Self-guided operation of singly resonant continuous-wave optical parametric oscillator based on bulk MgO-doped PPLN

We report on a self-guided operation of a green-pumped singly resonant continuous-wave optical parametric oscillator with a bulk MgO-doped PPLN crystal. It is achieved by increasing the OPO cavity length beyond the stability boundary so that the OPO can only oscillate with formation of a thermally induced waveguide inside the crystal. The effects of the thermal waveguide on the OPO performance are studied by measuring output power characteristics at different cavity lengths. Improvement of spatial mode quality and stability of output power by self-guiding is demonstrated. Measurement of temporal characteristics proves that formation of the waveguide originates from the photo-thermal effect in the nonlinear crystal by absorption of pump power.     

On the problem of the formation of an open sector instead of a twin boundary in electrolytic pentagonal small particles

The experimental proof of the possibility of the formation of an open sector instead of a twin boundary in pentagonal small particles, which was previously regarded in the literature as an improbable channel of relaxation of the elastic stress associated with a disclination defect, is presented. The relation between the critical size of the pentagonal small particle and the sector angle at which the probability of this channel of elastic stress relaxation becomes considerable is discussed.     

Numerical analysis of pulse formation in solid-state lasers mode-locked with a linear external cavity

We analyse pulse formation in solid-state lasers mode-locked with a linear external cavity with translating mirror. Based on a numerical simulation the mode-locking mechanism is found to be that of an active mode-locking due to the explicitly time-dependent phase shift by the external cavity involving a slowly moving mirror and a non-zero temporal mismatch to the master cavity. Additional pulse shortening and stabilization is performed by the additive pulse mode-locking mechanism arising from self-phase modulation due to a Kerr-type non-resonant nonlinearity in the host crystal of the laser amplifier.     

Features of the crystalline state of graphite layers

Pyrolytic graphite films prepared by means of microsplitting are studied. In the samples, the alternation of pentagonal and hexagonal symmetry planes is revealed. These graphite crystal states can be classified as mesoscopic fullerene-like structures.     

Formation of square-order areas on the colloidosome surface

The self-assembly of the colloidosome, i.e., the system of rather densely packed colloidal particles arranged at the spherical interface of two phases, has been simulated. Particles are retained on the sphere surface by surface tension and are ordered due to the interaction described by the Lennard-Jones potential. The particle coordinates are obtained by conditional minimization of the free energy of the system. The violations of the average hexagonal order of colloidosome surface particles, not reduced to the topologically caused formation of pentagonal point defects, are studied. It is shown that the average area excess per colloidal particle can cause the formation of square-order areas observed in colloidosomes.     

含色散介质的一维光子晶体微腔的透射谱

研究了含色散介质的一维光子晶体微腔的透射谱,对色散介质采用Lorentz振子模型,腔模的频率设置在光子晶体带隙中心。发现当吸收可以忽略时,色散效应将导致在腔模附近有很高的态密度,与此相应地在透射谱中出现一个较宽的透射带。当吸收存在时透射带中心的透射峰消失,但带尾的透射峰依然存在。     

Stabilization of an optical cavity containing a birefringent element

A locking scheme for optimizing the length of an optical cavity containing a birefringent crystal is presented. This scheme is a variation on the well known polarization sensitive locking scheme. The birefringence of the crystal introduces a polarization dependent phase difference which can be used to generate a locking signal. The principles of the locking system are described and verified experimentally.     

偶极子位置及偏振对激发光子晶体H1微腔的影响

光子晶体微腔和量子点的集成是实现量子信息处理非常具有潜力的平台之一,利用微腔和量子点的耦合可以制备纠缠光子对,实现对量子态的操控.因为光子晶体微腔具有品质因子高、模场体积小等优点,可以极大地增强光与物质之间的相互作用,从而易于实现量子态在不同物理体系之间的转换.通过单量子点和光子晶体H1微腔的耦合可以产生纠缠光子对,因为H1微腔具有简并的、模式偏振正交的基态模式.通常微腔模式的激发随着量子点在微腔中的位置变化而改变,本文用时域有限差分方法研究了偶极子光源的位置及偏振对激发光子晶体H1微腔模式的影响.结果表明:通过改变偶极子光源位置可以选择性地激发H1微腔简并模式中的一个;具有某一偏振的偶极子光源只能激发相应偏振的微腔模式;模式激发强度的大小也是由偶极子光源在微腔中的位置决定的.鉴于目前量子点在微腔中的位置尚不能精确控制,所以微腔模式受激发光源位置的影响的研究具有重要意义.     

Sonochemical synthesis and characterization of new seven coordinated zinc,cadmium and mercury nitrate complexes: New precursors for nanostructure metal oxides

The nitrate complexes of group 12 elements with a tridentate Schiff base ligand (L = (E)-N1-((E)-3- phenylallylidene)-N2-(2-((E)-((E)-3-phenylallylidene) amino)ethyl) ethane-1,2-diamine) were synthesized via sonochemical process and characterized by various physical and chemical methods. The structural analysis of the zinc nitrate complex by single crystal X-ray diffraction analysis shows that the central atom is seven-coordinated by three nitrogen atoms from the Schiff base ligand as well as four oxygen atoms from two different nitrate anions. The geometry around the metal center can be described as a distorted pentagonal bipyramid. The crystal packing analysis of zinc nitrate complex indicates that the intermolecular interactions related to nitrate groups plays the essential role in the orientation of supramolecular structure. Hirshfeld surfaces (HS) and their corresponding fingerprint plots (FP) have been also used for further investigation of crystal structure of zinc nitrate complex. Furthermore thermal analyses (TG/DTG) of three nanostructure complexes were carried out and discussed. Finally, direct thermolysis of zinc and cadmium nitrate complexes in air atmosphere led to the production of zinc and cadmium oxide nanoparticles.     

Numerical modeling of photorefractive crystals for self-adapting external cavity laser mirrors

The process of refractive index grating formation in a photorefractive crystal, used as the self-adapting spectral filter in an external cavity of a semiconductor laser, is studied using a self-consistent model. The model is based on the Finite Difference solution of the Kukhtarev equations. The results obtained are compared with the ones provided by approximate analytical models.     

Formation of a pentagonal particle structure from copper nanoclusters

The structure of pentagonal particles and the processes of their formation from nanoclusters with the fifthorder symmetry axes are investigated by the methods of computer modeling and scanning electron-ion microscopy using copper as an example. It is demonstrated that the mechanism of cluster growth to pentagonal particles can be realized at which the volumetric stress present in noncrystal clusters will be released without breaking of the fifth-order symmetry of the growing cluster shape. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 27–32, February, 2009.     

Phase transitions in small particles formed at the initial stages of electrocrystallization of metals

The diagram of possible phase transitions occurring in small particles with variations in the electrodeposition parameters is constructed and justified using the data obtained from experimental investigations into the formation and evolution of pentagonal crystals on an indifferent substrate during electrocrystallization of copper.     

Atomic structure of Sr0.75Ba0.25Nb2O6 single crystal and composition-structure-property relationin (Sr,Ba)Nb2O6 solid solutions

The structure of the Sr_0.75Ba_0.25Nb₂O₆ single crystal has been investigated by x-ray diffraction. The occupancies of the Ba and Sr sites in two structural channels are determined. It is found that these sites are split in the large (pentagonal) channel. A qualitative correlation is revealed between the smearing of the phase transition and the displacement of the Sr atom from the m symmetry plane in the pentagonal channel at different [Sr]/[Ba] ratios. The degree of acentricity of the NbO₆ octahedra is analyzed as a function of the [Sr]/[Ba] ratio.     

激光间接驱动聚变柱形靶腔内光束传输研究

应用衍射积分理论, 对激光在间接驱动聚变柱形靶腔内的传输特性进行了研究, 给出了柱形腔靶注入孔以及内壁上的光强分布, 并与几何光学方法所得结果进行比较, 得出几何光学方法的适用条件。     

Poisson Lie groups and pentagonal transformations

Symplectic pentagonal transformations are intimately related to global versions of Poisson Lie groups (Manin groups, S ^*-groups, or symplectic pseudogroups). Symplectic pentagonal transformations of cotangent bundles, preserving the natural polarization, are shown to be in one to one correspondence with pentagonal transformations of the base manifold with a cocycle (if the base is connected and simply connected). By the results of Baaj and Skandalis, this allows to quantize (at the C ^*-algebra level!) those Poisson Lie groups, whose associated symplectic pentagonal transformation admits an invariant polarization. The (2n)²-parameter family of Poisson deformations of the (2n+1)-dimensional Heisenberg group described by Szymczak and Zakrzewski is shown to fall into this case.Supported by Alexander von Humboldt Foundation. On leave from Department of Mathematical methods in Physics, Warsaw University, Poland.     

过剩压晶种法生长金刚石过程中的浮力效应及其影响

 在合成金刚石的“过剩压晶种法”中,通过适当设计合成腔组装、晶种植种方式及位置、合成条件的选择,观察到在高温高压条件下,晶种在熔化金属触媒中上浮并生长的现象。这一现象是金属与金刚石比重不同而引起的。实验发现,晶种上浮现象与合成条件有密切的关系,适当高的温度与压力是必要的。浮力效应对过剩压晶种法中,金刚石的连聚晶形成及晶体形态,都有一定的影响。     

Defect formation in a carbon onion upon irradiation with Ar ions

The interaction of an Ar ion with a C₆₀@C₂₄₀@C₅₄₀ carbon onion and an Ar ion beam with a C₆₀@C₂₄₀@C₅₄₀@C₉₆₀ carbon onion are studied by molecular dynamics. The energy threshold for the formation of a vacancy in a pentagon of the onion fullerene shell is examined in two temperature regimes (300 and 1000 K). The main types of defects formed in the onion structure at various incident ion energies are detected and described. It is shown that the pentagonal cycles with their nearest environment are the least stable regions in the carbon onion under irradiation. The results obtained provide direct confirmation of the possibility of formation of a diamond structure upon ion irradiation of carbon onions.     

Conjugation of phases in pyroboroncarbon

Electron microscopy studies of nanoparticles in pyroboroncarbon reveal the pentagonal symmetry of their structure. The nanoparticles consisting of crystal individuals separated by twinning boundaries have icosahedral faceting (habit). As a result of the analysis of experimental high-resolution microphotographs of the nanoparticles via the digital processing of images based on fast Fourier transform, the conditions of phase conjugation in pyroboroncarbon are determined.     

Cavity Mode, Q Value and the Photon′s Lifetime in a Cavity Formed by Defected 2-Dimensional Photonic Crystal

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Cavity Mode, Q Value and the Photon′s Lifetime in a Cavity Formed by Defected 2-Dimensional Photonic Crystal

A complex frequency method to calculate the lifetime, Q value and field distribution of cavity mode in a defected 2D photonic crystal cavity is presented. Using this method, we analyze the cavity mode formed by a 2D photonic crystal with an interval “atom”. This method is also applicable to the defected 2D photonic crystal cavity of other structures. Cavity formed by a 2D random photonic crystal is discussed.