A reflection-type electromagnetically induced transparency（EIT） metamaterial is proposed, which is composed of a dielectric spacer sandwiched with metallic patterns and metallic plane. Experimental results of THz time domain spectrum（THz-TDS） exhibit a typical reflection of EIT at 0.865 THz, which are in excellent agreement with the full-wave simulations. A multi-reflection theory is adopted to analyze the physical mechanism of the reflection-type EIT, showing that the reflection-type EIT is a superposition of multiple reflection of the transmission EIT. Such a reflection-type EIT provides many applications based on the EIT effect, such as slow light devices and nonlinear elements.
Tuning the dielectric permittivity spectra of strontium titanate （SrTiO3） single crystals in an extemal optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. The application of the optical field leads to an appreciable tuning of the permittivity, reaching up to 2.8%, with the dielectric loss changing about 3%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of the refractive index responds linearly to the applied light power. These findings are attributed to a linear electro-optical effect of the internal space charge field of the crystal.
A kind of functional graphene thin film metamaterial on a metal-plane separated by a thick dielectric layer is designed for terahertz(THz) absorbers.We investigate the properties of the graphene metamaterial with different interlayers in the 0–3 THz range.The simulation results show that the absorption rate reaches up to 99.9% at the frequency of 1.917 THz.Changing the period to 80 μm×18 μm can get a narrow-band high quality factor(Q) absorber.We present a novel theoretical interpretation based on the standing wave field theory,which shows that the coherent superposition of incident and reflection rays produces standing waves,and the field energy is localized inside the thick spacers and dissipates through the metal-planes.
