dielectric permeability of the reference polypropylene film have been made by the proposed method. The measurements have been compared with the known data obtained earlier by spectroscopic and interferometric methods. It was found that the obtained and known values of the actual parts of the polypropylene dielectric permeability differ by less than 10 %, and the values of their imaginary parts coincide in the order of magnitude.

Conclusions: The received results testify to suitability of the offered method for operational express measurements of optical characteristics of dielectrics films with small optical thickness.

Key words: measurement of optical characteristics, dielectric permeability, terahertz range, electromagnetic radiation diffraction, plasmon polariton resonance

Manuscript submitted  22.06.2020

Radio phys. radio astron. 2020, 25(3): 231-239

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