Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without changing their composition. In this work, we investigate the electronic, optical, and mechanical properties of antiperovskite X₃NP (X²⁺ = Ca, Mg) upon compression by first-principles calculations. Our results reveal that the system is anisotropic, and the lattice constant a of X₃NP exhibits the fastest rate of decrease upon compression among the three directions, which is different from the typical Pnma phase of halide and chalcogenide perovskites. Meanwhile, Ca₃NP has higher compressibility than Mg₃NP due to its small bulk modulus. The electronic and optical properties of Mg₃NP show small fluctuations upon compression, but those of Ca₃NP are more sensitive to pressure due to its higher compressibility and lower unoccupied 3d orbital energy. For example, the band gap, lattice dielectric constant, and exciton binding energy of Ca₃NP decrease rapidly as the pressure increases. In addition, the increase in pressure significantly improves the optical absorption and theoretical conversion efficiency of Ca₃NP. Finally, the mechanical properties of X₃NP are also increased upon compression due to the reduction in bond length, while inducing a brittle-to-ductile transition. Our research provides theoretical guidance and insights for future experimental tuning of the physical properties of antiperovskite semiconductors by pressure.

We present the perfect light absorption of monolayer molybdenum disulfide (MoS2) in a dielectric multilayer system with two different Bragg mirrors. The results show that the strong absorption of visible light in monolayer MoS2 is attributed to the formation of optical Tamm states (OTSs) between two Bragg mirrors. The MoS2 absorption spectrum is dependent on the layer thickness of Bragg mirrors, incident angle of light, and the period numbers of Bragg mirrors. Especially, the nearly perfect light absorption (99.4%) of monolayer MoS2 can be achieved by choosing proper period numbers, which is well analyzed by the temporal coupled-mode theory.

针对固体、液体不同形态易燃易爆危险物品准确识别的要求，设计并搭建了多组件太赫兹时域波谱仪。用该波谱仪检测了两种不同形态的易燃易爆危险品。测试结果表明，该波谱仪在0.1～2 THz频谱范围内检测危险品时都能得到明显的特征吸收峰，因此可以使用该波谱仪识别不同形态的危险品，并为公共安全检查提供一种新的方法。

In this work, it has been demonstrated that in order to fully understand the terahertz (THz) pulse generation process during femtosecond laser filamentation, the interaction between THz wave and air plasma has to be taken into account. This interaction is mainly associated with the spatial confinement of the THz pulse by the plasma column, which could be described by the one-dimensional negative dielectric (1DND) waveguide model. By combining the 1DND model with the conventional four-wave mixing (4WM) and photocurrent (PC) models, the variation of THz spectral amplitude and width obtained in experiments could be better understood. Finally, a three-step procedure, with 1DND bridging 4WM and PC processes, has been established for the first time to describe the underlying mechanism of THz radiation from plasma sources.