Wang Kejia

Dual-Band Terahertz Left-Handed Metamaterial with Fishnet Structure

We present the design of a dual-band left-handed metamaterial with fishnet structure in the terahertz regime. Its left-handed properties are described by the retrieved effective electromagnetic parameters. We introduce an equivalent circuit which offers a theoretical explanation for the left-handed behavior of the dual-band fishnet metamaterial, and investigate its losses receiving higher figure of merit. The design is beneficial to the development of frequency agile and broadband THz materials and devices. The dual-band fishnet metamaterial can be extended to infrared and optical frequency ranges by regulating the structural parameters.

Effects of a one-dimensional surface defect on designer surface plasmon polaritons

By using a finite difference time domain (FDTD) method, the effects of a one-dimensional (1D) surface defect on designer surface plasmon polaritons (designer SPPs) supported by a 1D metallic grating in THz domain are investigated. When the size of the defect is in a special range which is not too large, the designer SPPs reflected and scattered by the defect are weak enough to be neglected. The defect only induces a disturbance in the energy distribution of the designer SPP supported by the whole defect grating. If the defect size exceeds the said range, the reflecting and scattering are dominant in the influences of the defect on designer SPPs. Our analysis opens opportunities to control and direct designer SPPs by introducing a 1D defect, especially in low frequency domain.

Morphology Dependence of Power Spectra for Different Polarized States from Two-Dimensional Active Random Media

Spectra for two polarized states with competition on the inverted population in a set of two-dimensional (2D) active random media are calculated, and these random media have the same random constitution but different shapes. Results show that the power spectra for the two polarized states are all morphology dependent in the competition. The appropriate design of the shapes has an obvious effect on the selection of TM polarized modes and can improve the adverse situation of the TM polarized state in the competition. Such a property presents a new mode-selecting technique for each polarized mode in random media.

Excitation of localized modes and mechanism of random lasing forming in random media

Laser phenomena in random media have been studied based on the localized theory for lightwave in random media. The relationship between random lasing modes and localized modes has been investigated by directly solving Maxwell equations numerically via the finite difference time domain method. The spatial distribution and the spectra of localized modes are obtained for both passive and active random media. The results show that random lasing modes directly originate from the localized modes inside the random medium. In the presence of gain, any one of the localized modes can be amplified and can serve as random lasing mode.

Theoretical investigation on generating terahertz radiation from gas plasma induced by three-color ultrashort lasers*

Generation of intense broadband terahertz (THz) waves from gas plasma induced by tri-color ultrashort (fundamental (ω), second harmonic (2ω), and third harmonic (3ω)) laser pulses is theoretically investigated. Simulation results show that the 3ω laser pulse can greatly enhance or suppress the generation of THz wave at different values of relative phase (θ 3) between the 3ω and ω fields. Moreover, the polarities of the generated THz waves can be controlled by changing θ 3, with the relative phase θ 2 (between the 2ω and ω fields) fixed to be a certain value. All of our results show that θ 3 plays a key role in the generation process, which promises to control the intensity as well as the polarity of gas plasma-induced THz radiation.