| Abstract [eng] |
Terahertz (THz) frequency electromagnetic radiation, which occupies the spectrum between infrared and microwave radiation, is receiving considerable attention in scientific and industrial areas due to its unique properties of this radiation. The low photon energy of terahertz radiation results in high transmittance in materials that are opaque to the optical range, which, in turn, determines the potential for this radiation to be used in metrological and imaging applications. Along with the spread of radiation applications in the THz region, there is an increase in demand for optical elements such as polarizers for the THz range. For these reasons, the challenge of developing and manufacturing optical elements suitable for THz frequency radiation is currently very relevant from both a commercial and scientific point of view. The aim of this work was to produce a polarization structure operating in a wide terahertz frequency range (0.5-3 THz) with high extinction contrast value. This paper presents the results of the RCWA (Rigorous Coupled Wave Analysis) method for the theoretical characterization of a metal lattice polarizing element, the analysis of structure fabrication using a direct laser ablation system, and presents experimentally measured dependence of the polarizer extinction contrast values in the investigated THz frequency range. Dependences of the characteristics of the polarization structure on its main geometrical parameters (fill factor, period and metal layer thickness) in the 0.5–3 THz spectral range are demonstrated and the dependences of the element reflection, transmittance and extinction contrast values on the radiation frequency are presented, in the case of grid period value being 2 μm, layer thickness - 20 nm and fill factor- 0.5. The paper presents a theoretical characterization of the laser optical system used in the metal lattice formation process. Results of numerical calculations and experimental analysis of physical binary phase element generating a near super-Gaussian intensity distribution in the focal plane are demonstrated. Using a theoretically evaluated laser optical system, a two-layer polarization structure of an Ag metal lattice on a Si substrate with an active area of 225 mm^2 was fabricated. Due to the use of two-beam interference, together with presented geometrical phase element, formation of 19 metal lattice lines in one laser scanning line was achieved. Application of this process resulted in a production rate of 5.3 s/mm^2. Furthermore, it was experimentally measured that the average value of the extinction contrast of the polarizing element in the spectral range of 0.5–3 THz is equal to 19 dB. |
