固体棒状热容激光器的热分析

 计算出固体棒状热容激光器在不同散热边界条件下的温度分布和随时间的演变，与实验测量的结果进行了对比。计算结果表明：激光器工作在热容模式时，不同散热边界条件下激光介质内的温度分布在激光发射期间区别不大，激光发射期间，激光介质内的温度分布主要取决于泵浦光的吸收。但是散热过程中的不同散热边界条件下温度分布演化大不相同，此时的温度分布主要取决于散热边界条件。     

Fiber spin-profile designs for producing fibers with low polarization mode dispersion

Using coupled-mode theory, we develop a theoretical model to analyze the effects of fiber spin profiles on polarization mode dispersion (PMD). Constant, sinusoidal, and frequency-modulated spin profiles are examined, and phase-matching conditions are analyzed. Our analysis shows that PMD can be reduced effectively by use of frequency-modulated spin profiles.     

Calculations of track parameters and plots of track openings and wall profiles in CR39 detector

Computer programs have been developed to calculate track parameters and to plot track openings and wall profiles. The programs are based on equations derived for three-dimensional consideration of track development. All possible cases of track openings and wall profiles are obtainable from these equations. Results are given for lengths of major and minor axes, track depths and surface areas of track openings. Some examples of track openings and wall profiles are also presented.     

Cu-4wt%Ti合金有序化X射线与电子衍射谱的计算机模拟

在点阵波理论基础上,通过假定Cu-4wt%Ti合金中溶质原子浓度的适当分布并建立与之相应的衍射波波幅表达式,利用计算机模拟得该合金调幅分解与有序化共存时X射线衍射边带形貌,其波形与实验结果颇为相近;进一步根据波的叠加原理在两相互垂直方向上对上述衍射形貌合成,获得Cu-4wt%Ti合金400℃时效较长时间同时出现的D1a型和B2型复杂有序化超点阵斑,其强度与位置分布均与透射电镜(TEM)衍射谱完全一致. 关键词：     

Diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles by a volume holographic grating

In this paper, the diffraction properties of an ultrashort optical pulse with arbitrary profiles in time diffracted by a volume holographic grating are investigated using the modified Kogelnik coupled-wave theory. Simple analytical expressions for the spectrum and spatial profiles of the transmitted and diffracted beams are obtained. The dependences of the diffraction bandwidth, the Bragg selectivity bandwidth and the total diffraction efficiency of the volume grating on the temporal profiles of the input ultrashort pulse are investigated. For three different temporal profiles, numerical results of diffraction properties are given. It is shown that the temporal shapes of the input pulsed beams have been found to be an important factor in the analyses of the propagation characteristics.     

Residual stress profiles in optical fibers determined by the two-waveplate-compensator method

Stress-induced birefringence impacts the performance of many optical devices. Techniques are needed to measure accurately stress profiles in optical fibers. The two-waveplate-compensator (TWC) method allows the accurate measurement of small retardations. The full-field TWC method is applied here to measure the two-dimensional retardation distribution of single-mode fibers with a spatial resolution of 0.45 μm and a sensitivity of 0.07 nm. Axial stress profiles are hence determined along the axis of the fiber. The stress profiles determined with the TWC method are in good agreement with profiles previously reported in the literature while containing less noise and resolving more details.     

Analysis and design of grating couplers

Based on an accurate perturbation analysis of the guiding properties of dielectric gratings, simple design criteria are developed for grating couplers which transfer the energy of a beam into or out of an optical waveguide. Gratings having arbitrary groove shapes are considered and explicit formulae are given for the leakage parameters of gratings with symmetric profiles. The results cover TE_v and TM_v modes and they apply to both shallow and deep grating grooves. The variation of the leakage parameter α in rectangular gratings is examined in detail; these rectangular gratings are then used as basic configurations for predicting the characteristics of other grating profiles. Particular attention is given to trapezoidal and triangular profiles and gratings with asymmetric profiles are also discussed.     

Measurements of the space potential of electron cyclotron heatedplasmas in the Advanced Toroidal Facility

A heavy ion beam probe has been used to measure the space potential of electron cyclotron heated plasmas in the Advanced Toroidal Facility. The results of the measured potential profiles are presented along with the radial electric field strength profiles derived from these measurements. The measured potential profiles have been compared to those predicted by a simple model of the plasma based upon an ambipolarity constraint on the ion and electron particle fluxes in steady state. The trends of the measured and modeled profiles are in agreement, although the strength of the electric field predicted by the model is much greater than that inferred from the potential profile measurement. When an oxygen-like impurity ion species is added to the model, the predicted electric field strengths are altered significantly and become much closer to the measured values     

Acoustic measurements of boundary layer flow and sediment flux

Results are reported on an assessment of the application of coherent Doppler and cross-correlation techniques to measure nearbed boundary layer flow. The approaches use acoustic backscattering from sediments entrained into the water column from the bed, to obtain high-resolution profiles of the nearbed hydrodynamics. Measurements are presented from a wave tunnel experiment in which sediment was entrained by unidirectional, oscillatory, and combined flows. The data collected have been used to evaluate the capability of the two flow techniques to measure boundary layer mean, turbulent, and intrawave velocity profiles. Further, the backscattered signal has been used to measure suspended sediment concentration profiles, which have been combined with the velocity profiles to obtain high-resolution measurements of boundary layer sediment flux.     

Correction of temperature influence on the wind retrieval from a mobile Rayleigh Doppler lidar

A mobile Rayleigh Doppler lidar based on double-edge technique is implemented for simultaneously observing wind and temperature at heights of 15 km-60 km away from ground.Before the inversion of the Doppler shift due to wind,the Rayleigh response function should be calculated,which is a convolution of the laser spectrum,Rayleigh backscattering function,and the transmission function of the Fabry-Perot interferometer used as the frequency discriminator in the lidar.An analysis of the influence of the temperature on the accuracy of the Une-of-sight winds shows that real-time temperature profiles are needed because the bandwidth of the Rayleigh backscattering function is temperature-dependent.An integration method is employed in the inversion of the temperature,where the convergence of this method and the high signal-to-noise ratio below 60 km ensure the accuracy and precision of the temperature profiles inverted.Then,real-time and on-site temperature profiles are applied to correct the wind instead of using temperature profiles from a numerical prediction system or atmosphere model.The corrected wind profiles show satisfactory agreement with the wind profiles acquired from radiosondes,proving the reliability of the method.     

Combined experimental and computational study of laminar, axisymmetric hydrogen–air diffusion flames

We investigate the structure of two-dimensional, axisymmetric, laminar hydrogen–air flames in which a cylindrical fuel stream is surrounded by coflowing air, using laser-diagnostic and computational methods. Spontaneous Raman scattering and coherent anti-Stokes Raman scattering (CARS) are used to measure the distributions of major species and temperature. Computationally, we solve the governing conservation equations for mass, momentum, energy, and species, using detailed chemistry and transport. The fuel is diluted with nitrogen (1:1) to reduce heat transfer to the burner, to match the zero temperature gradient at the fuel exit. Three average fuel exit velocities are studied: 18, 27, and 50 cm/s. Comparisons of the measured and computed results are performed for radial profiles at a number of axial positions, and along the axial centerline. Peak major species mole fractions and temperatures are quantitatively predicted by the computations, and the axial species profiles are predicted to within the experimental uncertainty. In the radial profiles studied, base-case computations excluding thermal diffusion of light species were in excellent agreement with the measurements. While the addition of thermal diffusion led to some discrepancy with the measured results, the magnitude of the differences was no more than 25%. The computations predicted the axial centerline profiles from the burner exit to the maximum temperature well, though the experimental temperatures in the downstream mixing region decreased somewhat faster than the computed profiles. Radiative losses are seen to be negligible in these flames, and changes in transport properties and variations in initial flow velocities generally led to only modest changes in the axial profiles. The results also show that the detailed axial profiles of major species and temperature at different fuel jet velocities scale quantitatively with the jet velocity.     

Refractive index changes induced by sheet beams with various intensity distributions in LiNbO<Subscript>3</Subscript>:Fe crystal

1 IntroductionSince the discovery of photorefractive effect by Ashkin et al. at the Bell laboratories in 1966[1], such effects of light-induced refractive index changes in electro-optic oxide crystals have attracted great attention because of their potential use in volume holo- graphic storage[2], optical information processing[3], optical spatial solitons[4], and light-induced optical waveguides[5―9]. The photo-induced index changes are the basis ofthe entire photorefractive phenomena in pho…     

Density profiles in tokamaks from electron cyclotron radiation spectra

Measurement of the line shape of optically thick and optically thin lines in the electron cyclotron radiation spectrum emitted by a tokamak plasma may yield both electron temperature and density profiles. Currently temperature profiles are routinely extracted from optically thick lines. Consequently, this paper is addressed to the density profile problem. Algorithms for extracting density profiles are outlined in the case of uncontrolled reflection and controlled reflection of the cyclotron radiation within the tokamak vacuum chamber.     

On the possible role of the bootstrap effect in the RF current drive experiments

Conditions of existence of the bootstrap effect at anomalous diffusion in tokamaks are discussed. Assuming that these conditions are fulfilled at lower hybrid current drive, various models of anomalous diffusion and of temperature profiles are considered. Toroidal current density profiles and related quantities are calculated, demonstrating strong dependences on the electron temperature profiles and on the effective ion charge Z_eff. Recommendations for experimental revealing the bootstrap current are presented.     

Real structure effects in X-ray waveguide optics: The influence of interfacial roughness and refractive index profile on the near-field and far-field distribution

We generalize the optical treatment of X-ray waveguides to index profiles of arbitrary shape. The modes of the waveguides are computed numerically by Numerov’s method. The method is first validated by considering profiles for which analytical solutions exist. Next, the effects of different shape functions and of interfacial roughness on the near and far-field intensity distributions are studied. The results are helpful to judge the real structure effects, e.g. resulting from fabrication imperfections, on the optical performance, as well as to optimize optical properties by designing generalized index profiles.     

Molecular Compton profiles from SCF-MO wavefunctions

Compton profiles are derived from ab initio SCF-MO wavefunctions calculated for cyclopropane, propene, aziridine, ethanimine, ethenamine, oxirane, acetaldehyde and formamide using Dunning's gaussian orbital basis. Good agreement with the experimental profile is found for formamide. The differences between the profiles for the cyclic and acyclic isomers are only slightly larger than the experimental accuracy that can presently be achieved. The cyclic compounds have slightly broader profiles and there are no significant differences arising from strain. Comparison with profiles derived from localized orbital contributions indicate that the localized orbital approach is essentially valid for these systems.     

Theoretical and experimental analyses of recording mark microstructures in signal waveform modulation optical disc

In this paper,we propose a dynamic mastering process model for signal waveform modulation (SWM) optical disc.To form the ideal microstructures and solve the problems in the SWM master manufacturing process,we use this model to simulate the three-dimensional mark profiles in the SWM read-only disc.The simulated micro-patterns of recording pits and lands are employed to optimize the writing strategy and provide a quantitative basis for manufacturing the sub-pits and sub-lands.The simulation mark profiles are compared with the experimental ones,which are produced with the optimized writing strategy parameters.Comparison results demonstrate that the simulated profiles are highly consistent with the actual ones.     

Thorpe尺度估算库尔勒、茂名、拉萨大气光学湍流廓线

在新疆库尔勒、广东茂名海边、西藏拉萨三个地区释放的探空气球, 实现了温度、气压、风速等常规气象参数以及大气折射率结构常数的廓线测量。基于Tatarski湍流参数化方案以及以上地区探空数据, 利用Thorpe尺度估算了新疆库尔勒、广东茂名海边、西藏拉萨三个地区的高空大气光学湍流廓线, 并将这三个地区实测的廓线与其对应的估算结果做了对比, 结果表明: 估算值与实测值在量级和变化趋势上表现出较好的一致性, 相关性分别为69%, 60%, 68%;Thorpe尺度相较于其他估算湍流廓线的参数化方法输入参数少、更简便。     

Correction of self-absorption spectral line and ratios of transition probabilities for homogeneous and LTE plasma

Expressions for fundamental spectral line parameters are reported for Gaussian and Lorentzian shape profiles for homogeneous plasma at equilibrium in presence of the self-absorption. These expressions for Lorentzian profiles are applied to the determination of the ratios of transition probabilities and the ratios of optical thicknesses by a new method that we propose in this article. The self-absorption is computed by spectral line profiles with a Simplex algorithm program fitting. Applications to some experimental lines illustrate the appropriate corrections.     

Polarized velocity selective spectroscopy of atomic rubidium using counterpropagating beams

A scheme to obtain dispersion-like profiles using polarized velocity selective spectroscopy is presented. A circularly polarized pump laser beam whose frequency is scanned, and a linearly polarized, probe beam locked to a resonant frequency in the atom cross at a rubidium absorption cell. The transmitted intensities of the probe beam, with mutually perpendicular polarization directions are detected as the frequency of the pump beam is scanned. The sum of these two signals gives absorption profiles, while the difference results in dispersion profiles. This scheme is tested in the D₂ manifold of atomic rubidium. Weaker cross-over lines are found to be present and the slopes of their dispersion profiles are found to be opposite to those of the atomic transitions. This allowed an unambiguous determination of the atomic lines in both ⁸⁵Rb and ⁸⁷Rb, something that is particularly useful for the identification of the repumping transition in neutral atom trapping experiments. The dispersion profiles obtained are also suitable for frequency locking to atomic transitions or cross-over lines in both isotopes.