TiO2∶Mo体系的光子雪崩上转换

在 978nm激光二极管的激发下 ,Mo掺杂的TiO2 材料表现出很强的宽带上转换发光 ,该发光来源于 [MoO4]2 - 基团的激发态3T1 ,3T2 能级到基态1 A1 能级的电子跃迁 .通过研究发光强度与抽运功率的关系及上转换发光的上升时间曲线 ,发现TiO2 ∶Mo体系的上转换发光中存在着雪崩机制 ,应用转换函数理论分析了光子雪崩的产生条件和主要特征 ,理论结果和实验数据很好地符合     

X-ray damage characterization in BaLiF3,KMgF3 and LiCaAlF6 complex fluorides

Two-inch sized KMgF₃,BaLiF₃ and LiCaAlF₆ (LiCAF) single crystals were grown by the Czochralski method under a CF₄ atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the ultra-violet and visible spectral regions. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials. It is found that the amplitude of the F-absorption band is suppressed more than a factor of 3 by Mg-doping. For Mg-doped crystals, the optimum doping concentration is about 0.2 mol% of Mg²⁺.     

Anomalies in the Absorption and Reflection of a High-Power Ultrashort Laser Pulse by a Plasma with a Solid-State Density

The patterns of absorption and reflection of an ultrashort laser pulse by a plasma with a solid-state density, which are realized in the mode of the normal skin effect, are studied. It is shown that a decrease in low-power pulse duration shorter than the period corresponding to the fundamental frequency of radiation leads to an increase in the absorption coefficient. If the pulse power is so high as to provide electron heating during a time shorter than the reciprocal fundamental frequency, nonlinear suppression of absorption takes place and the spectrum of the reflected radiation contains odd harmonics of the fundamental frequency.     

Determination of optical nonlinearities in Cu(mpo)2 by Z-scan technique

The optical nonlinearities of Cu(mpo)₂ [formula = C₁₀H₈N₂CuO₂S₂] complex have firstly been investigated by using the Z-scan technique with a nanosecond-pulsed Nd:YAG laser at its second harmonic (532 nm) radiation. The nonlinear optical absorption and refraction coefficients of Cu(mpo)₂ have been measured with the different on-axial peak irradiances I ₀ at the waist ranging from 0.48 to 5.66 GW/cm². The nonlinear transmittance characteristics exhibit the near resonant two-photon absorption (TPA) at 532 nm and are explained by a population redistribution model. The nonlinear absorption originates from the near resonant TPA while the mechanism of the nonlinear refraction is the near resonant TPA transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant TPA.     

Quantum Nonlocality of Photon Pairs in Interference in a Mach-Zehnder Interferometer

Nonlocal character of entangled photon pairs generated in spontaneous parametric downconversion is demonstrated. One photon from a pair propagates through a Mach-Zehnder interferometer and is detected in coincidence-count measurement with its twin. Width of the coincidence-count interference pattern (measured for various values of path difference in the Mach-Zehnder interferometer) depends on spectral width of the twin as a result of entanglement of photons in a pair. The experimental setup is analyzed for a Gaussian spectral filter and a Fabry-Perot resonator. It is shown that nonlocal interference is much stronger for cw pumping in comparison with femtosecond pulsed pumping for values of parameters commonly used in spontaneous parametric downconversion experiments.     

Failure of the Quasiparticle Picture of X-ray Absorption?

The Golden rule expression for x-ray absorption spectra (XAS) is typically calculated within a one-particle (quasiparticle) approximation and generally leads to good agreement between theory and experiment. The fact that a quasiparticle approximation works fairly well is surprising, since it neglects satellite excitations and intrinsic losses due to a suddenly created core-hole. The resolution of this paradox requires physics beyond the independent particle approximation. This is discussed here using an effective Green's function formulation based on a quasi-boson model that takes interference between inelastic losses into account. This approach shows that inelastic excitations such as multi-electron excitations tend to be suppressed, and that the XAS is given by a broadened quasiparticle particle approximation, together with weak satellite structure and edge singularity effects.     

Two-function upward-downward minimax theorems

Two-function upward-downward minimax theorems are derived which contain Simons upward-downward minimax theorem as well as Domokos minimax theorem as special cases. Here the convexity assumptions on two functions are given by mixing up their values as means proposed by Lin and Quan.     

Structure and optical properties of lead iodide based two-dimensional perovskite compounds containing fluorophenethylamines

Phenethylammonium-based perovskites, which can be regarded as a semiconductor/insulator multiple quantum well consisting of lead halide semiconductor layers sandwiched between phenethylammonium insulator layers were prepared. To investigate the effects of the electronic state and the orientation of organic insulator layers on the optical properties of layered perovskites, fluorine substituted analogues were also prepared. The structure and optical properties were investigated by the XRD, UV–Vis absorption, and fluorescence measurements. The exciton absorption peak was shifted by the substitution of fluorine atoms in organic ammonium compounds. It became clear that the optical properties of two-dimensional perovskite compounds were controlled by the substitution of fluorine atoms.     

用光学差分吸收光谱监测大气中污染气体浓度

在实验室内模拟测量了实际大气中污染气体的差分吸收光谱 (DOAS) .本文在介绍差分吸收光谱技术同时 ,分析计算了污染气体的浓度 .实验设计中被测气体为大气中的 2种主要污染气体 :工业锅炉的主要排放物SO2 和机动车尾气的主要成分NO .用氘灯作为光源测量其在紫外波段的特征吸收 ,并通过光纤束连接光栅光谱仪 ,由计算机自动采集和处理数据 .     

Binding of erbium(III) and holmium(III) to native and chemically modified alfalfa biomass: a spectroscopic investigation

Traditional treatment methods used to clean-up heavy metal contamination of soils and waters are cost intensive whereas more cost effective methods need to be developed. The use of plant materials to remediate heavy contamination has been studied for the past two decades. This technique has shown much promise for many of the common heavy metal contaminants, but few studies have focused on the lanthanide series elements. By investigating the binding and interactions of the lanthanide elements to alfalfa biomass, a more complete understanding of the binding mechanisms and the interactions of heavy metals with biomaterials can be obtained. Different chemical functional groups on the alfalfa biomass, carboxyl, amino, sulfur, and ester groups, were modified to investigate the binding mechanisms of erbium(III) and holmium(III). Batch experiments were performed with native and chemically modified alfalfa biomass suggesting that the carboxyl groups play a major role in the binding of erbium(III) and holmium(III) to the alfalfa biomass. In addition, X-ray absorption spectroscopy (XAS) studies corroborated the data obtained from the batch experiments.