Light quenching of tetraphenylbutadiene fluorescence observed during two-photon excitation

We observed the steady-state and time-resolved emission of tetraphenylbutadiene (TPB) whea excited by simultaneous absorption of two photons (514 to 610 nm). The intensity initially increased quadratically with laser power, as expected for a two-photon process. At higher laser powers the intensity increases in TPB were subquadratic. The intensity and anisotropy decay times of TPB were unchanged under the locally intense illumination. Importantly, the time zero anisotropy of TPB was decreased under conditions where the intensity was subquadratic. Furthermore, the subquadratic dependence on incident power was not observed for two-photon excitation of 2,5-diphenyloxazole (PPO), for which the incident wavelength does not overlap with the emission spectrum. These results are consistent with stimulated emission (light quenching) of TPB at high laser intensities. The phenomenon of light quenching may be important for other fluorophores used in biochemical research, particularly for the high local intensities used for two-photon excitation.     

基于锥形透镜的光线入射角度测量系统设计与研究

为测量光线入射角度，设计了一种基于锥形透镜的新型光线入射角度测量系统。利用光阑、锥形透镜和图像接收装置，获取待测光线通过光阑射入锥形透镜后经过多次的折射和反射，在图像接收装置上得到的复杂光斑图像，通过图像处理得到光斑图像特征信息，进而求解光线入射角度。采用锥形透镜的测量方案，角度测量范围可达80°，精度最高可达 (1×10?4)″。该方案结构简单、体积小且不需要进行繁琐的安装调试。与现有的单光点测量等方法相比，该方案中锥形透镜具有角度放大作用，可大幅度提高测量精度且具有大视场；图像传感器像素分辨率对测量结果影响较小，系统光通量大，容易获得较高的信噪比。     

Mie理论在生物组织散射特性分析中的应用

根据等效颗粒散射模型，运用经典的Mie理论，对生物组织的散射相函数、各向异性因子及散射系数进行了数值计算.计算结果表明：可见光照射生物组织时，各向异性因子、散射系数随等效颗粒直径增大而增大；等效颗粒直径较小时，各向异性因子、散射系数随入射光波长增大而单调减小；随着等效颗粒直径增大，各向异性因子、散射系数随入射光波长变化不再具有单调性.上述计算结果可合理解释公布的实验结果. 关键词： 生物组织 散射 Mie理论 等效颗粒     

Anomalous birefringence of light in free-standing samples of porous silicon

The birefringence of light in freely suspended samples of porous silicon is observed and investigated. The effect is interpreted as “shape birefringence,” i.e., the effect caused by the structure of a material consisting of anisotropic formations with sizes less than the wavelength of the light and with a predominant orientation. It is checked experimentally that the samples do not possess optical activity or optical anisotropy in the plane of the porous-silicon film. It is determined that the effect is observed for polarization of incident light that rules out the possibility of observing birefringence in a uniform optical medium, and it is not observed in the conventional experimental geometry. Qualitative explanations are given for the anomalous character of the observed defect.     

A Model of Irradiance Distribution for a Directed Point Source in an Infinite Weakly Absorbing Turbid Medium

We propose simple models describing the irradiance distributions for a unidirectional point source in an infinite weakly absorbing turbid medium and also for a narrow light beam obliquely incident on the boundary of a semi-infinite turbid medium. These models involve the same optical parameters of the medium as the formulas of the diffusion approximation of radiation-transport theory. At the same time, the condition of weak anisotropy of the radiation field does not limit the applicability of our models.     

Polarization-independent modulation of light in gyrotropic cubic crystals

Polarization-independent modulation of light in gyrotropic cubic crystals is investigated in the Bragg and intermediate diffraction regimes. It is found that, for crystals with considerable specific rotation, the photoelastic anisotropy is suppressed by the circular anisotropy and the observed diffraction efficiency depends weakly on the polarization azimuth of the incident light. Good agreement is obtained between modulation parameters calculated theoretically on the basis of the coupled wave theory and experimental results for a bismuth silicate crystal in the intermediate diffraction regime.     

Mapping local retardance in birefringent samples using polarization sensitive optical coherence tomography

We proposed a method to extract depth-resolved local retardance in birefringent samples from conventional polarization-sensitive optical coherence tomography (PSOCT) that uses one circularly polarized incident light. Despite the wide use of such PSOCT systems in characterizing birefringent samples, the measured cumulative retardance does not represent the true cumulative retardance when optical axis varies with depth. A Jones calculus based algorithm was designed to derive the local depth-resolved retardance from conventional cumulative PSOCT results. The algorithm was tested in samples with homogeneous optical axis as well as samples with depth-dependent optical axis.     

Analysis of anisotropic matrix elements in GaAs quantum wells oriented in the [112] crystal axis

We report the experimental confirmation of optical anisotropy in [112]-oriented GaAs/(Al,Ga) As quantum well structures. A theoretical calculation of the momentum matrix elements predicts the existence of this anisotropy and its dependence on the polarization of the incident radiation. It is found that recombination emission from photoluminescence excitation for the fundamental e→hh1 transition is anisotropic for incident light polarized along the two orthogonal [1¯10] and [111¯] crystallographic directions. No anisotropy is found in identically prepared [001]-oriented structures either theoretically, or experimentally.     

Unsupervised Anomaly Detection with Distillated Teacher-Student Network Ensemble

We address the problem of unsupervised anomaly detection for multivariate data. Traditional machine learning based anomaly detection algorithms rely on specific assumptions of normal patterns and fail to model complex feature interactions and relations. Recently, existing deep learning based methods are promising for extracting representations from complex features. These methods train an auxiliary task, e.g., reconstruction and prediction, on normal samples. They further assume that anomalies fail to perform well on the auxiliary task since they are never trained during the model optimization. However, the assumption does not always hold in practice. Deep models may also perform the auxiliary task well on anomalous samples, leading to the failure detection of anomalies. To effectively detect anomalies for multivariate data, this paper introduces a teacher-student distillation based framework Distillated Teacher-Student Network Ensemble (DTSNE). The paradigm of the teacher-student distillation is able to deal with high-dimensional complex features. In addition, an ensemble of student networks provides a better capability to avoid generalizing the auxiliary task performance on anomalous samples. To validate the effectiveness of our model, we conduct extensive experiments on real-world datasets. Experimental results show superior performance of DTSNE over competing methods. Analysis and discussion towards the behavior of our model are also provided in the experiment section.     

Light scattering from anisotropic particles: propagation,localization, and nonlinearity

Plasmon resonances and extraordinary light scatterings of a nanoparticle with radial anisotropy are studied and summarized. The coupling between localized surface plasmons and far‐field quantities is discussed. It is found that the presence of radial anisotropy redistributes the localization of plasmons and also results in certain novel phenomena in the far zone, which provide the possibility of scattering control such as electromagnetic transparency, enhanced scattering cross section, etc. The nonlinear optical response is explored in order to yield deeper physical insight into the interaction between plasmons and incident light.     

利用宽带信号统计的鱼群资源量反演方法

针对鱼群资源量反演问题,建立了一种基于宽带回波信号统计的反演方法。首先考虑自然状态下鱼群活动的随机性,并通过回波信号波形简化,实现了对鱼群宽带回波脉冲压缩输出信号的建模。然后以信号强度变异系数作为统计特征量,完成了统计特征量与鱼群资源量的数值关系模型的推导。仿真与海试实验结果表明该方法能有效实现鱼群资源量的反演,且比已有的窄带反演方法误差更小、统计所需样本更少。与主流的回波积分法相比,该方法不依赖鱼群先验知识,且无需计算声呐信号的绝对声学量,具有很好的应用潜力。      

一种高精度线结构光视觉传感器现场标定方法

针对现有线结构光视觉传感器标定方法存在的局限性,提出一种不需要求解光平面标定点的标定方法.根据光条图像求解平面靶标上光条在摄像机坐标系下的Plücker矩阵.在视觉传感器前合适位置将平面靶标摆放多次,联立所有光条空间直线的Plücker矩阵,求解光平面在摄像机坐标系的平面方程.最后通过非线性优化方法得到光平面方程在最大似然准则下的最优解.在标定过程中,所有光条点都参与光平面参数的计算过程,因此该方法标定结果精度高、稳健性强.实验证明,与现有方法相比该方法标定精度提高30%左右.     

纳米ZnO薄膜的反射及偏振特性研究

用电子束蒸发镀膜法制备了纳米ZnO薄膜．通过测量其X射线衍射谱,计算出纳米ZnO颗粒的平均粒径大小为30nm．实验研究了纳米ZnO薄膜的反射和偏振性质,结果表明：当振动方向平行于入射面的线偏振光（简称P光）入射纳米ZnO薄膜时,不存在严格意义上的布儒斯特角,但对于入射角却存在一个临界角β．当入射角小于β时,反射光的振动面随着入射角的增大向左旋转;当入射角大于β时,振动面转而向右旋转;当振动方向垂直于入射面的线偏振光（简称S光）入射纳米ZnO薄膜时,反射光的振动面始终向左旋转．     

浅表组织后向散射检测中偏振门的蒙特卡罗研究

已有实验表明偏振门和斜入射技术能有效地抑止深层散射光子,实现浅表组织光学特性的检测。采用蒙特卡罗方法,分析了斜入射、偏振门的特性,研究了组织光学参量和入射角等参量对平均探测深度的影响。结果表明,组织的各向异性因子和入射角对平均探测深度影响较大。当各向异性因子较小(小于0.8)或者入射角较大(大于1.4 rad)时,组织的平均探测深度能满足小于2倍平均自由程的要求。偏振门和斜入射技术均可使探测光子经历的散射次数和探测深度有明显减小,因此,结合偏振门和斜入射技术能够更有效地分辨来自浅层的信号光,抑止来自深层的背景光。     

Out-of-plane emission of nuclear matter in Au+Au collisions between 100 and 800 AMeV

We present new experimental results concerning the azimuthal distributions of proton-likes, light and intermediate mass fragments at midrapidity for Au(100–800 A MeV) +Au collisions measured with the FOPI phase-I detector at GSI in Darmstadt. The azimuthal distributions are investigated as a function of the collision centrality, the incident energy, the fragment charge and transverse momentum. The azimuthal anisotropy is maximum for impact parameters around 7 fm. Intermediate mass fragments present a stronger out-of-plane emission signal than light fragments and a saturation is reached for Z ⩾ 4. The azimuthal anisotropy increases with the fragment transverse momentum and decreases as the incident energy increases. The azimuthal anisotropy of Z = 2 particles investigated as a function of the scaled fragment transverse momentum follows an universal curve for bombarding energies between 250–800 A MeV. A signature for a transition from in-plane to out-of-plane emission is evidenced at the lowest beam energies.     

偶氮苯介晶基元取向方式对其取向稳定性影响

根据取向透射率变化研究了偶氮苯侧链液晶聚合物在不同光照功率条件下的取向,用锥光干涉法表征了侧链介晶基元的取向方向,并研究了升温对取向膜的稳定性影响.实验结果表明介晶基元的取向速度和取向度都随光照时间和光照功率增加而增加|超过一定阈值功率（20 mW/cm2）时,随着光照时间延长薄膜的透射率（取向度）反而降低.高功率光照使侧链介晶基元发生了面内和面外两种取向,面外取向使聚合物膜的透射率降低.面外倾斜取向的介晶基元不稳定,在取向未达到饱和时停止光照,倾斜取向的介晶基元容易发生解取向,而面内取向的介晶基元则能维持取向的状态.用不饱和取向的方法,在光照功率为 20 mW/cm2时,取向时间缩短为饱和取向的1/20,薄膜的取向度提高1.3倍.4 ms的一次曝光足以使聚合物膜产生可读出、稳定的面内取向,取向的结果能保持2年不发生变化.     

非晶合金带制备态平面磁各向异性与技术磁性的关系

用磁转矩和磁化功方法测定Fe₄₀Ni₄₀P₁₂B₈和(Fe_0.1CO_0.5Ni_0.4)₇₈Si₆B₁₆非晶态合金带在制备态及退火后的磁各向异性常数。结果表明,用磁转矩方法测定的制备态非晶带中的平面磁各向异性常数,其中大部分是不因退火而改变的,这部分的磁各向异性对合金的技术磁化曲线无明显影响 关键词：     

单顶角结构LED背光模组的设计与优化

由于LED（发光二极管）具有寿命长、色域宽、功耗低和环保（传统的光源CCFL含有汞气）等特性,在背光模组中采用LED代替CCFL（冷阴极荧光灯）是一种趋势。采用单光源顶角入射结构设计一个5.08cm(2inch)液晶背光模组。针对LED作为点光源带来的亮度不均匀的问题,采用旋转LED的入射角度和区域分割设计的方法,有效地解决了LED液晶背光模组中存在亮斑和暗区等不良的现象。通过模拟实验,可以得到光源出射均匀度为80.06%的导光板。     

Interference spectroscopy with coherent anti‐Stokes Raman scattering of noisy broadband pulses

We propose a new technique for comparing two Raman active samples. The method employs optical interference of the signals generated via coherent anti‐Stokes Raman scattering (CARS) of broadband laser pulses with noisy spectra. It does not require spectrally resolved detection, and no prior knowledge about either the Raman spectrum of the samples or the spectrum of the incident light is needed. We study the proposed method theoretically and demonstrate it in a proof‐of‐principle experiment on toluene and o‐xylene samples. Copyright © 2011 John Wiley & Sons, Ltd.     

Anisotropy of light propagation in thin opal films

Thin opal films are prepared by crystallization in a moving meniscus, and their optical transmission spectra are recorded in polarized light and studied. It is shown that the anisotropy of light propagation in the films is unambiguously related to the photonic band structure of opal and depends on the angle of incidence, the orientation of the incidence plane with respect to the opal lattice, and the wavelength and polarization of the incident light. Azimuthal diagrams of transmitted polarized light are constructed in the range of photonic band gaps of three orders for oblique incidence of a light beam. The anisotropy is found to vary with the light wave-length independently in perpendicular polarizations. A model of the band structure of opal wherein opal is represented as an fcc lattice of close-packed spheres adequately describes the optical transmission of opal films only in the range of the first-order photonic band gap.