CO_2激光光栅式扫描修复熔石英表面缺陷的实验研究与数值模拟

基于熔石英材料对波长为10.6μm的CO2激光具有强吸收作用这一特点,提出采用CO2激光光栅式多次扫描修复熔石英光学元件表面密集分布的划痕和抛光点等缺陷的方法.实验结果表明,在合理的扫描参数下,元件表面的划痕和抛光点等缺陷可被充分地消除.损伤阈值测试结果表明,表面划痕和抛光点等缺陷被完全消除的元件的损伤阈值可回复到或超过基底的损伤阈值.同时结合有限元软件Ansys的模拟结果分析了CO2激光扫描修复及消除元件表面划痕和抛光点等缺陷的过程.本文为消除元件表面划痕和抛光点等缺陷提供了非常有意义的参考.     

γ射线辐照对掺Yb光纤材料性能的影响

采用改进的化学气相沉积法制备掺Yb石英光纤预制棒,以该预制棒制备了尺寸为10/130μm的双包层掺Yb光纤,将这些光纤分成若干组,在不同剂量的60Coγ辐射源下辐照,测试了光纤在辐射前后的吸收谱和激光性能以及光纤预制棒切片辐照后的吸收.实验结果表明:光纤中已存在的色心缺陷(如氧空位(II))和辐照引起的色心缺陷(如E’心、过氧基以及Yb2+离子)等因素的叠加作用可能导致辐照后的光纤在可见光区域的吸收显著增大;与辐照前相比,辐照后光纤的斜率效率、光-光效率显著下降,剂量越大激光性能下降得越厉害;基于Power-Law定理拟合了光纤辐致损耗与所受剂量的关系曲线,定量分析了不同剂量辐照后光纤激光性能下降的原因.研究结果将为进一步发展抗辐照光纤提供理论和实验依据.     

板条Nd:YAG晶体的合成盘抛光技术

针对高功率板条激光器核心工作器件——板条Nd:YAG晶体的超精密加工开展研究,分析了具有特殊构型的板条Nd:YAG晶体元件的加工性能及工艺难点,提出了一种新的基于合成盘抛光的板条Nd:YAG晶体加工工艺,并对规格为100mm×30mm×3mm的板条Nd:YAG晶体进行了加工实验。实验结果表明,合成盘抛光可以很好地控制元件的塌边现象;通过磨料的优化选择,在合成盘抛光工艺中匹配合适粒度的Al2O3磨料能够实现元件的低缺陷加工,元件下盘后的全反射面平面度达0.217λ(1λ=632.8nm),端面平面度达到0.06λ,表面粗糙度达0.55nm(RMS),端面楔角精度可达2″。     

Helicity-dependent time delays in multiphoton ionization by two-color circularly polarized laser fields

By numerically solving the three-dimensional time-dependent Schrödinger equation, we have invest-tigated multiphoton ionization of hydrogen atom in the two-color circularly polarized (TCCP) laser fields consisting of a strong 400 nm and a much weaker 800 nm pulses. Due to the presence of perturb-bative 800 nm laser pulse, sideband peaks emerge between the above-threshold ionization rings in the photoelectron momentum distributions. Our numerical results show that the sideband peaks exhibit one-lobe structure in the co-rotating TCCP laser fields, while it displays the three-lobe structure in the counter-rotating TCCP laser fields. Moreover, the photoelectron yield of sidebands in the co-rotating TCCP fields is much higher than those of the counter-rotating TCCP fields. These phenomena could be well explained from the perspective of the photon-absorption channels via the selection rules. In-terestingly, an obvious phase shift between the sidebands of different orders from the co-rotating and counter-rotating TCCP fields is observed. This shift indicates the helicity-dependent time delay in the one-photon continuum-continuum transition process.     

On the local nature of the strain field calculation method for measuring heterogeneous deformation of cellular materials

A strain field calculation method based on the optimal local deformation gradient technique has been developed to calculate the ‘local’ strain tensor of cellular materials using cell-based finite element models. The local nature and accuracy of this method may be strongly dependent on the cut-off radius, which is introduced to collect the effective nodes for determining the optimal local deformation gradient of a node. Two different schemes are first analyzed to determine the suitable cut-off radius by characterizing the heterogeneous deformation of Voronoi honeycombs under uniaxial compression and we suggest that in Scheme 1, the cut-off radius defined based on the reference configuration is about 1.5 times the average cell radius; in Scheme 2, the cut-off radius defined based on the current configuration is about 0.5 times the average cell radius. Then, Scheme 3, a combined scheme of the two former schemes, is further suggested. It is demonstrated that the optimal cut-off radius in Scheme 3 characterizes the local strain reasonable well whether the compression rate is low or high. Finally, the strain field calculation method with the optimal cut-off radius is applied to reveal the evolution of the heterogeneous deformation of two different configurations of double-layer cellular cladding under a linear decaying blast load. The 2D fields and the 1D distributions of local engineering strain are calculated. These results interpret the shock wave propagation mechanisms in both claddings and provide useful understanding in the design of a double-layer cellular cladding.     

Effect of thermal treatment on structural change of anode electrocatalysts for direct methanol fuel cells

Commercially available carbon-supported Pt,PtCo and PtRu catalysts from E-TEK are heat-treated in turn at 600 ℃ and 800 ℃ each for an hour.The as-received and as-heated catalysts are used as anode catalysts for direct methanol fuel cells.Structural and surface composition changes induced by heating are analyzed by X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS),respectively.For the Pt catalyst,heating the catalysts caused only the mass activity decrease due to particle sintering,whereas the specific activity and CO tolerance remained unchanged.The performance of the PtCo and PtRu catalysts is affected differently by heating.Heating the PtRu catalyst adversely affects its catalytic activity and its CO tolerance due to Pt depletion at the surface.In contrast,although Pt depletion also takes place for the heated PtCo catalysts,these catalysts show an even higher specific activity and approximately the same CO tolerance.The observed difference is likely due to the optimum atomic ratio difference for Ru/Pt and Co/Pt;an increased atomic ratio on the surface for Co/Pt results in an activity enhancement,which is contrary to the effect of the increase of Ru/Pt atomic ratio.     

Collider search of light dark matter model with dark sector decay

We explore the possibility that the dark matter relic density is not produced by a thermal mechanism directly, but by the decay of other heavier dark-sector particles which themselves can be produced by the thermal freeze-out mechanism. Using a concrete model with light dark matter from dark sector decay, we study the collider signature of the dark sector particles associated with Higgs production processes. We find that future lepton colliders could be a better place to probe the signature of this kind of light dark matter model than hadron colliders such as LHC. Also, we find that a Higgs factory with center-of-mass energy 250 GeV has a better potential to resolve the signature of this kind of light dark matter model than a Higgs factory with center-of-mass energy 350 GeV.     

Fingerprinting and simultaneous determination of alkaloids in Picrasma quassioides from different locations by high performance liquid chromatography with photodiode array detection

A simple and sensitive method was developed and validated for profiling and simultaneous quantitation of seven alkaloids (6-hydroxy-β-carboline-1-carboxylic acid, β-carboline-1-carboxylic acid, β-carboline-1-propanoic acid, 3-methylcanthin-5,6-dione, 5-hydroxy-4-methoxycanthin-6-one, 1-methoxycarbony-β-carboline, and 4,5-dimethoxycanthin-6-one) in Picrasma quassioide grown in different locations by high-performance liquid chromatography with photodiode array detection. The analysis was conducted on a Phenomenex Gemini C(18) column at 35°C with mobile phase of 25 mM aqueous ammonium acetate (pH 4.0, adjusted by glacial acetate acid) and acetonitrile. A common fingerprint chromatograph under 254 nm consisting of 27 peaks was constructed for the evaluation of the similarities among 31 P. quassioide samples. Samples from Guangdong and Guangxi Provinces were found to be within group linkage and showed significant difference from that of Jiangxi Province origin by using principal component analysis and hierarchical clustering analysis. In addition, the seven alkaloids were identified by electrospray ionization mass spectrometry and comparing with reference standards and literature data. All of them were determined simultaneously using the established HPLC method. This rapid and effective analytical method could be employed for quality assessment of P. quassioide, as well as pharmaceutical products containing this herbal material.     

One-dimensional lanthanide complexes bridged by nitronyl nitroxide radical ligands with non-chelating nitrogen donors: Structure and magnetic characterization

A series of new lanthanide-radical complexes [{Ln(hfac)3}2(NITPhIM)2] (Ln = Nd (1), Eu (2), Tb (3), Er (4); hfac = hexafluoroacetylacetonate; NITPhIM = 2-[4-(1-imidazole)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been prepared and characterized. Single crystal X-ray diffraction analyses reveal that these complexes are isostructural with one-dimensional chain structures. These consist in Ln(hfac)3 units bridged by the paramagnetic ligands by the means of coordination of their nitronyl nitroxide groups and imidazole rings. Interestingly, each Ln ion is either bound to two nitronyl nitroxide groups or to two imidazole units, and the different Ln centers alternate along the chain. Magnetic studies show that complex 3 exhibits a single-chain magnet behavior.     

Calixarene-supported hexadysprosium cluster showing single molecule magnet behavior

The syntheses, crystal structures, magnetic and luminescent properties of three isomorphous compounds [Ln III 6 (μ 4-O) 2 (C4A) 2-(NO 3 ) 2 (HCOO) 2 (CH 3 O) 2 (DMF) 4 (CH 3 OH) 4 ] (Ln = Gd (1), Tb (2) and Dy (3); H 4 C4A = p-tert-butylcalix[4]arene) are reported. These three compounds are featured with the sandwich-like units constructed by two tail-to-tail calixarene molecules and an in-between Ln III 6 octahedron. The Dy III compound exhibits both single molecule magnet behavior and photoluminescence.