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

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.