太赫兹波段金属线栅的紫外光控特性研究

doi:10.3964/j.issn.1000-0593(2019)07-2040-06

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Abstract In this paper, modulation characteristics of terahertz polarization transmission are studied based on the character of indium oxide nanofilm and metal wire-grid, using sample, indium oxide nanostructure with metal wire-grid as substrate, which is induced by ultraviolet laser. In the experiment, the indium oxide solution dissolved in ethanol is dripped onto the metal wire-grid, and the solution is just soaked in the gap of the metal wire-grid. At the same time, the temperature of the heating table is adjusted to 340 ℃ to thermal annealing on the indium oxide in the metal wire-grid. The results demonstrate that when the longitudinal direction of indium oxide-metal wire-grid is perpendicular to the polarization direction of terahertz electric field, the transmission intensity of the sample to terahertz is obviously attenuated induced by the low-intensity ultraviolet laser. When the UV power density is 7 mW·cm^-2, the modulation depth of terahertz induced by sample with UV laser can reach 71%. When the longitudinal direction of indium oxide-metal wire grid is parallel to the polarization direction of terahertz electric field, the modulation effect of the sample excited by UV laser on terahertz is obviously weakened. When the UV power density is 7 mW·cm^-2, the modulation depth of terahertz induced by sample with UV laser is about 20%. The presence of oxygen vacancies in indium oxide nanofilm makes the material particularly responsive to UV laser. With the absence of UV laser, oxygen molecules in the sample environment are adsorbed to the surface of indium oxide, and the O^2- ion state is generated due to chemical reaction. When the sample is excited by UV laser with photon energy higher than the width of indium oxide band gap, electron hole pairs are excited on the surface of indium oxide, and the holes are bound by the O^2- ion state and defect state on the surface of indium oxide, so as to release electrons into the conduction band and enhance the conductivity of the sample. Terahertz transmission intensity of indium oxide samples has a good correlation with the conductivity of indium oxide in the terahertz frequency range. Using existence of free electrons oscillating on the metal surface, metal wire-grid makes the electric field direction of terahertz polarized wave which parallel to the longitudinal direction of the metal wire-grid excite the electrons oscillation along the metal wire-grid direction. When electrons collide with atoms in a metal lattice, the polarized wave decay with radiating. However, the terahertz polarized wave whose electric field direction is perpendicular to the longitudinal direction of indium oxide-metal wire grid cannot stimulate free electron oscillation due to the limitation of the periodic structure, and it mainly shows transmission characteristics.In combination with the surface defect characteristics of indium oxide, UV laser can be used as an optically controlled polarization switch of indium oxide-metal wire grid structure, and indium oxide-metal wire-grid structure polarizer can be well applied to optically controlled polarization modulation interahertz frequency range.

Key words：Metal wire-grid; Indium oxide; Terahertz time domain spectroscopy; Polarization

Received: 2018-05-24 Accepted: 2018-09-30

ZTFLH:

O433.4

Corresponding Authors: ZHANG Bo, SHEN Jing-ling E-mail: bzhang@cnu.edu.cn; sjl-phy@cnu.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)07-2040-06 OR https://www.gpxygpfx.com/EN/Y2019/V39/I07/2040