Influence of nonlinear absorption effects on optical bistability in semiconductor ring resonators

We present a theoretical investigation of optical bistability in a nonlinear semiconductor ring resonator, by taking into account the two-photon absorption and the free-carrier absorption. By solving the intensity equation within the ring resonator, a parametric formulation is obtained for describing the bistability relation between the input and the output intensities. Numerical results show that the nonlinear absorption effects can affect the critical points and domain of the optical bistability.     

An anatomically accurate eye model with a shell-structure lens

A human eye model based on anatomically accurate eye model previously proposed by Liou, has been transformed into a new eye model, in which laminated structure of the lens is considered. The crystalline lens is presented in the form of hundreds of shells with rotational symmetry, and with constant index within each shell. The refractive index increases from the cortical shell to the inner one, according to the equation proposed by Smith G. et al. The anterior surface of the lens is prolate, whereas the posterior surface of the lens is oblate which is consistent with the anatomical data. A ray tracing procedure has been applied to study the refractive structure of the eye. The optical characters of the model have been studied. The reason that the wings occur on the spherical aberration curve has been given. And we found that the lens with gradient refractive index and lens with shell structure can give same longitudinal spherical aberration results.     

Optical properties of InGaAsBi/GaAs strained quantum wells studied by temperature-dependent photoluminescence

The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated using the temperature-dependent photoluminescence from 12 K to 450 K.The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K.The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth.The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes.The incorporation of bismuth also induces alloy non-uniformity in the quantum well,leading to an increased photoluminescence linewidth.     

高质量等曲率物参光像面数字全息显微系统

对等曲率物参光像面数字全息显微成像系统进行研究,分析了光路配置方法,推导了系统的点扩散函数,并由此指出了决定系统成像分辨率的因素及系统的成像特点,最后讨论了再现像光场一次位相畸变校正的方法.结果表明,等曲率物参光像面数字全息具有最大的信息容量;该系统的成像分辨率取决于显微物镜的数值孔径和CCD的像元大小,与CCD的光敏面尺寸无关;物体各点中通过显微物镜的所有频率成分均能被系统完全记录与再现,样品被照亮区域的大小对记录条件和再现像质没有影响;等曲率物参光像面数字全息系统是一种优化的全息记录与再现系统,利用该系统可以实现高质量成像.实验结果验证了理论分析的正确性.     

Erdös Rényi随机网络上爆炸渗流模型相变性质的数值模拟研究

基于改进的Newman和Ziff算法以及有限尺寸标度理论, 通过对表征渗流相变特征物理量的序参量、平均集团尺寸、二阶矩、标准偏差及尺寸不均匀性的数值模拟, 分析研究了Erdös Rényi随机网络上Achlioptas爆炸渗流模型的相变性质.研究表明: 尽管序参量表现出了不连续相变的特征, 但序参量以及其他特征物理量仍具有连续相变的幂律标度行为.因此严格地说, Erdös Rényi随机网络中的爆炸渗流相变是一种奇异相变, 它既不是标准的不连续相变, 又与常规随机渗流表现出的连续相变处于不同的普适类. 关键词： Erdös Rényi随机网络 爆炸渗流模型 相变 幂律标度行为     

季节因素对气候网络影响研究

气候网络在地球科学领域研究中是一个新的热点,对于分析和揭示气候场的特征及关联结构具有较强优势.已有气候网络的构建一般选取冬季月份的样本数据,而且在研究中忽略了其他季节月份对气候网络的影响.本文研究了季节因素对气候网络的影响,研究发现:气候网络在不同季节的整体特征参数基本保持稳定,但是网络社团结构以及局部节点拓扑连接随季节变化显著.可以利用这一结论来研究不同季节全球遥相关模态变化情况以及局部地区气候特征随季节变化情况.     

基于法布里-珀罗调谐滤波器的傅里叶域锁模扫频激光光源

报道了一个光纤型1300 nm波段的傅里叶域锁模(Fourier domain mode locking, FDML)扫频激光光源, 用于扫频光学相干层析成像技术 (optical coherence tomography, OCT) 成像. 本实验扫频激光光源采用包含增益介质、调谐滤波器和延迟线组成的长腔激光谐振腔以及光功率增强单元. FDML扫频激光光源具有快速和高度稳定运转模式, 相位稳定性好. 基于法布里-珀罗调谐滤波器(fiber Fabry-Perot tunable filter, FFP-TF)的FDML扫频激光光源扫频范围为130 nm, 半高全宽为70 nm, 输出平均功率是11 mW. 与基于FFP-TF的短腔的扫频光源做了对比研究, FDML扫频光源速度从短腔的8 kHz提高到了48.12 kHz, 对应生物组织OCT成像轴向分辨率为7.8 μm, 比短腔的减小了1.9 μm. 关键词： 光学相干层析技术 扫频激光光源 傅里叶域锁模 法布里-珀罗调谐滤波器     

Off-shell effects in quasielastic electron nucleus scattering

Using the Ward-Takahashi identity, on-shell condition, bound Dirac equation and off-shell expansion, a reduced version of half off-shell virtual photon nucleon vertex has been suggested. The vertex are decomposed into several different order terms: the on-shell terms, first and second off-shell terms. The off-shell behaviour of the form factors is discussed in the one meson loop model. Using the reduced vertex and parametrized off-shell form factors the quasielastic response functions are calculated for several nuclei at ¦q¦–k_f and for⁵⁶Fe at large ¦q¦ up to 1.14 GeV/c and at ?q²=0.9 (GeV/c)². The Coulomb sums are evaluated and a comparison of the theoretical prediction with data is given. The off-shell electron nucleon cross section is calculated and compared with the “cc1” off-shell extrapolation.     

Immunoassays Based on Surface-Enhanced Fluorescence using Gap-Plasmon-Tunable Ag Bilayer Nanoparticle Films

A novel gap-plasmon-tunable Ag bilayer nanoparticle film for immunoassays is demonstrated. Different from a traditional Ag monolayer nanoparticle film, a desired number of polyelectrolyte (PEL) layers are deposited on the nanoparticles before the self-assembly of a second Ag nanoparticle layer. Interestingly, by controlling the number of the PEL interlayers, the gap plasmon between the two Ag nanoparticle layers can be tuned across the visible spectral range. The ability of the presented Ag bilayer nanoparticle films in fluorescence enhancement has been examined experimentally. A maximal enhancement of around 15.4 fold was achieved when 7 layers of polyelectrolyte were used. When this optimal Ag bilayer nanoparticle film was applied to fluorescence immunoassay, a performance with approximately 3.3-fold enhancement was obtained compared with that performed on a traditional glass substrate. The experimental results suggest that the presented gap-plasmon tunable Ag bilayer nanoparticle films have great potential in fluorescence-based immunoassays. The method of the bilayer-film construction presented here also provides new insights into the rational design of the plasmonic substrates.