激光吸收铒掺杂上转换材料的光谱特性实验分析

采用湿化学法制备了铒掺杂氧化钇上转换纳米粉体材料.研究了不同掺杂浓度、掺杂元素种类对材料显微结构、物相组成和光谱特性的影响.结果表明,通过控制掺杂元素的种类、掺杂浓度可以实现对光谱性能（包括光谱反射系数和上转换光谱）的调控.实验表明,该材料对106 μm激光具有较好的吸收性能. 关键词： 铒掺杂氧化钇纳米粉体 上转换材料 激光与红外复合隐身 光谱反射系数     

Four-wave parametric conversion of femtosecond laser pulse in a filament induced in a solid target

Nonlinear interaction of two femtosecond laser pulses in a filament, induced by one of them inside a fused silica plate, leads to generation of the new spectral components. These spectral components reach hundreds of nanometers bandwidth. Their spatial and spectral properties can be explained by four-wave parametric coupling in the filament. The energy measurements indicate the high efficiency of this process.     

Hybrid division of aperture/division of a focal-plane polarimeter for real-time polarization imagery without an instantaneous field-of-view error

The direct, instantaneous measurement of the Stokes parameters of optical radiation is not possible using only a single detector. To infer the Stokes parameters in an image, the optical intensity must be modulated in time, space, or spectral characteristics and multiple measurements must be made on a pixel-by-pixel basis across the scene. Most existing imaging polarimetry strategies generally suffer from either spatial or temporal misregistration. Those strategies that do not suffer from misregistration have severe restrictions placed on the spectral properties of the illumination and/or optical system. A hybrid polarimeter is proposed that can be used for broadband imaging applications that, in principle, can be made without any temporal or spatial misalignment and that does not require detailed knowledge of the spectral properties of the radiation. The strategy uses arrays of microlenses and micropolarizers to create a high-resolution spatial array of nonimaging division of aperture polarimeters.     

Spectral models of additive and modulation noise in speech and phonatory excitation signals

The article presents spectral models of additive and modulation noise in speech. The purpose is to learn about the causes of noise in the spectra of normal and disordered voices and to gauge whether the spectral properties of the perturbations of the phonatory excitation signal can be inferred from the spectral properties of the speech signal. The approach to modeling consists of deducing the Fourier series of the perturbed speech, assuming that the Fourier series of the noise and of the clean monocycle-periodic excitation are known. The models explain published data, take into account the effects of supraglottal tremor, demonstrate the modulation distortion owing to vocal tract filtering, establish conditions under which noise cues of different speech signals may be compared, and predict the impossibility of inferring the spectral properties of the frequency modulating noise from the spectral properties of the frequency modulation noise (e.g., phonatory jitter and frequency tremor). The general conclusion is that only phonatory frequency modulation noise is spectrally relevant. Other types of noise in speech are either epiphenomenal, or their spectral effects are masked by the spectral effects of frequency modulation noise.     

Spectral properties of stochastic electromagnetic twist anisotropic Gaussian-Schell model beam truncated by a slit aperture propagating in turbulent atmosphere

With the help of the tensor method, the cross-spectral density matrix for the stochastic electromagnetic twist anisotropic Gaussian-Schell model (ETAGSM) beam truncated by a slit aperture propagating in turbulent atmosphere are derived. The spectral properties of this kind of beam are investigated in detail. It is shown by numerical results and analysis that the affection of the slit aperture on the spectral properties of the stochastic ETAGSM beam is obvious in the near field; while in the far field, the atmospheric turbulence plays an important role; the source beam's coherence can weaken the affection of the slit aperture and the atmospheric turbulence on the spectral properties of the stochastic ETAGSM beam truncated by a slit aperture propagating in turbulent atmosphere, while the twist properties of the source beam can strong the affection of the slit aperture on the spectral properties in the near field. Also, the spectral degree of polarization and normalized spectral density distributions and corresponding contour graphs of the stochastic ETAGSM beam truncated by a slit aperture propagating in turbulent atmosphere and free space at different propagation distances are investigated in detail.     

Normal random matrix ensemble as a growth problem

In general or normal random matrix ensembles, the support of eigenvalues of large size matrices is a planar domain (or several domains) with a sharp boundary. This domain evolves under a change of parameters of the potential and of the size of matrices. The boundary of the support of eigenvalues is a real section of a complex curve. Algebro-geometrical properties of this curve encode physical properties of random matrix ensembles. This curve can be treated as a limit of a spectral curve which is canonically defined for models of finite matrices. We interpret the evolution of the eigenvalue distribution as a growth problem, and describe the growth in terms of evolution of the spectral curve. We discuss algebro-geometrical properties of the spectral curve and describe the wave functions (normalized characteristic polynomials) in terms of differentials on the curve. General formulae and emergence of the spectral curve are illustrated by three meaningful examples.     

On New Relations Between Spectral Properties of Jacobi Matrices and Their Coefficients

We study the spectral properties of Jacobi matrices. By using ``higher order' trace formulae we obtain a result relating the properties of the elements of Jacobi matrices and the corresponding spectral measures. Complicated expressions for traces of some operators can be magically simplified allowing us to apply induction arguments. Our theorems are generalizations of a recent result of R. Killip and B. Simon [17].     

谱线自动提取的小波变换零交叉点方法

将原始光谱进行小波变换,然后研究谱线在小波变换域内呈现的特性,通过引入上、下零交叉点的概念,分析并得到吸收线和发射线分别对应于不同类型的零交叉点的结论。提出一种小波变换零交叉点方法用于提取谱线和拟合连续谱,与传统方法相比,该方法可以同时得到连续谱和谱线,并且无需专门去噪处理,克服了传统方法因拟合连续谱失真和去噪过程中带来的误差导致提取谱线不准确的缺点。通过对恒星、近邻星系等的试验表明,该方法是有效的, 对特征参数计算和基于谱线的光谱分类是非常有利的。     

A New Algorithm for Development of Dynamic Cyclic Shift Code for Spectral Amplitude Coding Optical Code Division Multiple Access Systems

Abstract

This article presents a new code—the dynamic cyclic shift code—for spectral amplitude coding–optical code division multiple access systems. One of the important properties of the dynamic cyclic shift code is that the number of users can be increased without increasing the weight value. System performance was evaluated by using both theoretical analysis as well as the simulation experiment. The analysis results show that the proposed dynamic cyclic shift code can support more users in spectral amplitude coding–optical code division multiple access systems compared to spectral amplitude coding–optical code division multiple access codes. It was ascertained by performance evaluation that the dynamic cyclic shift code possesses ideal properties for use in spectral amplitude coding–optical code division multiple access systems.     

Spectral Automorphisms in Quantum Logics

In quantum mechanics, the Hilbert space formalism might be physically justified in terms of some axioms based on the orthomodular lattice (OML) mathematical structure (Piron in Foundations of Quantum Physics, Benjamin, Reading, 1976). We intend to investigate the extent to which some fundamental physical facts can be described in the more general framework of OMLs, without the support of Hilbert space-specific tools. We consider the study of lattice automorphisms properties as a “substitute” for Hilbert space techniques in investigating the spectral properties of observables. This is why we introduce the notion of spectral automorphism of an OML. Properties of spectral automorphisms and of their spectra are studied. We prove that the presence of nontrivial spectral automorphisms allow us to distinguish between classical and nonclassical theories. We also prove, for finite dimensional OMLs, that for every spectral automorphism there is a basis of invariant atoms. This is an analogue of the spectral theorem for unitary operators having purely point spectrum.     

Modulation in the statistical properties of stochastic electromagnetic beams through an electromagnetic induced transparency atomic vapor

We report analytical expressions for the elements of the 2 × 2 cross-spectral density matrix of a stochastic electromagnetic beam passing through an electromagnetic induced transparency (EIT) atomic vapor. By use of the derived formulas the changes in the spectral density, the spectral degree of coherence, and the spectral degree of polarization of such a beam on propagation can be studied in detail. Numerical examples show that the statistical properties of the stochastic electromagnetic beam can be modulated by the Rabi frequency of the control light when the beam propagates through the EIT atomic vapor.     

Random-wavelength solid-state laser

The spectral properties of a diode-pumped Yb:Y2O3 ceramic laser are reported. We show experimentally that the instantaneous emission wavelengths of the laser change randomly with time, whereas its emission has fixed well-defined transverse modes. The central wavelength of the laser emission also shifts prominently with the increase of intracavity light intensity. It is found that the spectral properties of the laser can be explained well based on the strong reabsorption of light in the gain medium.     

高光谱遥感信息中的特征提取与应用研究

特征提取、度量与分析是高光谱遥感应用的基础.面向高光谱遥感数据的特点, 将光谱特征划分为点尺度、面尺度和体尺度三个尺度的特征.基于特征属性与算法原理, 构建了光谱曲线特征、光谱变换特征和光谱度量特征三个层次的高光谱遥感光谱特征体系, 并对光谱特征提取与应用进行了深入探讨.光谱曲线特征包括直接光谱编码、光谱反射与吸收特征等, 光谱变换特征包括植被指数、导数光谱等, 光谱度量特征则包括光谱角、SID、相关系数和距离等.在分析特征算法原理的同时对其特点和应用进行了探讨.试验表明四值编码、光谱角和SID在应用中能够取得较好的效果.     

芯-壳结构复合纳米颗粒

芯－壳结构复合纳米颗粒因其独特结构而具有许多奇异的性质，尤其体现在可人工设计和可控的光学性质上：根据不同的性质要求，通过改变组分和壳层与芯部的相对尺寸来实现光学性质在很宽波段范围内的可调特性，这一特性在光敏器件（如光开关，光过滤器）以及下一代的纳米光子光等很多领域有着广阔的应用前景，并在目前红外材料的改性上也会大显身手，文章介绍了几种芯－壳复合纳米颗粒的合成及其性质研究现状，并作相应的展望。     

Multiple spectral window mirrors based on Fibonacci chains of dielectric layers

The unique properties of one-dimensional (1D) Fibonacci chains of dielectric layers are experimentally demonstrated and exploited for the design of new mirrors with multiple reflection spectral windows. The new mirror structures are simple, straightforward to make and enable a wide variety of multiple spectral window device performance to be achieved. By changing the thickness of the layers or the order of the Fibonacci chain, tens or even hundreds of windows can be obtained with the same approximate reflectivity over a very broad spectral region. These mirrors have numerous applications in photonics and optoelectronics.     

Dynamic properties of three-dimensional piezoelectric Kagome grids

Piezoelectric Kagome grids can be considered as a kind of functional material because they have vibration isolation performance and can transform mechanical energy to electric energy. In this study, the dynamic properties of three-dimensional (3D) piezoelectric Kagome grids without and with material defects are studied based on the frequency-domain responses. The spectral element method (SEM) is adopted to solve a 3D piezoelectric beam which contains bending components in two planes, tensional components, and torsional components. The dynamic stiffness matrix of a spectral piezoelectric beam is derived. Highly accurate solutions in the frequency-domain are obtained by solving the equation of motion of the whole structure. Compared with the results from the FEM and those in the existing literature, it can be seen that the SEM can be effectively used to study the 3D piezoelectric Kagome grids. The band-gap properties of Kagome grid and defect state properties of Kagome grid with material defects are analyzed. The effect of the piezoelectric parameter on the band-gap property is investigated further.     

中阶梯光栅衍射效率及杂散光检测系统设计

中阶梯光栅具有刻线密度低、闪耀角度大、衍射级次高、光谱范围宽、色散率大、光谱分辨率高等一系列突出优点,近年来由于其优良的性能而倍受青睐。作为评价中阶梯光栅质量的衍射效率和杂散光系数直接体现了中阶梯光栅的光学性能,能够准确地进行中阶梯光栅衍射效率和杂散光系数的测量是光栅应用的前提。鉴于此,基于中阶梯光栅的衍射理论创造性地提出用一套系统对中阶梯光栅的衍射效率和杂散光系数进行检测,该系统引入双轨结构,具有结构简单新颖、一机多能等优点。通过理论分析和计算,确定了检测系统的结构参数,设计结果表明： 该检测系统可用于测量190～1 100 nm光谱范围内的中阶梯光栅绝对衍射效率,同时也可用于测量200～800 nm光谱范围内的中阶梯光栅杂散光系数,实现了将衍射效率测量和杂散光测量集于一体的设计思想。     

Gamow Vectors for Resonances: A Lax-Phillips Point of View

Results from the Lax-Phillips Scattering Theory are used to analyze quantum mechanical scattering systems, in particular to obtain spectral properties of their resonances which are defined to be the poles of the scattering matrix. For this approach the interplay between the positive energy projection and the Hardy-space projections is decisive. Among other things it turns out that the spectral properties of these poles can be described by the (discrete) eigenvalue spectrum of a so-called truncated evolution, whose eigenvectors can be considered as the Gamow vectors corresponding to these poles. Further an expansion theorem of the positive Hardy-space part of vectors Sg (S scattering operator) into a series of Gamow vectors is presented.     

体布拉格光栅用于高功率光谱组束的研究

使用透射型体布拉格光栅组束两束光纤激光,实现了856 W光谱组束输出。总的光谱组束效率为73.7%,组束光束的横向质量因子为7.9,纵向质量因子为2.7。研究结果显示,虽然体光栅的角色散严重影响衍射光束的光束质量,但其并不影响透射光束的光束特性。由于当前宽谱光纤激光器的输出功率远大于窄线宽输出,使用宽谱光纤激光器(光谱带宽超过4nm)作为透射光束,能够在不降低组束效率和组束光束质量的前提下,有效提升使用体布拉格光栅进行光谱组束的总输出功率。     

Luttinger liquids with boundaries: Power-laws and energy scales

We present a study of the one-particle spectral properties for a variety of models of Luttinger liquids with open boundaries. We first consider the Tomonaga-Luttinger model using bosonization. For weak interactions the boundary exponent of the power-law suppression of the spectral weight close to the chemical potential is dominated by a term linear in the interaction. This motivates us to study the spectral properties also within the Hartree-Fock approximation. It already gives power-law behavior and qualitative agreement with the exact spectral function. For the lattice model of spinless fermions and the Hubbard model we present numerically exact results obtained using the density-matrix renormalization-group algorithm. We show that many aspects of the behavior of the spectral function close to the boundary can again be understood within the Hartree-Fock approximation. For the repulsive Hubbard model with interaction U the spectral weight is enhanced in a large energy range around the chemical potential. At smaller energies a power-law suppression, as predicted by bosonization, sets in. We present an analytical discussion of the crossover and show that for small U it occurs at energies exponentially (in -1/U) close to the chemical potential, i.e. that bosonization only holds on exponentially small energy scales. We show that such a crossover can also be found in other models. Received 8 February 2000 and Received in final form 25 April 2000