基于强激光辐照固体锡靶产生极紫外光源的实验研究

建立了一套利用高功率YAG激光器辐照固体锡靶产生高转换效率极紫外光 (extreme ultraviolet) 源的实验装置.利用建立的实验装置开展了极紫外光源的强度和转换效率与抽运激光强度关系的实验研究,发现极紫外光源的转换效率随抽运激光强度的变化具有饱和效应.实验发现：当抽运激光能量达到250mJ时,极紫外光源的转换效率最高,波长为13.5nm处0.27nm带宽范围内的极紫外光源的能量转换效率为1.6%,此时对应的激光强度为1.8×10¹¹W/cm². 关键词： 极紫外光 转换效率     

A closer look into DESIRE for NMR microscopy

The major challenge of nuclear magnetic resonance (NMR) microscopy at a spatial resolution of a few micrometers is to obtain a sufficiently high signal-to-noise-ratio (SNR) within a reasonable measurement time. As a particular difficulty, molecular self-diffusion poses a serious limitation to true spatial resolution and SNR if conventional Fourier encoding techniques are used. Opposed to that, the alternative DESIRE (Diffusion Enhancement of SIgnal and REsolution) approach to NMR microscopy utilises diffusion to increase the SNR. Being a real-space imaging method, spatial localisation is accomplished by saturation pulses while diffusion continuously replaces the saturated by unsaturated spins. For this technique a signal enhancement of up to three orders of magnitude has been predicted and initial experimental data have provided a proof of principle. In the present work, a detailed investigation of one-dimensional (1D) DESIRE is presented including simulations of a real implementation of the method, a quantitative experimental analysis, and basic 1D imaging. The simulations reveal the importance and provide the means of ensuring the true spatial resolution for this particular way of localisation, enable the selection of useful experimental parameters, and predict the specific image contrast to be expected around barriers restricting diffusion. Experimental data are presented with resolutions down to 3 microm and DESIRE enhancement up to 25 that are in good agreement with the simulation results. In particular, 1D DESIRE imaging in a phantom confirms the expected signal drop close to barriers due to spatially restricted diffusion.     

Birkhoff系统约化的Routh方法

研究Birkhoff系统的约化.首先,列出系统的运动微分方程及其循环积分;其次,构造Birkhoff系统的Routh函数组,利用循环积分约化Birkhoff系统的运动微分方程,并使约化后的动力学方程仍保持Birkhoff方程的形式;最后,举例说明结果的应用. 关键词： Birkhoff系统 约化 循环积分     

Single-transverse-mode output from a fiber laser based on multimode interference

An alternative original approach to achieve single-transverse-mode laser emissions from multimode (MM) active fibers is demonstrated. The fiber cavity is constructed by simply splicing a conventional passive single-mode fiber (SMF-28) onto a few centimeters-long active MM fiber section whose length is precisely controlled. Owing to the self-imaging property of multimode interference (MMI) in the MM fiber, diffraction-limited laser output is obtained from the end of the SMF-28, and the MMI fiber laser is nearly as efficient as the corresponding MM fiber laser. Moreover, because of the spectral filtering effect during in-phase MMI, the bandwidth of the MMI fiber laser is below 0.5 nm.     

Properties of Strain Compensated Symmetrical Triangular Quantum Wells Composed of InGaAs/InAs Chirped Superlattice Grown Using Gas Source Molecular Beam Epitaxy

We investigate the properties of symmetrical triangular quantum wells composed of InGaAs/InAs chirped superlattice, which is grown by gas source molecular beam epitaxy via digital alloy method. In the quantum well structure tensile AlInGaAs are used as barriers to partially compensate for the significant compressive strain in the wells, the strain compensation effects are confirmed by x-ray measurement. The photoluminescence spectra of the sample are dominated by the excitonic recombination peak in the whole temperature range. The thermal quenching, peak energy shift and line-width broadening of the PL spectra are analysed in detail, the mechanisms are discussed.     

Multiferroic behaviour of epitaxial NiFe2O4--BaTiO3 heterostructures

Multiferroic NiFe2O4 （NFO）-BaTiO3 （BTO） bilayered thin films are epitaxially grown on （001） Nb-doped SrTiO3 （STO） substrates by pulsed-laser deposition （PLD）. Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with （001）-orientation, i.e. （001）-NFO/（001）-BTO/substrate and （001）- BTO/（001）-NFO/substrate. Microstructure studies from x-ray diffraction （XRD） and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious magnetoelectric （ME） effect on coupling response.     

铁基纳米晶合金的介观阻抗率及应用

提出了铁基纳米晶合金介观阻抗率的物理概念，用Maxwell方程组求得其计算公式ρ=-μ{A}/{t}/Δ×H，该式表明铁基纳米晶合金的介观阻抗率与材料内部的介观磁场强度H、介观磁矢势A和介观磁导率μ有关，磁矢势A是由介观结构引起的量子力学效应，是由合金的微观结构决定的.这个理论很好地解释了铁基纳米晶粉末、粉芯     

Versatile Nitro-Fluorophore as Highly Effective Sensor for Hypoxic Tumor Cells: Design, Imaging and Evaluation

Based on the characteristics of a nitro-group, which can be partially or totally reduced to an amino-group in hypoxic cells, two series of hypoxic sensors containing 7H-Benzimidazole [2,1-a]benz[de]isoquinolin-7-one cores with nitro groups in different positions were designed, synthesized and evaluated. The target compounds exhibited significantly different fluorescence characteristics (fluorescence enhancement or quenching). The strong fluorescences of some partially reduced compounds could be explained through the examination of their infrared spectra, which showed a restriction of the nitro-group vibration. These compounds exhibited significant hypoxic–oxic fluorescence differences not only in numerical values but also in their fluorescent imaging properties as reported for the first time.      

Possible implications of the channeling effect in NaI(Tl) crystals

The channeling effect of low energy ions along the crystallographic axes and planes of NaI(Tl) crystals is discussed in the framework of corollary investigations on WIMP dark matter candidates. In fact, the modeling of this existing effect implies a more complex evaluation of the luminosity yield for low energy recoiling Na and I ions. In the present paper related phenomenological arguments are developed and possible implications are discussed at some extent. PACS 95.35.+d     

Finite element modeling of laser-induced three-dimensional Transient Thermal Grating in two-layered systems

The three-dimensional (3D) temperature field of laser-induced transient thermal grating (TTG) for two-layered structures such as diamond/substrate is obtained by the finite element method (FEM). The numerical results indicate that the thickness of the diamond film has a significant influence on the temperature field. On the other hand, we further find that variation of the substrate significantly affects on the temperature distribution in the diamond film, which has been ascribed to the various thermal conductivities of the substrates.