The absorption coefficient of magnesium-doped near-stoichiometric lithium niobate crystal is measured by terahertz time-domain spectroscopy in a frequency range of 0.2 THz^0.9 THz at room temperature. The absorption coefficient is modulated by external optical pump fields. Experimental results show that the absorption coefficient of near-SLN：Mg crystal is approximately in a range of 22 cm- 1_35 cm- 1 in a frequency range of 0.2 THz-0.9 THz and tunable up to nearly 15%. Further theoretical analysis reveals that the variation of absorption coefficient is related to the number of light-induced carriers, domain reversal process, and OH- absorption in this crystal.
We design and analyze a novel multiband left-handed metamaterial based on a fishnet-like structure at terahertz （THz） frequencies.The metamaterial exhibits simultaneous negative refractions around the frequencies of 0.48,1.05,and 1.19 THz for the electromagnetic （EM） wave normal incidence,and around the frequencies of 0.20,0.79,and 1.13 THz for parallel incidence.The simulated results verify the left-handed properties.A particularly important observation is the capability of the proposed metamaterial with a single geometrical structure to display multifrequency operations in a unit cell.The compact metamaterial is a major step toward the miniaturization of THz materials and devices suitable for multifrequencies.
