Optical properties of vanadium oxides-an analysis

In this study, the optical properties of bulk and thin films of VO₂, V₂O₃, and V₂O₅, deposited on Al₂O₃ substrates, have been analyzed from infrared to vacuum ultraviolet range (up to 12 eV). Utilizing the available data of wavelength dependent optical constants of these materials in the literature, the energy corresponding to the peaks in the imaginary part of the dielectric function (ε ₂–R spectra), have been interpreted and compared as a function of structure, polarization, and temperature. The energies corresponding to the peaks in reflectivity-energy (R–E) spectra are explained in terms of the Penn gap (E _p). E _p values for VO₂ and V₂O₅ are close to the average of energies corresponding to the peaks ( $ \bar{E} $ E ¯ ) while, their values are even closer in V₂O₃, reflecting the degree of anisotropy in the order of V₂O₃ < VO₂ < V₂O₅. The first order reversible, insulator to metal phase transition (IMT) of both bulk and thin films of the V–O systems are studied as an effect of temperature change. The effective number of electrons, n _eff, participating in the optical transitions is described from the numerical integration using the well-known sum rule. The change in n _eff with respect to the energy of incident photons is also calculated and it is found that this change is consistent with the peaks observed in the ε ₂–E spectra.     

Optical transmission decay dynamics in dual-frequency nematic liquid crystal cells

We have experimentally studied the S-effect dynamics in a dual-frequency nematic liquid crystal (NLC) cell. It is demonstrated that the optical transmission rise and decay times depend on the mode of control over the NLC director orientation in an applied electric field, including the rectangular (square-wave) dc voltage pulses and sinusoidal low-and high-frequency addressing schemes. It is established that the presence of a thin dielectric layer of amorphous hydrogenated carbon (a-C:H) at the NLC boundary can decrease by an order of magnitude the transmission decay time under the action of a high-frequency voltage as compared to the case of natural elastic relaxation in a cell where only the rise time is controlled.     

Magnetooptical Kerr effect measurements of ultrafast spin dynamics in cobalt nanodots

We present our magnetooptical Kerr effect (MOKE) studies on picosecond spin dynamics in closely spaced rectangular Co dots with sizes ranging from 2/spl times/6 /spl mu/m/sup 2/ down to 100 /spl times/ 300 nm/sup 2/ under in-plane, picosecond, magnetic pulse excitation. A low-temperature-grown GaAs photoconductive switch, excited by femtosecond laser pulses, was used to produce /spl sim/25-ps-long magnetic transients along the surface of the coplanar-waveguide centerline, which contained arrays of patterned Co dots. The resulting spin dynamics in the dots was detected by a time-synchronized train of femtosecond optical probe pulses employing the time-resolved MOKE. Our experimental technique allowed us to measure the initial picosecond dynamics of spins in Co nanodots, followed by damped oscillations. We ascribe the observed results to the small-angle coherent spin precession and show that it depends on the size of magnetic dots.     

酞菁铜/氧化钛纳米复合薄膜的制备及其光导性能的研究

通过电化学阳极氧化法在Ti片上制备了氧化钛(TiO2)纳米管阵列.用这种高度有序的阵列结构作为模板,利用电泳沉积的方法在模板表面沉积了一种有机半导体材料酞菁铜(CuPc),从而得到了CuPc/TiO2有机/无机纳米复合结构.通过场发射扫描电镜(FESEM),透射电镜(TEM)等手段对这种复合结构的表面形貌及结构进行了表征.能谱数据证实了复合结构中有机物的存在.此外,CuPc薄膜的形貌和结构可以通过改变电泳沉积参数(如沉积时间和电压)进行调控,从而得到相应的纳米晶、纳米线和微米线薄膜.用该复合薄膜作为载流子发生层制备的双层光导体的光导性能测试结果表明,与复合前的氧化钛薄膜相比,该复合薄膜的光敏性有明显的提高.     

Signal-to-noise Ratio of Optical System Consisting of Squeezer and Optical Kerr Medium

Abstract

In this paper, we analyse the properties of a quantum state transformation system consisting of a squeezer and an optical Kerr medium. An average, a variance, and a signal-to-noise ratio (SNR) of a quadrature-phase amplitude are calculated analytically. We show that the SNR is increased by this system; in particular the use of a squeezer with a large squeezing gain gives a drastic improvement in the SNR. Furthermore, the reason for the improvement in SNR and the usefulness of the squeezed state are discussed.     

The effect of a linear mode coupling dispersionon the wave packet dynamics in an optical waveguide with Kerr nonlinearity

The influence of a dispersion of the linear mode coupling coefficient of an optical waveguide (OWG) with Kerr nonlinearity on the dispersion parameters and dynamics of an optical pulse propagating in such a system is studied. In OWGs with a strong linear mode coupling, the presence of a dispersion of the mode coupling may lead to a significant decrease in the energy threshold for nonlinear self-compression of pulses as compared to the case of a single-mode OWG.     

Optical absorption of vanadium in sodium diborate glasses

The optical absorption in blown films and bulk specimens of sodium diborate glasses containing vanadium oxide based on the system [Na₂O-2B₂O₃]_1?x [V₂O₅] _x , wherex = 0, 0.05, 0.10, 0.15 and 0.20, has been studied in the wavelength range 200 to 900 nm. The fundamental absorption edge has been analysed in the light of the existing models. It is found that glasses containing a higher content of vanadium have fewer defects when compared with those containing a low vanadium content. The absorption spectra are interpreted as due solely to pentavalent vanadium.     

Absence of a self-induced decay effect in Au

We report the results of an improved experiment aimed at determining whether the half-life (T_1/2) of ¹⁹⁸Au depends on the shape of the source. In this experiment, the half-lives of a gold sphere and a thin gold wire were measured after each had been irradiated in the NIST Center for Neutron Research. In comparison to an earlier version of this experiment, both the specific activities of the samples and their relative surface/volume ratios have been increased, leading to an improved test for the hypothesized self-induced decay (SID) effect. We find T_1/2(sphere)/T_1/2(wire)=(0.9993±0.0002), which is compatible with no SID effect.     

Optical free-path-length distribution in a fractal aggregate and its effect on enhanced backscattering

A free-path-length distribution function (FPDF) of multiply backscattered light is theoretically derived for a fractal aggregate of particles. An effective mean-free path-length l(D) is newly introduced as a measure of randomness analogous with a homogeneously random medium. We confirm the validity of the FPDF by demonstrating agreement between the dimensions designed for a particle distribution generated by a random walk based on the derived FPDF and estimated by the radius of gyration method. The FPDF is applied to Monte Carlo simulations for copolarized multiply backscattered light from the fractal aggregate of particles. It is shown that a copolarized intensity peak of enhanced backscattering in the far field decreases in accordance with theta(2-D) and has an angular width of lambda/l(D). This spatial feature of the backscattering enhancement corresponds to that of the copolarized intensity peak produced from a homogeneously random medium with a dimension of D = 3. As a result, the validity of the model for the fractal structure of particle aggregates and the applicability of the derived FPDF are confirmed by the numerical results.     

Quantum correlation in dephasing decay and its effect on interference in three-level systems

The quantum correlation in dephasing decay can be realized, when the energy fluctuations of transition frequencies are synchronized. The correlation in the three-level atom systems will enhance the interference in the absorption and change the nature of the interference, from destructive to constructive in cascade low-driving three-level atom and from constructive to destructive in V-type three-level atom. The quantum correlation is observed by properly introducing the collision or time-dependent magnetic field through the increase or decrease of the resonant absorption.     

Preparation of a novel class of phthalocyanine containing cross-linked polymers and their thin films

Prepolymers containing vanadyl phthalocyanines, prepared by the reaction of amino-substituted vanadyl phthalocyanines and diglycidyl ether of biphenol A, can be cured to give transparent network polymeric films, which show absorptions at 780 nm and 820 nm, respectively. The films are stable to organic solvents, inorganic bases and acids. Ultrafast optical responses were observed for both polymers with typical decay time of about 240 fs.     

MEMS用新型微型超级电容器的制造及性能分析

采用微加工工艺为MEMS制作了一种基于电化学赝电容原理储能的微型能量存储器件——新型微型超级电容器.通过光刻、感应耦合等离子体刻蚀和溅射等MEMS微加工工艺制作了硅基3D微电极阵列,并在其表面用阴极电沉积法制备了氧化钌功能薄膜.采用循环伏安法和交流阻抗法研究了3D微电极的性能,系统比较了3D微电极与平面微电极的电化学性能,测试结果表明3D微电极的比电容达1.57F· cm-2.基于三维微电极阵列阳极和钌钛金属氧化物阴极组装了微型超级电容器,恒流充放电测试结果表明该电容器的比容量达0.73F·cm-2,比功率达0.50mW·cm-2,比能量达0.36J·cm-2.     

Vortex dynamics and decay of supercurrent in 2-d superconductors

The decay of supercurrent in a 2-d superconductor through the homogenous quantum nucleation of vortex-antivortex pairs is formulated as a (2+1)-d scalar quantum electrodynamic problem. The calculation of the quantum decay rate can then be simplified to the usual single particle WKB calculation. We show explicitly that the homogeneous quantum nucleation of vortex-antivortex pairs is incompatible to the existence of the magnus force in the absence of dissipation, and point out more complicated nucleation processes needed to be studied by the vortex dynamics method in such case.     

Optical and photoelectric properties of manganese(II) phthalocyanine epoxy derivative

A novel soluble manganese(II) phthalocyanine (MnPc) epoxy derivative was synthesized and characterized by infrared (IR), electronic absorption spectrum and fluorescence spectrum. Fluorescence quantum yield of the derivative was measured in different solvents and reached 0.35 and 0.39 in dimethylsulfoxide (DMSO) and N, N-dimethylformamide (DMF), respectively. The derivative exhibits high solubility and excellent film-forming property. MnPc epoxy derivative can form cross-linked polymer films without the addition of high polymer. The current–voltage characteristics of films were measured in dark and under infrared irradiation.     

Kerr effect imaging of dynamic processes in magnetic recordingheads

Techniques for imaging microscopic dynamic magnetic phenomena in magnetic recording heads are reviewed. Two experimental apparatus which utilize the Kerr magnetooptic effect are described. A scanning magnetooptic photometer uses the principles of confocal optical microscopy in which a focused laser spot serves as a high-resolution (~0.3 μm) probe of magnetic activity to very high frequencies (250 MHz). Magnetooptic flash photography uses the technique of stroboscopic imaging with digital image processing to provide instantaneous (10 ns exposure time) images of magnetic phenomena on a microscopic scale by utilizing a pulse laser for illumination. Results from various studies of ferrite, metal-in-gap, and thin-film magnetic recording heads using these apparatus are reviewed along with their methods     

Precise energy of the weak 32-keV gamma transition observed in Kr decay

The energy of the weak isomeric 32 keV γ-transition in the ^83mKr decay was established to be 32151.7(5) eV. It has an intensity of only 0.055% per decay. This energy value was obtained from gamma spectrometry measurements of differences in the energies of closely spaced lines. This result allows one to determine more precisely the energy of the K conversion electron of this 32 keV transition, thus representing a unique tool for the energy calibration of the tritium beta spectrum that is measured in the KATRIN neutrino mass determination experiment.     

Optical Kerr switching technique for the production of a picosecond,multiwavelength CO2 laser pulse

A wavelength-independent method for optical gating, based on the optical Kerr effect, has been demonstrated. Using this method, we produced 100-ps, 10-kW, two-wavelength pulses (10.3 and 10.6 microm) with a signal-to-background ratio contrast of 10(5) by slicing a long CO2 pulse. The capability of gating consecutive pulses separated on a picosecond time scale with this method is also shown.     

一种新的扬声器功率测试系统设计及其不确定度分析

目的:为保证扬声器质量,研制了一种新的扬声器功率测试系统,并评估测试系统测量的准确性。方法:该系统以单片机作为中央处理器,采用直接数字频率合成技术提供输入信号,采用基于AD8436真有效值转换芯片的信号检测电路,测量信号经过A/D处理后发送至单片机,通过以太网通讯发给上位机进行扬声器功率的实时监测与分析,并对系统不确定度进行评定。结果:该测试系统的输出信号准确度优于0.01%,失真度小于0.5%,可以同时实现20路扬声器测试。结论:该系统在进行扬声器功率测试时,系统简单,准确度高,成本低,检测效率高,具有较高的实际应用价值。