Effect of turbulent atmosphere on the on-axis average intensity of Pearcey–Gaussian beam

The propagation characteristics of the Pearcey–Gaussian(PG) beam in turbulent atmosphere are investigated in this paper.The Pearcey beam is a new kind of paraxial beam,based on the Pearcey function of catastrophe theory,which describes diffraction about a cusp caustic.By using the extended Huygens–Fresnel integral formula in the paraxial approximation and the Rytov theory,an analytical expression of axial intensity for the considered beam family is derived.Some numerical results for PG beam propagating in atmospheric turbulence are given by studying the influences of some factors,including incident beam parameters and turbulence strengths.     

多艾里光束合成自聚焦光束的实验实现

多光束合成和单光束聚焦一直是提高激光束功率和功率密度的两个重要方法. 结合艾里光束在自由空间中沿弯曲路径传播的特性, 从数值模拟和实验两个方面, 研究了利用多个一维艾里光束合成自由空间自聚焦光束的方法, 并对所得到的模拟和实验结果进行了对比. 采用分步束传播法, 分别模拟了由四个和八个一维艾里光束合成的自聚焦光束在自由空间中的传播过程, 给出了自聚焦光束在传播过程中横向和纵向的光强分布和变化趋势. 采用计算全息和空间光调制器技术实验, 实现了多个一维艾里光束合成的自聚焦光束. 实验中分别测量了四个和八个一维艾里光束合成的自聚焦光束的横向光强分布. 实验结果和理论结果符合得较好. 另外, 为了进一步增大自聚焦光束的功率, 可以增加参与合成的一维艾里光束的数量. 同时, 自聚焦光束的焦距可以通过调整各个一维艾里光束的相对位置进行调节.     

A Rotationally Symmetric Multifocal Pearcey Beam with a Polygonal Profile

The polygonal multifocal propagation properties and particle trapping experiments of a new kind of power-exponential-phase vortex chirped circular Pearcey Gaussian beam are investigated. Theoretical and experimental results show that it is possible to adjust the position and transverse spatial distribution of the beam in focal plane, as well as to make the transverse intensity distribution emerge an arbitrary polygonal profile by changing the distribution factor and vortex topological charge. Stable trapping of multiple particles is achieved in the experiment with transverse intensity fields in the polygon plane with different topological charges.     

双Pearcey光束的构建及数学机理研究

通过推导椭圆线的菲涅耳衍射分布,得到了形如Pearcey函数的数学表达式.通过数值模拟和实验产生,发现椭圆光环经菲涅耳衍射后形成的Pearcey光束外形上很像两个经典Pearcey光束面对面组合而成,我们把它命名为双Pearcey光束,这是形式不变Pearcey光束家族的新成员.随后,利用数学突变理论,给出了双Pearcey光束所具有的光学拓扑结构的数学机理和相应表达式.     

The Pearcey Process

The extended Airy kernel describes the space-time correlation functions for the Airy process, which is the limiting process for a polynuclear growth model. The Airy functions themselves are given by integrals in which the exponents have a cubic singularity, arising from the coalescence of two saddle points in an asymptotic analysis. Pearcey functions are given by integrals in which the exponents have a quartic singularity, arising from the coalescence of three saddle points. A corresponding Pearcey kernel appears in a random matrix model and a Brownian motion model for a fixed time. This paper derives an extended Pearcey kernel by scaling the Brownian motion model at several times, and a system of partial differential equations whose solution determines associated distribution functions. We expect there to be a limiting nonstationary process consisting of infinitely many paths, which we call the Pearcey process, whose space-time correlation functions are expressible in terms of this extended kernel.     

Pearcey光束簇的实验产生和光学结构研究

基于微分几何理论和衍射光学理论, 给出了决定Pearcey光束光学结构的因素. 通过数值模拟和实验, 理论构造并实际产生了一簇光学拓扑结构不同的Pearcey光束. 随后, 它们的基本光学性质被研究. 研究结果表明, Pearcey光束的结构灵活可控, 因而有望在科学实验中发挥新的作用.     

Differential Raman scattering from impurity soft modes in mixed crystals of K1−xNaxTaO3 and K1−xLixTaO3

Impurity modes are observed in crystals of KTaO₃ doped with Na and Li, using differential Raman spectroscopy. One of the modes is shown to soften as the temperature approaches the ferroelectric transition temperature. Analysis of the results shows that the Na and Li ions do not occupy center of inversion positions. The roll of this observation in the inducement of ferroelectricity in these crystals is briefly discussed.     

Glasslike thermal conductivity of tourmaline at low temperatures

Thermal conductivity measurements parallel and perpendicular to the c-axis in tourmaline single crystals are reported in the range of 1.7 – 35K. The spontaneous polarization is constrained to the c-axis in tourmaline. The thermal conductivity (K) follows the glasslike K ∝ T^1.9 below 6K in both crystallographic directions, and the magnitude of K is in the upper range found in glasses. It is concluded that the glasslike thermal properties associated with the spontaneous polarization in ferroelectric - type solids occur isotropically throughout the crystal and are not limited to the polarization direction.     

Detection of parametric X-ray radiation from moderately relativistic protons in crystals

The spectral maxima of parametric x-ray radiation that are emitted by moderately relativistic protons interacting with various crystals have been detected. The spectral positions of these maxima depend on the crystal orientation angle and they are consistent with the theoretical values. The measurements were carried out with silicon and graphite crystals on the 5-GeV proton beam extracted from the Nuclotron at the Laboratory of High Energies, JINR.     

Transmission electron microscopy of GaN columnar nanostructures grown by molecular beam epitaxy

The GaN columnar crystals of nanometric sizes have been grown by molecular beam epitaxy with high-frequency plasma initiation of nitrogen discharge. The types and distribution of defects in these nanostructures on the (0001) sapphire substrates are studied by transmission electron microscopy (TEM). It is revealed that inversion domains begin to form almost at the interface irrespective of the presence of an initial low-temperature buffer layer. The critical diameter of dislocation-free columns, their density, and mean sizes are determined. It is shown that the low-temperature buffer layer affects the density of dislocations, their spatial distribution, and the mean sizes of columns. The nanosizes of grown crystals suggest a further use of these crystals and the growth method for producing molecular-beam epitaxial quantum-size objects (quantum dots and wires) in a promising AlGaInN system.     

Are you centered? An automatic crystal‐centering method for high‐throughput macromolecular crystallography

Crystal centering is a key step in macromolecular X‐ray crystallography experiments. A new method using image‐processing and machine‐vision techniques allows the centering of small crystals in the X‐ray beam. This method positions crystals even when the loop is initially out of the camera's field of view and adapts to the difficulty of the experiment. The process has been tested on many diverse crystals with a 93% success rate when compared with manual centering.     

Dynamic Optical Vortex Trajectory Guided by the Symmetric Pearcey Gaussian Vortex Beam in the Uniformly Moving Parabolic Potential

This paper analytically and numerically proposes the propagation dynamics of the symmetric Pearcey Gaussian vortex beam (SPGVB) in the uniformly moving parabolic potential. The optical vortex located in the initial plane produces a vortex channel in the presence of the uniformly moving parabolic potential, called the vortex trajectory. The vortex trajectory can be manipulated dynamically by configuring different combinations of the parameters, and the optical intensity and the focal position can also be affected. Moreover, the spatial dynamic vortex trajectory is derived analytically, and the 2D on-axis and off-axis vortex scenarios are also presented. Our work expands the methods of the vortex trajectory manipulation and may broaden more practical potential applications in the particle manipulation.     

DNA microarray scanner with a DVD pick-up head

A low-cost highly sensitive DNA microarray scanner for fluorescent detection is developed based on the pick-up head of a commercially available optical storage device, DVD. A laser beam of 650 nm, generated by a DVD laser diode, is used for dynamic auto-focusing as well as the excitation of Cy5 fluorescent dye. The fluorescence intensity emitted from Cy5 dye is measured by a photomultiplier tube (PMT). In contrast to other microarray scanners, the DVD-based scanner offers the auto-focusing function using the focus error signal (FES) and a voice coil motor (VCM), and this enables fast response, high accuracy and compact size. The fluorescence-detecting performance of the scanner is inspected by using a commercial BAC (bacterial artificial chromosome) oligonucleotide chip and a scanner evaluation microarray (DS01). Experiments have shown that the DVD-based scanner meets the limit of detection, ensuring the feasibility of a low-cost, highly sensitive DNA microarray scanner.     

Symmetric Swallowtail Beams in the Rectangle Frame

A new type of symmetric swallowtail beam (SSB) in the rectangle frame is introduced here. These kinds of beams are highly tunable with multiple manipulation parameters. The focal length and the focus intensity can be controlled precisely. The SSBs can guide the off-axis vortex to their center. And the experimental results agree well with the numerical simulations. Besides, stable trapping of particles by utilizing the SSBs' auto-focusing property and rectangle symmetry is also observed.     

Impurity Luminescence of Alexandrite Crystals

The luminescence of alexandrite excited by a highcurrent electron beam is investigated. Its spectrum has bands of the impurity ions Cr³⁺ and of the Cr–Cr pairs and also the band at = 492–495 nm. In all of the crystals we have detected chromium ions distributed over two nonequivalent positions, differently in different crystals. It is shown that the color of the crystals and its change on illumination of the crystals with the light of different spectral composition depend mainly on the chromium ions and their distribution over crystalline positions. A noticeable effect of other impurity ions is noted for a number of crystals.     

Mutually Pumped Phase Conjugation of Three Incoherent Beams with a Novel Photorefractive Crystal

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航空成像系统检调焦技术分析与展望

介绍了航空成像系统的特殊工作环境及应用需求对检调焦技术的要求,讨论了当前3种主要检调焦方法：程序标定法,光学自准直法及图像对比度法,总结并比较了3种方法的检调焦精度、检调焦时间等性能指标。最后着重讨论了基于光场成像理论与光学系统离焦深度之间的关系,对基于光场成像原理的快速检调焦技术进行了深入的分析、讨论,并对该技术在航空成像系统的应用前景进行了展望分析。     

Universality for the Pearcey process

Consider non-intersecting Brownian motions on the line leaving from the origin and forced to two arbitrary points. Letting the number of Brownian particles tend to infinity, and upon rescaling, there is a point of bifurcation, where the support of the density of particles goes from one interval to two intervals. In this paper, we show that at that very point of bifurcation a cusp appears, near which the Brownian paths fluctuate like the Pearcey process. This is a universality result within this class of problems. Tracy and Widom obtained such a result in the symmetric case, when the two target points are symmetric with regard to the origin. This asymmetry enabled us to improve considerably a result concerning the non-linear partial differential equations governing the transition probabilities for the Pearcey process, obtained by Adler and van Moerbeke.     

Inversion domain boundaries in ZnO with additions of Fe2O3 studied by high-resolution ADF imaging

Columns of metal atoms in the polytypoid compound Fe2O3(ZnO)15 could be resolved by high angle annular dark field imaging in a transmission electron microscopy (TEM)/STEM electron microscope--a result which could not be realized by high-resolution bright field imaging due to inherent strain from inversion domains and inversion domain boundaries (IDBs) in the crystals. The basal plane IDB was imaged in [11 00] yielding the spacing of the two adjacent ZnO domains, while imaging in [21 1 0] yields the position of single metal ions. The images allow the construction of the entire domain structure including the stacking sequence and positions of the oxygen ions. The IDB consists of a single layer of octahedrally co-ordinated Fe3+ ions, and the inverted ZnO domains are related by point symmetry at the iron position. The FeO6 octahedrons are compressed along the ZnO c-axis resulting in a FeO bond length of 0.208 nm which is in the range of FeO distances in iron containing oxides. The model of the basal plane boundary resembles that of the IDB in polytypoid ZnO-In2O3 compounds.     

基于红外图像边缘特性的自动对焦技术

与可见光图像相比,红外图像的分辨率较低,景物边缘较为粗糙,传统的自动调焦技术无法直接用于红外热成像系统。为了解决这一问题,采用基于红外图像边缘特性的自动对焦算法,建立快速有效的对焦评价函数,驱动高精度光机闭环控制单元,以实现快速、准确的红外自动对焦。系统包含数字处理单元和运动控制单元。其中数字图像处理单元主要进行红外数字图像的采集,利用Roberts梯度算子提取红外图像中的信息量,并统计边缘点数以评价图像的清晰度,实时计算序列红外图像中细节和信息量的变化量和趋势,从而提供运动控制单元所需的位置给定。运动控制单元则主要进行调焦电机的控制及驱动,完成自动聚焦的过程控制。最后,通过实验证明了该方案的有效性。