Mr. Ji Qi Profile

Ji Qi

at Capital Normal Univ

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Proceedings Article | 9 September 2021 Paper

Influence of dielectric environment on the resonant characteristics in anisotropic terahertz metamaterials

Hongru Ma, Chenxin Ding, Ji Qi, Zhengyan Liu, Pujing Zhang, Qingli Zhou, Cunlin Zhang

Proceedings Volume 11909, 119090V (2021) https://doi.org/10.1117/12.2605591

KEYWORDS: Terahertz radiation, Dielectrics, Absorption, Refractive index, Dielectric polarization, Transmittance, Terahertz metamaterials, Metamaterials, Electromagnetism, Statistical analysis

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Highly sensitive response of anisotropic terahertz metamaterials to electromagnetic waves has attracted considerable attention due to its potential applications in terahertz modulators and biosensing devices. We designed three microstructure samples with split ring arrays. The terahertz transmission spectra are experimentally measured at different rotation angle. It is found that as the rotation angle increases, the resonance mode has gradually evolved from a single dipole oscillation mode to the double oscillation modes accompanied with LC and dipole oscillations, we further simulated the polarization conversion characteristics of the single splitting rings. It shows that the highest conversion efficiency appears at 45 degrees. But it doesn’t have polarization conversion effect at 0° and 90°. Subsequently, we have utilized ultrashort pulse laser to optically control the electromagnetic response by exciting the photogenerated carriers in the metamaterial samples. The experimental data show that the transmittance change obviously with the pump light. Additionally, when the angle is 90 degrees, it can be observed that the LC resonance annihilates earlier than the resonance of the dipole resonance with the increase of pump power, implying the former is particularly sensitive to the variation of the dielectric environment. To further explore the influence of dielectric environment on the resonance characteristics of the terahertz metamaterials, we have further performed the simulations with the applied surface analyte of different refractive index. The simulated data show that with the increase of the refractive index of the surface analyte, the resonance frequency of the dipole oscillation has a more significant blue shift than the resonance frequency of the LC oscillation. Our obtained results could provide the idea for designing terahertz modulators and sensitive biosensing devices.

Proceedings Article | 9 September 2021 Paper

Active control properties and coupling effect in the terahertz metamaterials

Ji Qi, Zhengyan Liu, Hongru Ma, Chenxin Ding, Pujing Zhang, Qingli Zhou, Cunlin Zhang

Proceedings Volume 11909, 119090R (2021) https://doi.org/10.1117/12.2605546

KEYWORDS: Terahertz radiation, Oscillators, Absorption, Terahertz metamaterials, Dielectrics, Metamaterials, Electromagnetism, Split ring resonators, Modulation, Control systems

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We modulate the electromagnetic response of terahertz metamaterials by exciting photogenerated carriers with ultra-short pulsed laser, and realize the active control of terahertz transmission and resonances in a wide band. The experimental results show that when the terahertz electric vector is perpendicular and parallel to the bar direction with the open gap in the circular split ring resonators, respectively, the transmission of the non-resonant region and resonance absorption are significantly tuned by the irradiated pump pulse. With the increase of the pump power, the resonance absorption peak decreases and the frequency of resonance dip has a remarkable blue-shift. Meanwhile, the transmission of the non-resonant region decreases correspondingly. It is also found that the blue-shift of the resonance is mainly determined by the change of conductivity and dielectric constant in the photoexcited layer of the substrate. Through the numerical simulation, we have further proved the introduction of pump light has a significant modulation effect on the electromagnetic properties of terahertz metamaterials. Additionally, it can be observed that the LC resonance annihilates earlier than the resonance of the dipole resonance with the increase of pump power, implying the former is particularly sensitive to the variation of the active control. In the theoretical analysis, based on the Lorenz oscillator model, we have derived and calculated the resonance response intensity of the coupled oscillators under an external field. The calculated results indicate the coupling coefficient and damping rate have an impact on the spectra evolution, showing that the resonant response peak has a remarkable blue-shift with the increase of coupling coefficient and the resonance response intensity decreases with the increase of damping rate.

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