金属表面非相干线结构光条纹中心提取方法

采用线结构光法测量金属表面形貌时,由于受到金属表面光学特性和散斑噪声的影响,条纹中心的提取误差往往较大。为此,提出了一种非相干线结构光形貌测量方法,避免了散斑噪声的影响。通过分析该方法测量金属表面形貌时的条纹图像特点,提出一种适合非相干线结构光条纹的中心提取方法。该方法首先采用结合积分图像原理的自适应阈值分割算法,对原条纹图像进行分割。采用灰度重心法粗提取原条纹中心坐标,以该坐标为基准向条纹宽度方向延伸,从而确定阈值分割后条纹图的感兴趣区和背景区,并去除背景区的噪声。经中值滤波后,采用几何中心法提取条纹中心。实验结果表明：采用该方法提取粗糙度样块表面非相干光条纹中心的平均误差为1.5μm,提取齿轮渐开线样板表面非相干光条纹中心的平均误差为0.9μm,均比其线激光条纹中心的提取误差小。所提方法能实现金属表面非相干线结构光条纹中心的精确提取。     

Stripe states with spatially oscillating d-wave superconductivity in the two-dimensional t-t'-J model

We study the interplay between stripes and d-wave superconductivity in the two-dimensional t-t'-J model using a variational Monte Carlo method. The next-nearest-neighbor hopping t'<0 stabilizes the stripe states around 1/8 hole doping rate. We find that stripes and spatially oscillating superconductivity coexist depending on parameters. The superconducting orders are enhanced at the hole stripe regions. Although the energy differences are relatively small, the stripe state in which the phases between adjacent superconducting stripes are the opposite (antiphase) is also stabilized. We consider the possibility that the antiphase coexistence may explain the weakness of the c-axis Josephson couplings in the La1.6-xNd0.4SrxCuO4.     

铁磁、肖特基金属和半导体纳米自旋过滤器中的量子尺寸效应

采用转移矩阵法,研究了结构尺度对自旋过滤器中电子自旋极化特性的影响．该自旋过滤器可以通过在半导体异质结上沉积纳米尺度的铁磁条带和肖特基金属条带来实现．计算结果表明,电子的自旋极化特性强烈依赖于铁磁条带和肖特基金属条带的结构尺度和位置,即该器件中存在量子尺寸效应．此外,我们的计算结果还表明,电子的自旋极化特性还与施加在肖特基金属条上的电压所诱发的电垒高度密切相关．因此,我们可以通过改变施加在肖特基金属条上的电压来调控该器件中电子的自旋极化特性,制造一个电压可调的电子自旋过滤器．     

Colour-stripe permutation pattern for rapid structured-light range imaging

For structured-light range imaging, colour stripes can be used for increasing the number of distinguishable light patterns compared to binary black-and-white stripes. Therefore, an appropriate use of colour patterns can reduce the number of required light projections for imaging an object scene, and range imaging can be achievable in a single video frame or in “one-shot”. On the other hand, the reliability and range resolution attainable from colour stripes are generally lower than those from temporally encoded binary black-and-white patterns since colour contrast is affected by object colour reflectance and ambient light. This paper presents new methods for selecting stripe colours and designing multiple-stripe patterns for “one-shot” and “two-shot” imaging. We show that maximizing colour contrast between the stripes in one-shot imaging reduces the ambiguities resulting from coloured object surfaces and limitations in sensor/projector resolution. Moreover, a cross-stripe gradient method is presented to improve estimation of illumination patterns in one-shot imaging. Two-shot imaging adds an extra video frame and maximizes the colour contrast between the first and second video frames to diminish the ambiguities even further. Experimental results and discussion demonstrate the effectiveness and robustness of the presented one-shot and two-shot colour-stripe imaging schemes.     

Freezing of phase separation in spatiotemporal stripe patterns formed by Ag and Sb co-electrodeposition

Various spatiotemporal patterns of dark and light stripes are formed in the Ag and Sb co-electrodeposition system. In this research, we investigate the time-evolution of the stripe width of a spatiotemporal stripe pattern with a size of ca. 10 μm. The results show that the stripe width increases with time and is eventually saturated. Such a phenomenon is predicted by some theories of spinodal decomposition of materials with chemical reactions in a nonequilibrium system. This suggests that the pattern is formed by the spinodal decomposition of metal alloys, Ag and Sb, with chemical reactions in a nonequilibrium system, which has not yet been reported in a metallic system.     

Stripes and superconductivity in cuprates

Holes doped into the CuO₂ planes of cuprate parent compounds frustrate the antiferromagnetic order. The development of spin and charge stripes provides a compromise between the competing magnetic and kinetic energies. Static stripe order has been observed only in certain particular compounds, but there are signatures which suggest that dynamic stripe correlations are common in the cuprates. Though stripe order is bad for superconducting phase coherence, stripes are compatible with strong pairing. Ironically, magnetic-field-induced stripe order appears to enhance the stability of superconducting order within the planes.     

变条长实验测量GaN增益时条宽的影响

研究了光学变条长实验中条的宽度对半导体激光器光增益测量的影响,提出利用光刻溅射处理样品来严格控制泵浦条的宽度,并详细研究了泵浦条宽度与样品增益及饱和长度关系。实验表明:泵浦条宽度越窄,饱和长度越长,但测得的增益系数有所减小。本文利用非平衡载流子扩散模型对此现象进行了解释。     

Investigation of magnetically coupled ferromagnetic stripe arrays

We studied the magnetic coupling of ferromagnetic, submicron-sized stripes in the material system MnAs on GaAs. A specific coupling state, determined by stripe period and stripe width, can be tuned via film thickness and temperature, respectively. Micromagnetic imaging – in combination with micromagnetic simulations – reveals two coupling regimes. Strong magnetic coupling between the stripes creates micromagnetic domains extending across several stripes, whereas weak coupling allows for demagnetization within individual stripes. This behavior is observed for all investigatedfilm thicknesses, since a stripe geometry leading to a given coupling scenario is a function of temperature. PACS 68.37.Rt; 68.35.Rh; 75.70.-i; 75.70.Kw     

Complete-single-mode operation of 180° mode phased array lasers by improving temperature distribution inside the stripe region

180° mode phased array lasers with multiple stripes were systematically investigated for high-power, single lateral mode operation. Phased array lasers with a conventional loss guide structure were fabricated for 180° mode operation because the structure allowed the threshold gain of 180° mode to become smallest by introducing optical loss between stripes and outside the stripe region. It showed complete single lateral mode operation under pulsed condition. However, under continuous wave operation, phase-uncoupling occurred at the edge emitters as a result of the temperature distribution inside the stripe region. This was confirmed both experimentally and theoretically. To minimise the temperature distribution, dummy stripes were introduced outside the stripe region. The current in the dummy stripes did not cause lasing, but did increase the temperature of the edge stripes, which improved the thermal distribution inside the stripe region. As a result, complete single lateral 180° mode operation under continuous wave operation was attained.     

光致异构聚合物材料中暗条纹的Y型分裂研究

数值分析方法研究了对称轴两侧光场具有相位跃变的暗条纹在具有光致异构非线性的聚合物中的演化情况及一些有关性质.结果表明，两侧光场相位跃变不为π时，入射暗条纹会向两边分开而形成Y型分裂；相位跃变从0到π增大，分裂程度变小.发现相位超前一边分出来的灰条纹与原传播方向之间的夹角对于不同相位跃变值基本保持不变，而相位滞后一边分出来的灰条纹与原传播方向之间的夹角则随相位跃变的增大而减小；相同相位跃变、不同光强的光束分开角度基本保持不变.数值模拟发现这种Y型分裂在材料中产生的折射率改变具有波导作用，可以使入射高斯光束产生Y型分裂. 关键词： 光伏空间孤子 光致异构 Y型分裂 分步傅里叶法     

Photoemission signatures of valence-bond stripes in cuprates: Long-range vs. short-range order

Recent experiments indicate that the tendency toward the formation of unidirectional charge density waves (“stripes”) is common to various underdoped cuprates. We discuss momentum-resolved spectral properties of valence-bond stripes, comparing the situations of ideal and short-range stripe order, the latter being relevant for weak and/or disorder-pinned stripes. We find clear signatures of ordered stripes, although matrix element effects suppress most shadow band features. With decreasing stripe correlation length, stripe signatures are quickly washed out, the only remaining effect being a broadening of antinodal quasiparticles. This insensitivity of photoemission to short-range stripe order may be employed to distinguish it from nematic order, e.g. in underdoped YBa₂Cu₃O_6+δ.     

Antiferromagnetic spin ladders effectively coupled by one-dimensional electron liquids

We study a model of the stripe state in strongly correlated systems consisting of an array of antiferromagnetic spin ladders, each with n(leg) legs, coupled to each other through the spin-exchange interaction to charged stripes in between each pair of ladders. The charged stripes are assumed to be Luttinger liquids in a spin-gap regime. An effective interaction for a pair of neighboring ladders is calculated by integrating out the gapped spin degrees of freedom in the charged stripes. The low energy effective theory of each ladder is a nonlinear sigma model with additional cross couplings of neighboring ladders, which favor either in-phase or antiphase short-range spin orderings depending on the physical parameters of the charged stripe.     

Critical fluctuations and quenched disordered two-dimensional charge stripes in La(5/3)Sr(1/3)NiO4

Using high-resolution x-ray scattering, we have demonstrated the existence of quenched disordered charge stripes in a single crystal of La (5/3)Sr (1/3)NiO (4) at low temperatures. Above the second-order transition critical scattering was observed due to fluctuations into the charge stripe phase. The charge stripes are shown to be two dimensional in nature both by measurements of their correlation lengths (xi(a) approximately 185 A, xi(b) = 400 A, and xi(c) approximately 25 A) and by the critical exponents of the charge strip transition. The charge stripe ordering did not develop long-range order even at low temperatures, indicating that the charge stripes are disordered and that the length scale of the disorder is quenched.     

Stripes on a 6-leg Hubbard ladder

While density matrix renormalization group calculations find stripes on doped n-leg t-J ladders, little is known about the possible formation of stripes on n-leg Hubbard ladders. Here we report results for a 7x6 Hubbard model with four holes. We find that a stripe forms for values of U/t ranging from 6 to 20. For U/t approximately 3-4, the system exhibits the domain wall feature of a stripe, but the hole density is very broadened.     

基于数字彩色结构光投影的唇动三维测量

提出了基于数字彩色结构光投影的动态三维测量轮廓术,用于人在讲话过程中嘴唇的三维测量。介绍了彩色编码轮廓术的基本原理,再通过分色和条纹细化处理,实现了对动态不连续嘴唇的测量。实验验证了测量方案的有效性。     

Late stage, non-equilibrium dynamics in the dipolar Ising model

Magnetic domain structures are a fascinating area of study with interest deriving both from technological applications and fundamental scientific questions. The nature of the striped magnetic phases observed in ultra-thin films is one such intriguing system. The non-equilibrium dynamics of such systems as they evolve toward equilibrium has only recently become an area of interest and previous work on model systems showed evidence of complex, slow dynamics with glass-like properties as the stripes order mesoscopically. To aid in the characterization of the observed phases and the nature of the transitions observed in model systems we have developed an efficient method for identifying clusters or domains in the spin system, where the clusters are based on the stripe orientation. Thus we are able to track the growth and decay of such clusters of stripes in a Monte Carlo simulation and observe directly the nature of the slow dynamics. We have applied this method to consider the growth and decay of ordered domains after a quench from a saturated magnetic state to temperatures near and well below the critical temperature in the 2D dipolar Ising model. We discuss our method of identifying stripe domains or clusters of stripes within this model and present the results of our investigations.     

Experimental investigation of plasma excitations in asymmetric stripes of two-dimensional electrons

The plasmon microwave response of symmetric and asymmetric stripes of two-dimensional electrons with different boundary conditions has been studied. The symmetric case corresponds to stripes either without ohmic contacts or with ohmic contacts on both sides, while the contact in asymmetric stripes is present only on one side. It has been shown that there is a frequency shift of the observed plasma modes in asymmetric stripes. The lowest-frequency mode becomes a previously unobserved mode for which the quarter wavelength of the plasmon coincides with the length of the stripe. The behavior of the lowest mode and its multiple frequencies in asymmetric stripes has been studied under variation of the magnetic field, electron density, and temperature and size of the stripes. The results indicate that all plasma modes in symmetric and asymmetric stripes have the same physical nature.     

推扫型干涉成像光谱仪去除条带非均匀性的方法

分析了推扫型干涉成像光谱仪的结构特点和工作原理,指出了由于加工误差导致入射狭缝的宽度不均匀,使干涉图像沿狭缝方向存在亮度差异,复原后的光谱立方体图像上出现平行于推扫方向的非均匀性条带,影响了光谱立方体的图像质量和光谱精确度.采取校正系数法去除条带,讨论了获取校正系数的方法,并使用仪器的定标干涉数据提取成像面上沿狭缝方向的不均匀特性,获得了校正系数,对干涉图像进行处理以消除条带.结果表明:校正系数法能够去除大部分条带.根据处理后残余条带的情况,在没有在轨定标数据的情况下,使用均匀景物的光谱立方体数据提取不均匀特性,修改了校正系数,有效地消除了残余条带.     

Size- and voltage-dependent spin polarization in hybrid ferromagnetic-Schottky-metal and semiconductor nanostructure

Recently, an electron-spin filter was proposed by depositing two nanosized ferromagnetic metal stripe and Schottky normal metal stripe on the top of the semiconductor heterostructure [F. Zhai, H.Q. Xu, Y.Guo, Phys. Rev. B 70 (2004) 085308]. In this paper, we theoretically investigate the effect of device parameters on electron-spin polarization in the spin filter. It is shown that the electron-spin polarization is dependent greatly on the sizes and the position of the stripes. Thus, a quantum size effect exists in this device and the optimal spin polarization can be achieved by felicitously fabricating the stripes. It also is shown that the spin polarization can be altered by adjusting the electric-barrier height induced by an applied voltage to the Schottky metal stripe, which can result in a voltage-tunable electron-spin filter.     

Stripe patterns in degenerate optical parametric oscillators

We experimentally demonstrate the stripe (or roll) patterns in a broad-aperture degenerate optical parametric oscillator in a plane-mirror minicavity. The stabilization of stripes is achieved by seed injection at a subharmonic frequency. We measure the temporal spectra of the stripe pattern and obtain the 1/f-like noise spectra.