非晶态Si/SiN_x超晶格材料的发光与非线性光学特性

采用射频磁控反应溅射技术制备了a-Si/SiN_x超晶格材料,并采用热退火技术对材料进行处理。利用吸收光谱和X射线衍射谱对材料进行表征,结果表明Si层呈现非晶态。为研究材料的三阶非线性光学特性,对材料进行Z扫描研究,测量数据表明,材料的非线性吸收为反饱和吸收,材料非线性折射率呈现为负值,该材料的χ(3)的实部为4.57×10~(-17)C(1.39×10~(-7)esu),虚部为1.49×10~(-17)C(4.48×10~(-8)esu),该极化率数值比体硅材料的χ(3)值大5个数量级。对该材料非线性光学产生的机理进行了研究,认为材料体现出的较强的量子限制效应是非线性极化率增强的主要来源。     

Proof of factorization using background field method of QCD

Factorization theorem plays the central role at high energy colliders to study standard model and beyond standard model physics. The proof of factorization theorem is given by Collins, Soper and Sterman to all orders in perturbation theory by using diagrammatic approach. One might wonder if one can obtain the proof of factorization theorem through symmetry considerations at the lagrangian level. In this paper we provide such a proof.     

Radiation damage in soft X-ray microscopy

The rates of chemical transformation by radiation damage of polystyrene (PS), poly(methyl methacrylate) (PMMA), and fibrinogen (Fg) in a X-ray photoemission electron microscope (X-PEEM) and in a scanning transmission X-ray microscope (STXM) have been measured quantitatively using synchrotron radiation. As part of the method of dose evaluation in X-PEEM, the characteristic (1/e) sampling depth of X-PEEM for polystyrene in the C 1s region was measured to be 4 ± 1 nm. Critical doses for chemical change as monitored by changes in the X-ray absorption spectra are 80 (12), 280 (40) and 1230 (180) MGy (1 MGy = 6.242*ρ eV/nm³, where ρ is the polymer density in g/cm³) at 300 eV photon energy for PMMA, Fg and PS, respectively. The critical dose for each material is comparable in X-PEEM and STXM and the values cited are thus the mean of the values determined by X-PEEM and STXM. C 1s, N 1s and O 1s spectroscopy of the damaged materials is used to gain insight into the chemical changes that soft X-rays induce in these materials.     

Flattened chromatic dispersion in square photonic crystal fibers with low confinement losses

This research presents a simple index-guiding square photonic crystal fibers (SPCFs) that has a silica core surrounded by air hole with two different diameters. It is demonstrated that the designed two-different-size hole-arrayed index-guiding SPCFs has a ultra-flattened chromatic dispersion of 0 ± 0.9 ps/(nm·km) in a wavelength range of 1.34 to 1.61 μm and low confinement loss of less than 10⁻⁷ dB/m in a wavelength range of 1.2 to 1.7 μm. It has also been shown that the proposed SPCFs show reasonable dispersion tolerance.     

Correlation of soft magnetic properties with free volume and medium range ordering in metallic glasses probed by fluctuation microscopy and positron annihilation technique

Amorphous ribbons of different thicknesses of Co_64.5Fe_3.5Si₁₆B₁₄Ni₂ alloy were synthesized using the melt spinning technique by varying wheel speed. The effect of cooling rate on the ribbon thickness and their soft magnetic properties have been studied. The amorphous structure has been characterized in terms of structural free volume and medium range order (MRO) by positron annihilation spectroscopy and fluctuation electron microscopy techniques. Positron lifetime spectra of amorphous samples showed two lifetime components. The first component was found to be correlated with MRO whereas, the second lifetime component was found to be associated with nanovoid type of defects, and the second component was strongly dependent on processing conditions. It could be established that the coercivity of the amorphous samples produced by the rapid solidification technique mainly depends on the defects formed during processing rather than change induced in MRO.     

Strongly confined semiconductor quantum dots: Pair excitations and optical properties

This paper reviews a microscopic model of basic electron-hole pair excitation processes in strongly confined semiconductor quantum dots (QD) and their influence on the optical QD properties. The effects of valence band mixing, Coulomb interaction, and surface polarization are taken into account. The exciton and biexciton wave functions and energies are obtained using a numerical diagonalization method. The computed optical spectra, such as absorption, gain, pump-probe, and two-photon absorption, agree well with experiments.     

软X射线监测系统的建立与国际标准的比对

软Ｘ射线监测系统的建立，结构特点和性能，有效地解决了气体的吸收和窗膜的透过率等因素的影响。申请获得了美国布鲁克海文国家实验室（ＢＮＬ）的用光时间，对监测系统的性能进行研究，并给出了该系统的精度及与国际标准的比对结果。     

Dynamical chiral-symmetry breaking at T = 0 and T ≠ 0 in the Schwinger-Dyson equation with lattice QCD data

Dynamical chiral-symmetry breaking (DCSB) in QCD is investigated in the Schwinger-Dyson (SD) formalism based on lattice QCD data. From the quenched lattice data for the quark propagator in the Landau gauge, we extract the SD integral kernel function, the product of the quark-gluon vertex and the polarization factor in the gluon propagator, in an Ansatz-independent manner. We find that the SD kernel function exhibits the characteristic behavior of nonperturbative physics, such as infrared vanishing and strong enhancement at the intermediate-energy region around p 0.6GeV. The infrared and intermediate energy region (0.4GeV < p < 1.5GeV) is found to be most relevant for DCSB from analysis on the relation between the SD kernel and the quark mass function. We apply the lattice-QCD-based SD equation to thermal QCD, and calculate the quark mass function at the finite temperature. Spontaneously broken chiral symmetry is found to be restored at high temperature above 110 MeV.