低密度稀土氧化物基气凝胶靶的研制

低密度的高原子序数元素氧化物气凝胶由于前驱体形成端基双键而易于收缩和开裂。通过调控配位环境结合无机分散溶胶凝胶法,制备了稀土氧化物气凝胶。氧化镧基气凝胶和氧化钇基气凝胶块体的成型性好,最低密度分别为0.05g·cm-3和0.06g·cm-3。其成分分别为六方相的La(OH)3和六方相的Y(OH)3,而聚丙烯酸中的羧基与稀土离子之间以桥接的方式进行配位。两种气凝胶均存在明显的多级结构,氧化镧基和氧化钇基气凝胶的初级粒子分别为纤维状和片/球混合形貌,而其二级粒子均为球形。两种气凝胶的比表面积分别为229.1m2·g-1和229.6m2·g-1。该方法制备的稀土氧化物气凝胶具有低的密度和纳米尺度的均匀性,在背光源中有潜在的应用。     

对流层高度大气温度、湿度和气溶胶的拉曼激光雷达系统

为了实现大气温度、水汽(相对湿度)和气溶胶的实时同步探测研究,成功研制了一台日常观测的多参数探测拉曼激光雷达,采用高性能二向色镜和窄带干涉滤光片组成高光谱分辨率高效率拉曼分光系统,实现独立5通道大气回波信号的高精细分光和高效率提取,并研发了多参数同步反演算法,获得了大气水汽密度、温度和气溶胶消光系数廓线,结合水汽密度和温度得到了同时刻大气相对湿度的垂直变化特性。利用该系统在晴天和有云条件下对西安局地进行初步实验观测,获得温湿度及气溶胶廓线以及云层内水汽与逆温层的高度关系。实验结果表明,在探测时间15 min和激光能量150 m J的条件下,系统在晴天条件可实现高度16 km以下大气温度和湿度的同步探测,在有云条件下系统可实现大气底层和云层顶逆温层的精确探测,并可获得高层云层内和水汽层内大气水汽密度和相对湿度的同步增长趋势。实验数据与当地探空数据的多次随机比对在大气温度、湿度廓线上取得了较好的一致性,充分验证了该拉曼激光雷达实现对流层高度大气多参数同步探测的有效性和系统的可靠性。使用该系统可有效开展区域性大气的观测研究,为大气气候变化以及雾霾生消过程的研究提供可靠的实时探测数据。     

高功率钕玻璃啁啾脉冲放大系统光谱整形

增益窄化效应限制了啁啾脉冲放大系统输出的最短脉冲宽度,需要对注入放大系统的种子啁啾脉冲进行光谱整形,以保证放大后的啁啾脉冲光具有足够的带宽并满足特定的光谱分布.理论上假定放大后啁啾脉冲的光谱分布为高斯分布或超高斯分布,对"百焦耳级钕玻璃啁啾脉冲放大系统"进行逆运算.研究发现,所需种子啁啾光的能量、带宽以及压缩后脉冲的信噪比都与该分布密切相关.通过光谱整形,使放大后的啁啾脉冲光的光谱分布为二阶超高斯分布.能够获得小于400 fs高信噪比的超短脉冲输出,此时所需种子啁啾脉冲能量仅为33μJ,带宽14 nm,在装置前级注入能力的范围之内.为百焦耳装置光谱整形实验的开展提供了理论指导.     

高斯光束对标准硅球直径测量的影响分析

针对高精度硅球直径测量系统的特点,分析平面波反射光的多光束干涉和双光束干涉,以及正入射时高斯光束反射光中心的多光束干涉和双光束干涉,对不同条件下的高斯光束反射光中心的干涉光强进行了数值模拟.对采用五步相移算法时高斯多光束干涉的影响进行了研究,给出了特定参数条件下不同束腰ω0和传播距离z时的最大相位误差,当ω0=5 mm,z=2000 mm时的最大相位误差达0.08%.     

氢同位素氚水T2 O((X)1A1)的解析势能函数

获得T2 O(X1A1)解析势能函数的主要困难在于Born-Oppenheimer近似下T2 O(X1A1)与H20(X1A1)势能函数的不可区分性.然而,在Bom-Oppenheimer近似下,分子势能函数实际上是键长、键角这些内坐标的函数,内坐标与核的运动相关,因而与分子振动频率、力常数和同位素质量有关.基于这种关系.用核运动效应对Born-Oppenheimer近似下T2 O(X1A,1)的电子能量进行修正,可获得体现同位素氢和氚质量差异的力常数,其结果与有关文献值是相符的.然后用多体项展式理论和方法,并考虑T2 O(X1A1)中两体项中的同位素效应,在确定T2 O(X1A1)离解极限和离解能以及计算所有两体项参数的基础上,获得了T2 O(X1A1)的解析势能函数.对应的等值势能图正确反映了T2 O(X1A1)的平衡结构特征,以及T OT→T2O和O2 T2→T2O的反应特点,为后续的碰撞研究提供了条件.     

含圆孔纳米薄膜在拉伸加载下变形机理的原子级模拟研究

采用分子静力学方法结合量子修正的 Sutton-Chen多体势研究了含圆孔的纳米薄膜在单向加载过程中的力学行为,并采用共近邻分析方法研究了薄膜的微结构演化过程.模拟结果表明：孔洞的引入显著地降低了纳米薄膜的杨氏模量和屈服应力;在拉伸过程中,孔洞的形状随着应变的增加逐渐由圆形变为椭圆形,最终孔洞闭合;纳米薄膜在进入塑性变形阶段后,薄膜内部出现原子的堆跺层错,这种层错结构的出现是肖克莱不全位错在薄膜内部沿着{111}面的［112］方向运动的结果. 关键词： 纳米薄膜 力学性质 位错 分子静力学     

Phase matching limitation of high-efficiency second-harmonic generation in both phase- and group-velocity-matched structures

In this paper, we studied efficient second-harmonic generation (SHG) of femtosecond pulses in both phase- and group-velocity-matched structures. Obtained results show that phase matching becomes more critical under conditions required for high levels of conversion efficiency. And the imperfect phase mismatch caused by mismatched group-velocity dispersion (GVD) will limit conversion efficiency as well as bandwidth of generated second-harmonic (SH) pulses. The spectral characteristics of the generated SH pulses and its conversion efficiency in the strong pump regime are investigated in detail. The acceptance bandwidth of nonlinear crystal in the high-efficiency SHG is redefined in the paper, and the definition is much closer to the practical application of design.     

LD-end-pumped Nd:YAP laser operating at 1341.4 nm and doubling of its frequency

We report an LD-end-pumped linearly-polarized continuous-wave (CW) Nd:YAP laser operating at 1341.4 nm. Making use of the plane-concave resonator (T = 2.4%) and the plane-plane resonator (T = 2.6%), we obtain linearly-polarized laser radiation at 1341.4 nm with a power of 3.15 and 2.86 W and corresponding optical slope efficiency of 18.4 and 17.5%, respectively. The effect of the laser oscillation mode on the output is analyzed. An experiment on the intra-cavity frequency doubling with an LBO crystal has been performed, and a laser power of 431 mW in one direction at 670.7 nm was obtained.     

Numerical simulation of soliton and kink density waves in traffic flow with periodic boundaries

The soliton and kink–antikink density waves are simulated with periodic boundaries, by adding perturbation in the initial condition on single-lane road based on a car-following model. They are reproduced in the form of the space–time evolution of headway, both of which propagate backwards. It is found that the solitons appear only near the neutral stability line regardless of the boundary conditions, and they exhibit upward form when the initial headway is smaller than the safety distance, otherwise they exhibit downward form. Comparison is made between the numerical and analytical results about the amplitude of kink–antikink wave, and the underlying mechanism is analyzed. Besides, it is indicated that the maximal current of traffic flow increases with decreasing safety distance. The numerical simulation shows a good agreement with the analytical results.     

Revisiting the security of quantum dialogue and bidirectional quantum secure direct communication

From the perspective of information theory and cryptography, the security of two quantum dialogue protocols and a bidirectional quantum secure direct communication (QSDC) protocol was analyzed, and it was pointed out that the transmitted information would be partly leaked out in them. That is, any eavesdropper can elicit some information about the secrets from the public annunciations of the legal users. This phenomenon should have been strictly forbidden in a quantum secure communication. In fact, this problem exists in quite a few recent proposals and, therefore, it deserves more research attention in the following related study. Supported by the National High Technology Research and Development Program of China (Grant No. 2006AA01Z419), the National Natural Science Foundation of China (Grant Nos. 90604023 and 60373059), the National Research Foundation for the Doctoral Program of Higher Education of China (Grant No. 20040013007), the National Laboratory for Modern Communications Science Foundation of China (Grant No. 9140C1101010601), the Natural Science Foundation of Beijing (Grant No. 4072020) and the ISN Open Foundation