利用光反射精确测量亚共析碳钢的含碳量

本文从光学角度出发提出了一种经济实用、精度高的测量亚共析碳钢中碳的含量的新方法。阐述了该方法的测量原理，即以金相试样表面对光的反射程度来判定其含碳量，并给出了有关经验公式及数据处理方法。     

Thickness and stacking geometry effects on high frequency overtone and combination Raman modes of graphene

We investigate two high frequency Raman overtone and combination modes of graphene named 2D' and 2D + G bands, and located at ~3240 and ~ 4260 cm^–1, respectively. The graphene thickness and stacking geometry effects for these two modes are systematically studied. The features of the 2D' band, which arises from intravalley double resonance, are not sensitive to the variation of thickness with single Lorentzian peak and fixed linewidth. We explain it theoretically by calculating the phonon dispersion mode in k‐space and find that the flat band region of longitudinal optical phonon near Γ point is the mechanism leading to the 2D' band nonsplit. With the thickness increasing, the band position exhibits blueshift and the linewidth increases for the 2D + G band. With changing thickness and stacking geometry of graphene, the intensities of these two high‐frequency bands show obvious different evolution compared with that of G band. Copyright © 2012 John Wiley & Sons, Ltd.     

pH‐sensing nanostar probe using surface‐enhanced Raman scattering (SERS): theoretical and experimental studies

Local pH environment has been considered to be a potential biomarker for tumor diagnosis because solid tumors contain highly acidic environments. A pH‐sensing nanoprobe based on surface‐enhanced Raman scattering (SERS) using nanostars under near‐infrared excitation has been developed for potential biomedical applications. To theoretically investigate the effect of protonation state on SERS spectra of p‐mercaptobenzoic acid (pMBA), we used the density functional theory (DFT) with the B3LYP functional to calculate Raman vibrational spectra of pMBA‐Au/Ag complex in both protonated and deprotonated states. Vibrational spectral bands were assigned with DFT calculation and used to investigate SERS spectral changes observed from experiment when varying pH value between five and nine. The SERS peak position of pMBA at ~1580 cm⁻¹ was identified to be a novel pH‐sensing index, which has small but noticeable downshift with pH increase. This phenomenon is confirmed and well‐explained with theoretical simulation. The study demonstrates that SERS is a sensitive tool to monitor minor structural changes due to local pH environment, and DFT calculations can be used to investigate Raman spectra changes associated with minor differences in molecular structure. Copyright © 2013 John Wiley & Sons, Ltd.     

Evolution of microstructure and dielectric properties of (LiCe)-doped Na0.5Bi2.5Nb2O9 Aurivillius type ceramics

Aurivillius type (NaBi)_0.5?x(LiCe)_xBi₂Nb₂O₉ ceramics were prepared by the standard ceramics route. The single crystal structural ceramics were achieved for all compositions and lattice distortion was decreased by (LiCe) dopants. The temperature dependent dielectric properties revealed that all compositions possess a high Curie-temperature (>780 °C). A modified Curie–Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition indicating the degree of diffuseness of NBN-based ceramics increased with (LiCe) modifications. The degradation of resistance implied a plausible model that Ce⁴⁺ ions entered into the B-site of the pseudo-perovskite structure and acted as acceptor doping. Further investigation demonstrated that both electrical conduction and dielectric relaxation processes were associated with the oxygen vacancies produced by the substitution of Nb⁵⁺ ions by the Ce⁴⁺ ions.     

高功率905 nm InGaAs隧道结串联叠层半导体激光器

设计出了隧道结串联叠层半导体激光器结构,采用分子束外延进行激光器材料的外延生长,材料经过光刻、腐蚀、欧姆接触、解理、腔面镀高反射/减反射膜、焊装等工艺,制作成条宽200 m、腔长800 m 的半导体激光器。两隧道结激光器在脉冲宽度100 ns,重复频率10 kHz,30 A工作电流下输出功率达到80 W,峰值发射波长为905.6 nm,器件的阈值电流为0.8 A,水平和垂直方向的发散角分别为7.8和25。     

预应力对熔石英损伤的影响

采用ANSYS进行形变-应力模拟。对不同应力状态下的熔石英表面进行三倍频激光损伤测试,结果发现,预加压应力为0~50 MPa时损伤阈值有明显提高的趋势,用应力耦合作用对此给出了解释：0~50 MPa的预加压应力可以降低和抵消激光辐照产生的张应力破坏,大于50 MPa预应力的耦合作用会使得该处机械性能下降,另外,损伤增长在预应力存在时更容易发生。因此,0~50 MPa预加压应力时的表面预应力可以提高熔石英的抗激光辐照能力。     

基于激光诱导偏振光谱与激光诱导荧光技术的CH4/AIR火焰参数测量

建立了激光诱导偏振光谱（LIPS）和激光诱导荧光（LIF）联合的燃烧流场诊断系统,测量了CH4/AIR预混火焰中心不同高度处的OH荧光光谱和激光诱导偏振光谱,计算了OH的浓度及燃烧场温度分布。分析了燃烧炉表面对荧光收集效率的影响,并对两种技术的测量数据进行了分析比对,获得了火焰中心OH密度的分布规律。实验结果表明,联合LIPS和LIF两种技术测量CH4/AIR预混火焰参数是可行的,两种技术测量结果的一致性较好,OH浓度的相对偏差小于5%,温度的相对偏差小于8%。     

一种对物理问题进行数值求解的新方法

用计算机对物理问题进行数值求解,一般采用C语言编程的方法实现[1].这种方法在使用时,存在两个问题:其一是编程工作量大,费时费力;其二是程序的普适性较差,当物理问题的初始条件改变时,需对原程序进行修改.Matlab语言为解决这一问题提供了新的方法.Matlab语言友好的人机界面,简便灵活的操作平台,实用而又齐全的功能,为我们提供了一个良好的工具.     

T-C模型中虚光子过程对光场压缩效应的影响

利用全量子理论,研究非旋波近似下TC模型中受激场的压缩效应.结果表明:非旋波近似下,由于虚光场的影响,Q的演化曲线出现了“小锯齿状”,表现为系统的量子噪声,随着ω和n的增大,量子噪声分别减小和增大,虚光子过程使光场的压缩程度明显加深;研究结果还揭示了原子场耦合系数λ及原子间耦合系数g与光场压缩效应的关系. 关键词： T-C模型 非旋波近似 压缩效应 量子噪声     

HoYb:YVO4的上转换发光研究

研究了960nm激光激发下HoYb双掺钒酸钇晶体HoYb:YVO4的直接上转换增敏发光,发现了Ho3+离子的上转换发光现象,HoYb:YVO4晶体的上转换发光是5F5→5I8最强,而5S2→5I8相对小了一个数量级,这是由于YVO4晶体既有很强的振子强度又有很大的多声子无辐射弛豫造成的. 关键词： 上转换发光 直接增敏(敏化) 钒酸钇YVO4晶体 Ho3+离子