A high-sensitive fiber curvature sensor using twin core fiber-based filter

A high-sensitive fiber curvature sensor is proposed and experimentally demonstrated in a large measurement range by using a twin core fiber (TCF)-based filter as sensor head. Applying the coupled-mode theory and equivalent refractive index model, we theoretically anticipate the “blue shift” of the transmission dips of the TCF-based filter when sensor head is bent. Experimentally, we fabricate an 86.9 mm TCF-based filter with a free spectral range of 49 nm and characterize its curvature performance by measuring the wavelength shift. A nonlinear “blue shift” of the wavelength is observed when we increase the curvature. The relationship between wavelength shift and curvature is a second-order polynomial function. In the range from 0 to 9.30 m^?1, the maximum sensitivity is up to ?14.7 nm/m^?1. The measurement range can be further increased by selecting a shorter TCF.     

Measurement of absolute phase Shift on reflection of thin films using white-light spectral interferometry

A novel method to measure the absolute phase shift on reflection of thin film is presented utilizing a white-light interferometer in spectral domain. By applying Fourier transformation to the recorded spectral interference signal, we retrieve the spectral phase function Ф, which is induced by three parts： the path length difference in air L, the effective thickness of slightly dispersive cube beam splitter Teff and the nonlinear phase function due to multi-reflection of the thin film structure. We utilize the fact that the overall optical path difference （OPD） is linearly dependent on the refractive index of the beam splitter to determine both L and Teff. The spectral phase shift on reflection of thin film structure can be obtained by subtracting these two parts from Ф. We show theoretically and experimentally that our new method can provide a simple and fast solution in calculating the absolute spectral phase function of optical thin films, while still maintaining high accuracy.     

Magnetism in the single-band Hubbard model

A self-consistent spectral density approach (SDA) is applied to the Hubbard model to investigate the possibility of spontaneous ferro- and antiferromagnetism. The starting point is a two-pole ansatz for the single-electron spectral density, the free parameter of which can be interpreted as energies and spectral weights of respective quasiparticle excitations. They are determined by fitting exactly calculated spectral moments. The resulting self-energy consists of a local and a non-local part. The higher correlation functions entering the spin-dependent local part can be expressed as functionals of the single-electron spectral density. Under certain conditions for the decisive model parameters (Coulomb interaction U, Bloch bandwidth W, band occupation n, temperature T) the local part of the self-energy gives rise to a spin-dependent band shift, thus allowing for spontaneous band magnetism. As a function of temperature, second-order phase transitions are found away from half-filling, but close to half-filling, the system exhibits a tendency towards first-order transitions. The non-local self-energy part is determined by use of proper two-particle spectral densities. Its main influence concerns a (possibly spin-dependent) narrowing of the quasiparticle bands with the tendency to stabilize magnetic solutions. The non-local self-energy part disappears in the limit of infinite dimensions. We present a full evaluation of the Hubbard model in terms of quasiparticle densities of states, quasiparticle dispersions, magnetic phase diagram, critical temperatures (T_c, T_N) as well as spin and particle correlation functions. Special attention is focused on the non-locality of the electronic self-energy, for which some rigorous limiting cases are worked out.     

Anomalous magnetic splitting of the kondo resonance

The splitting of the Kondo resonance in the density of states of an Anderson impurity in a finite magnetic field is calculated from the exact Bethe-ansatz solution. The result gives an estimate of the electron spectral function for a nonzero magnetic field and the Kondo temperature, with consequences for transport experiments on quantum dots in the Kondo regime. The strong correlations of the Kondo ground state cause a significant low-temperature reduction of the peak splitting. Explicit formulas are found for the shift and broadening of the Kondo peaks. A likely cause of the problems of large- N approaches to spin- 1 / 2 impurities at finite magnetic field is suggested.     

Spin-controlled Mott-Hubbard bands in LaMnO3 probed by optical ellipsometry

Spectral ellipsometry is used to determine the dielectric function of an untwinned crystal of LaMnO3 in the range 0.5-5.6 eV at temperatures 50相似文献   

紫外臭氧垂直探测仪高精度在轨光谱定标方法研究

为监测及修正紫外臭氧垂直探测仪(SBUS)在发射以及在轨运行过程中的光谱位置的偏移,采用了一种全新的高精度在轨光谱定标方法。利用高分辨率参考光谱与仪器狭缝函数进行卷积,并将卷积结果与修正后的测量光谱进行匹配,建立了相关评价函数,计算参考光谱和测量光谱误差最小时的光谱偏移量。对于SBUS,利用此方法定标得出的光谱偏移量为0.10 nm。利用SBUS星上汞灯光谱验证了定标结果的最大误差为0.01 nm,满足仪器指标要求。实验结果证明了高精度在轨光谱定标方法的可行性及精度。     

Quark-antiquark scattering phase shift and meson spectral function in pion superfluid

We study the quark-antiquark scattering phase shift and meson spectral function in the pion superfluid described by the Nambu-Jona-Lasinio model. Meson mixing in the pion superfluid dramatically changes the full scattering phase shift and significantly broadens the spectral function of some collective modes.     

A Fiber Optic Wavelength Modulation Sensor Based on Tantalum Pentoxide Coatings for Absolute Temperature Measurements

A fiber optic low-coherence sensor based on the spectral shift of tantalum pentoxide thin films for absolute temperature sensing up to 650°C is described. A tantalum pentoxide single layer was deposited directly onto the cleaved end-face of a single mode optical fibre and was illuminated with an super luminescence diode (SLD) source through a directional coupler. Interference fringes of the film on reflection were obtained within the optical bandwidth of the SLD using an optical spectrum analyser. The spectral shift versus temperature rise showed no turning points and the output was unambiguous, linear, monotonic and gave about 0.016 nm wavelength shift in the spectrum per°C. A semi-empirical calibration procedure based on the refractive index (n) and thickness (l) of the tantalum pentoxide film for absolute thermometric measurements is described.     

碲化铅/硫化锌红外多层滤光片的光谱漂移研究

采用碲化铅和硫化锌作为镀膜材料,研制了空间红外光学系统使用的红外多层带通滤光片。本文首次利用导纳轨迹图解技术,当在空间低温条件下使用时,对由碲化铅的折射率变化引起的光谱漂移机理进行了研究。根据多层膜各膜层间存在的光学厚度的补偿效应,建立了光谱漂移模型。并对设计的滤光片采用对分法计算了它在低温条件下波长的漂移量,计算结果与研制出的滤光片实测结果吻合很好。并成功地将研究结果应用于滤光片的设计,对原设计结果进行了准确的修正,使得最终研制的滤光片在低温下完全满足使用要求。     

空气中飞秒脉冲激光器互相关信号的理论研究

利用色散脉冲传播理论和空气折射率Ciddor公式,推导了空气中飞秒脉冲激光器的互相关函数;根据互相关函数结果表达式取决于激光器光源的光谱分布,建立了在空气中不同光程路径差及环境参量变化下,不同光谱分布的飞秒脉冲激光器的脉冲之间互相关模式的数值模型.结果表明:随着传播距离的增大,互相关模型具有稳定啁啾及线性加宽;环境参量的变化只引起互相关图案的移动,并不产生任何额外线性加宽或啁啾.     

Bloch electron in a magnetic field and the ising model

The spectral determinant det(H-varepsilonI) of the Azbel-Hofstadter Hamiltonian H is related to Onsager's partition function of the 2D Ising model for any value of magnetic flux Phi = 2piP/Q through an elementary cell, where P and Q are coprime integers. The band edges of H correspond to the critical temperature of the Ising model; the spectral determinant at these (and other points defined in a certain similar way) is independent of P. A connection of the mean of Lyapunov exponents to the asymptotic (large Q) bandwidth is indicated.     

Soft x-ray resonant diffraction study of magnetic and orbital correlations in a manganite near half doping

We have utilized resonant x-ray diffraction at the Mn L(II,III) edges in order to directly compare magnetic and orbital correlations in Pr0.6Ca0.4MnO3. Comparing the widths of the magnetic and orbital diffraction peaks, we find that the magnetic correlation length exceeds that of the orbital order by nearly a factor of 2. Furthermore, we observe a large (approximately 3 eV) spectral weight shift between the magnetic and orbital resonant line shapes, which cannot be explained within the classic Goodenough picture of a charge-ordered ground state. To explain the shift, we calculate the orbital and magnetic resonant diffraction line shapes based on a relaxed charge-ordered model.     

End-to-end correlation for a C-12 hydrocarbon chain

The 19F nuclear spin-lattice relaxation rate constants were measured as a function of magnetic field strength for 1,12-diaminododecane labeled at one end with a nitroxide radical and at the other with a trifluoromethyl group. The magnetic relaxation dispersion profile (MRD) reports the spectral density function appropriate to the end-to-end correlation function for the doubly labeled molecule. After extrapolation to zero concentration to eliminate the intermolecular relaxation contribution to relaxation, the resulting intramolecular MRD profile was compared with several model approaches. The rotational model for the spectral density functions as included in the Solomon-Bloembergen-Morgan equations does not describe the data well. The earlier model of Freed for nuclear spin relaxation induced by a freely diffusing paramagnetic co-solute is not rigorous for this case because the paramagnet is tethered to the observed nuclear spin and only a restricted space in the immediate vicinity of the nuclear spin is accessible for pseudo-translational diffusion of one end of the molecule with respect to the other. A generalization of the Torrey model for magnetic relaxation by translational diffusion developed by Nevzorov and Freed, which includes the effect of restrictions imposed by the finite length of the chain, describes the experiment within experimental errors. A simple modification of the Hwang-Freed model that does not specifically include the dynamical effects of the finite tether also provides a good approximation to the data when the tether chain is sufficiently long.     

偏振光谱BRDF建模与仿真

在偏振光条件下,物体的表面反射受到折射率、表面粗糙度、入射角等多种因素的影响。针对粗糙物体表面在不同波段光照下表现出不同的偏振反射特性,提出一种基于Kirchhof理论的偏振光谱BRDF模型。利用已知材质在不同波长下的复折射率,对其折射率和消光系数部分分别反演出的对应光谱模型,进而得到复折射率的光谱模型;同借鉴经典的表面粗糙度测量方法,结合菲涅耳反射公式,推导出表面粗糙度的光谱模型,将得到的复折射率和粗糙度光谱模型与BRDF模型相结合,推导出偏振光谱BRDF建模。模型分别在折射率随波长变化、粗糙度为常量,折射率、粗糙度均随波长变化以及原模型三种情况下进行仿真对比实验,并将所得到的数据与其他资料进行对比。其结果表明,该模型能够较为准确的反映物体表面的偏振反射特性,并且能够描述偏振度随波长变化趋势的光谱特征,能够为偏振遥感、物质分类等方面的应用提供可靠依据。     

Low-loss multilayered metamaterial exhibiting a negative index of refraction at visible wavelengths

We experimentally demonstrate a low-loss multilayered metamaterial exhibiting a double-negative refractive index in the visible spectral range. To this end, we exploit a second-order magnetic resonance of the so-called fishnet structure. The low-loss nature of the employed magnetic resonance, together with the effect of the interacting adjacent layers, results in a figure of merit as high as 3.34. A wide spectral range of negative index is achieved, covering the wavelength region between 620 and 806 nm with only two different designs.     

A Green's Function Approach to the Shift of Spectral Lines in Dense Plasmas

Variations of the spectral lines in high dense ion plasmas with temperature and pressure may be characterized by the broadening as well as by the shift of spectral lines. For dense hydrogen- and alkali-plasmas (free carrier density larger than 10¹⁶/cm³) one of the possible mechanisms responsible for line profiles is considered to be the Coulomb interaction with free charged carriers. Using thermodynamic Green's functions, a systematic approach to the theory of spectral lines starting from the complex dielectric function is outlined. The line shift is derived from a perturbative treatment of the two-particle Green's function in the surrounding plasma. The shift of several lines proportional to the carrier density is evaluated as a function of the temperature and compared with experimental results.     

Peculiar Features of the Spectrum Saturation Effect When the Spectral Diffusion Operates: System with Two Frequencies

The saturation of a spectrum with two separated spectral lines is theoretically analyzed in the presence of the spectral diffusion. Surprising effects of circularly polarized alternating magnetic field on the spectrum under saturation conditions were obtained. The alternating magnetic field pushes two lines apart, while the spectral diffusion tends to shift the lines to the center of gravity. As a result, the so-called exchange narrowing of the spectrum occurs at a higher spectral diffusion rate with the increase in the amplitude of the alternating magnetic field. The spectrum is presented as a sum of two lines which correspond to the two independent collective modes of the magnetization vectors motion. The resonance frequencies of these modes depend on the spectral diffusion rate and the intensity of the alternating magnetic field.     

The impact of chirally odd condensates on the rho meson

Based on QCD sum rules we explore the consequences of a scenario for the ρ meson, where the chiral symmetry breaking condensates are set to zero whereas the chirally symmetric condensates remain at their vacuum values. This clean-cut scenario causes a lowering of the ρ spectral moment by about 120 MeV. The complementarity of mass shift and broadening is discussed. A simple parametrization of the ρ spectral function leads to a width of about 280 MeV if no shift of the peak position is assumed.     

The Spectral Shift Function and Spectral Flow

At the 1974 International Congress, I. M. Singer proposed that eta invariants and hence spectral flow should be thought of as the integral of a one form. In the intervening years this idea has lead to many interesting developments in the study of both eta invariants and spectral flow. Using ideas of [24] Singer’s proposal was brought to an advanced level in [16] where a very general formula for spectral flow as the integral of a one form was produced in the framework of noncommutative geometry. This formula can be used for computing spectral flow in a general semifinite von Neumann algebra as described and reviewed in [5]. In the present paper we take the analytic approach to spectral flow much further by giving a large family of formulae for spectral flow between a pair of unbounded self-adjoint operators D and D +  V with D having compact resolvent belonging to a general semifinite von Neumann algebra and the perturbation . In noncommutative geometry terms we remove summability hypotheses. This level of generality is made possible by introducing a new idea from [3]. There it was observed that M. G. Krein’s spectral shift function (in certain restricted cases with V trace class) computes spectral flow. The present paper extends Krein’s theory to the setting of semifinite spectral triples where D has compact resolvent belonging to and V is any bounded self-adjoint operator in . We give a definition of the spectral shift function under these hypotheses and show that it computes spectral flow. This is made possible by the understanding discovered in the present paper of the interplay between spectral shift function theory and the analytic theory of spectral flow. It is this interplay that enables us to take Singer’s idea much further to create a large class of one forms whose integrals calculate spectral flow. These advances depend critically on a new approach to the calculus of functions of non-commuting operators discovered in [3] which generalizes the double operator integral formalism of [8–10]. One surprising conclusion that follows from our results is that the Krein spectral shift function is computed, in certain circumstances, by the Atiyah-Patodi-Singer index theorem [2].