Dispersion measurements of water with white-light interferometry

We measure the second- and third-order dispersion coefficients, d(2)k/domega(2) and d(3)k/domega(3), of water for wavelengths from 0.45 to 1.3 mum using a Michelson white-light interferometer. In this interval, the second-order dispersion ranges from 0.068 to -0.1 fs(2)/mum, and the third-order dispersion ranges from 0.048 to 1.18 fs(3)/mum. We observe an oscillation in d(2)k/domega(2) near 1.1 mum that is due to water absorption features near that wavelength. From the dispersion coefficients, derivatives of the index of refraction of water are calculated and compared with available equations. These measured values of d(2)n/dlambda(2) and d(3)n/dlambda(3) should be useful in the evaluation and improvement of existing equations for n(lambda) in water.     

Measurement of group delay dispersion of high numerical aperture objective lenses using two-photon excited fluorescence

We determined the group-delay dispersion (GDD) of five microscope objectives by measuring the second-order autocorrelation at the focal points of the objectives with two-photon excited fluorescence as the power square sensor. We found that typical microscope lens systems introduce significant GDD (2000-6500 fs(2)). The third-order dispersion determined for these objectives limits the minimum obtainable pulse width at the focal point of an objective to 20-30 fs if not compensated. No significant chromatic aberration or higher-order dispersion effects were found for any of the optical components measured within the wavelength range of 700-780 nm and for pulse widths greater than 50-60 fs.     

Third-order dispersion in a pair of prisms

The general equation for third-order group velocity dispersion is derived in this paper, which contains all the terms of equation (11) in Arissian and Diels [1], as well as one extra term, which we have verified is not negligible. To verify our equation we have modeled the sum of Gaussian modulated frequencies. We show the electric field of bandwidth limited incident ultrashort pulses with a time duration of: 5 fs, 10 fs, 15 fs, 20 fs, 30 fs and 50 fs after propagating through a pair of identical isosceles prisms for a central frequency of 0.8 µm and 0.620 µm. The model is applied by using (a) the finite phase, (b) the phase approximated up to the second-order dispersion and (c) up to the third-order dispersion for each frequency component of the pulse. Graphs are presented for prisms made with fused silica and SF14.     

Na_2O-CaO-Al_2O_3-SiO_2-H_2O系水化物凝胶对Cs~+的吸附机理

在35℃恒温水化反应90d条件下,制备了Na2O-CaO-Al2O3-SiO2-H2O系水化物凝胶,探讨了水化物凝胶的化学组成对Cs+吸附性能的影响;讨论了水化物凝胶对Cs+的吸附热力学行为。结果表明,当化学组成为n(CaO+Na2O)/n(SiO2+Al2O3)=0.66,n(Al2O3)/n(SiO2)=0.3时,凝胶对Cs+的3d吸附量可达10.6936mg/g;温度越低,吸附量越大,凝胶对Cs+的吸附近似服从Freudlich、Langmuir和D-R吸附等温式,反应为放热反应,且以离子交换吸附为主;吉布斯自由能和吸附熵为均为负值,反应能自发进行。吸附动力学符合Lagergren假二级速率方程模型。     

SiO2/Mg（OH）2复合阻燃剂的阻燃性能研究

以SiO2/Mg(OH)2复合粉体为阻燃剂,与聚烯烃弹性体(POE)熔融共混制备了复合材料,采用灼热丝试验对其阻燃性能进行了测试,利用SEM和EDS观察POE复合材料的断面形貌、界面相容性及阻燃剂在基体中的分散行为,并对POE复合材料的力学性能进行了测试。结果表明SiO2/Mg(OH)2复合阻燃剂在POE中分散良好,界面相容性优良,具有良好阻燃效果,且可改善聚合物材料力学性能,是一种适宜推广的新型无机阻燃剂。     

Effects of excessive magnesium oxide and sintering regime on microstructure and dielectric properties of forsterite ceramics for millimeterwave dielectrics

Journal of Materials Science: Materials in Electronics - forsterite (Mg2SiO4) ceramic is an important millimeterwave dielectric ceramic with the advantages of low dielectric constant, high quality...     

Third-order dispersion effects generated by non-ideal achromatic doublets on sub-20 femtosecond pulses

Gaussian temporal envelope pulses with initial durations of 10?fs, 15?fs and 20?fs and a carrier wavelength of 810?nm were analyzed at the paraxial focal plane of non-ideal achromatic doublet lenses for well-collimated incoming pulses parallel to the optical axis. The wave vector is expanded up to third order, to investigate the effect of third-order group velocity dispersion on the pulse and the results are compared to those obtained when the wave number is expanded up to second order. The propagation time difference and the primary spherical aberration were included in the calculations using the thin lens approximation theory. Results are presented for a homogenous illumination beam.     

Three-systems theory of human visual motion perception: review and update

Lu and Sperling [Vision Res. 35, 2697 (1995)] proposed that human visual motion perception is served by three separate motion systems: a first-order system that responds to moving luminance patterns, a second-order system that responds to moving modulations of feature types-stimuli in which the expected luminance is the same everywhere but an area of higher contrast or of flicker moves, and a third-order system that computes the motion of marked locations in a "salience map," that is, a neural representation of visual space in which the locations of important visual features ("figure") are marked and "ground" is unmarked. Subsequently, there have been some strongly confirmatory reports: different gain-control mechanisms for first- and second-order motion, selective impairment of first- versus second- and/or third-order motion by different brain injuries, and the classification of new third-order motions, e.g., isoluminant chromatic motion. Various procedures have successfully discriminated between second- and third-order motion (when first-order motion is excluded): dual tasks, second-order reversed phi, motion competition, and selective adaptation. Meanwhile, eight apparent contradictions to the three-systems theory have been proposed. A review and reanalysis here of the new evidence, pro and con, resolves the challenges and yields a more clearly defined and significantly strengthened theory.     

Study of dispersion compensation in femtosecond lasers

Abstract

We present a formal analysis of dispersion compensation in femtosecond lasers and provide a detailed examination of the relevant features in Ti: sapphire and Cr: LiSAF lasers. It is shown that the essential of dispersion compensation up to the fourth order consists of searching for the solutions of a group of three linear equations. With the use of a prism pair, complete compensation of both the second- and the third-order dispersion corresponds to solving two of the three equations with the prism separation and the intraprism beam path length as variables. Owing to the limitations on the practically achievable prism separation and the intraprism path length in a laser set-up, only some of these solutions are physically meaningful; hence both zero second- and third-order cavity dispersion may be realized merely within a certain specific spectral range. The fourth-order dispersion, however, cannot be completely compensated for in this case unless a third control variable is introduced. It is also shown that the dominant parameter in determining the spectral region where dispersion is minimized is the difference between the ratio of the third-order dispersion to the second-order dispersion of the laser rod and that of the selected prism pair material. This also explains the major differences between Ti: sapphire and Cr: LiSAF lasers in terms of dispersion compensation.     

新型2-芳基咪唑并菲咯啉Ni(Ⅱ)配合物的合成及光学非线性

设计合成了3个新的含2-芳基-1H-咪唑并[4,5-f][1,10]菲咯啉的Ni(Ⅱ)配合物,用UV、IR、MS和元素分析进行了表征。采用飞秒激光,运用简并四波混频法,研究了Ni(Ⅱ)配合物在非共振状态下的三阶非线性光学性能。它们的三阶非线性光学极化率χ(3)为(3.99～4.36)×10-13esu,非线性折射率n2为(7.33～8.03)×10-12esu,分子二阶超极化率γ为(3.98～4.37)×10-31esu,响应时间τ为50～86fs。探索了配合物的分子结构对三阶非线性光学性能的影响。结果表明扩展π电子共轭体系,增强非平面分子内电荷转移等因素有利于获得较大的三阶光学非线性。     

Origin and effect of high-order dispersion in ultrashort pulse multiphoton microscopy in the 10 fs regime

Short pulses can induce high nonlinear excitation, and thus they should be favorable for use in multiphoton microscopy. However, the large spectral dispersion can easily destroy the advantages of the ultrashort pulse if there is no compensation. The group delay dispersion (GDD), third-order dispersion, and their effects on the intensity and bandwidth of second-harmonic generation (SHG) signal were analyzed. We found that the prism pair used for compensating the GDD of the two-photon microscope actually introduces significant negative high-order dispersion (HOD), which dramatically narrowed down the two-photon absorption probability for ultrashort pulses. We also investigated the SHG signal after GDD and HOD compensation for different pulse durations. Without HOD compensation, the SHG efficiency dropped significantly for a pulse duration below 20 fs. We experimentally compared the SHG and two-photon excited fluorescence (TPEF) signal intensity for 11 fs versus 50 fs pulses, a pulse duration close to that commonly used in conventional multiphoton microscopy. The result suggested that after adaptive phase compensation, the 11fs pulse can yield a 3.2- to 6.0-fold TPEF intensity and a 5.1-fold SHG intensity, compared to 50 fs pulses.     

Preparation and characterization of ceramic porous sheet composed of platelet (Cr, Al)2O3 crystals

A compact powder mixture consisting of 3Al2O3·2SiO2 (mullite) and Cr2O3, which was heated in a carbon powder bed, was cut into a 1 mm thickness sheet. The ceramic porous sheet composed of platelet (Cr, Al)2O3 crystals was prepared by leaching SiO2 contained in the sheet by hydrofluoric acid. The porous sheet produced from the 50 mass % mullite/50 mass % Cr2O3 compact, heated at 1500°C for 2 h, was composed of platelet crystals with 30 μm average length and 4.6 μm average thickness. Its relative density and specific surface area were 73 % and 4.4 m2 g-1 respectively. This revised version was published online in November 2006 with corrections to the Cover Date.     

Simple design method for third-order dispersion compensation with a thin-film dispersion compensator

A novel and simple numerical method for finding the best thin-film structures for third-order dispersion compensation has been achieved. A target third-order dispersion value is specified first; then the multilayer thin-film structure is optimized to have a second-order dispersion spectrum, which has the least deviation from linearity and has a slope that equals the specified third-order dispersion value. Numerical examples are presented for reflection-type and transmission-type thin-film compensators. Both types can achieve required phase compensation, but the reflection type has a flatter amplitude response than the transmission type.     

Intracavity frequency-doubled femtosecond cr(4+):forsterite laser

The generation of femtosecond optical pulses centered at ~620 nm directly from an all-solid-state laser oscillator is reported. Red pulses with pulse widths of the order of 170 fs were obtained with 24-mW average power at an 81-MHz repetition rate. They were achieved by intracavity frequency doubling of a mode-locked Cr(4+):forsterite laser with a 1-mm-thick beta-BaB(2)O(4) crystal. The process of laser mode locking was modified by surface coating the doubling crystal.     

Periodic and solitary wave solutions for ultrashort pulses in negative-index materials

Abstract

We present a detailed analysis for the existence of dark and bright solitary waves as also fractional-transform solutions in a nonlinear Schrödinger equation model for competing cubic–quintic and higher-order nonlinearities with dispersive permittivity and permeability. Parameter domains are delineated in which these ultrashort optical pulses exist in negative-index materials (NIMs). For example, dark solitons exist for the case of normal second-order dispersion, anomalous third-order dispersion, self-focusing Kerr nonlinearity, and non-Kerr nonlinearities, while the bright solitons exist for the case of anomalous second-order dispersion, normal third-order dispersion, self-focusing Kerr nonlinearity, and non-Kerr nonlinearities. This is contrary to the situation in ordinary materials.     

MgO-SiO2-ZrO2-C系复合材料显微结构及其抗蚀性研究

以锆英砂和电熔镁砂为原料,合成ZrO2增韧的镁橄榄石材料,进而加入鳞片状石墨,得到Mg2SiO4(-ZrO2)-C复合材料。用扫描电镜、X射线衍射仪、差热、红外光谱等手段研究了该材料的显微结构和矿物组成。表明该材料具有优异的高温强度、抗侵蚀性和热震稳定性,是一种新型耐火材料。,The forsterite-zirconia material have been produced from the zircon and magnesia, adding graphite, to produce a Mg2SiOZrO2-C. The microstructure and Mineral composition have been studied by means of microscope, SFM,X-ray, diffractometer and DTA. It is a nice refractories that the brick have densed structure, thermal stability, good thermal conductivity and wear-resistance, and good resistance to the corrosion by iron-oxide slay.     

Enhanced field emission properties of vertically aligned double-walled carbon nanotube arrays

Vertically aligned double-walled carbon nanotube (VA-DWCNT) arrays were synthesized by point-arc microwave plasma chemical vapor deposition on Cr/n-Si and SiO(2)/n-Si substrates. The outer tube diameters of VA-DWCNTs are in the range of 2.5-3.8?nm, and the average interlayer spacing is approximately 0.42?nm. The field emission properties of these VA-DWCNTs were studied. It was found that a VA-DWCNT array grown on a Cr/n-Si substrate had better field emission properties as compared with a VA-DWCNT array grown on a SiO(2)/n-Si substrate and randomly oriented DWCNTs, showing a turn-on field of about 0.85?V?μm(-1) at the emission current density of 0.1?μA?cm(-2) and a threshold field of 1.67?V?μm(-1) at the emission current density of 1.0?mA?cm(-2). The better field emission performance of the VA-DWCNT array was mainly attributed to the vertical alignment of DWCNTs on the Cr/n-Si substrate and the low contact resistance between CNTs and the Cr/n-Si substrate.     

Highly crystalline Zeolite-A from flyash of bituminous and lignite coal combustion

Flyash is being generated in voluminous amounts by large scale coal combustion process. It poses a serious threat to thermal power industries specifically, in India, wherein the percent of utilisation of flyash is very poor (3-5%). In view of this problem, newer methods of its disposal and utilisation are being explored. The synthesis of zeolite from flyash appears to be one of the most promising alternatives as it has emphasis on value addition to waste material.Flyashes originating from different sources of coal differ in their characteristics and have implications in this work on Zeolite-A production. These factors have been thoroughly investigated and the conditions favourable for formation of Zeolite-A have been delineated. The reactivity of flyash towards zeolite formation is directly dependent on the SiO(2)/Al(2)O(3) ratio, Fe(2)O(3) and CaO content. Amongst the flyashes investigated, so far the sub-bituminous coal based flyash with SiO(2)/Al(2)O(3) ratio of 3.47 appears to be a suitable substrate for Zeolite-A synthesis. These zeolites have been characterised with respect to XRD crystallinity, calcium binding capacity (CBC) and sorption capacity, wherein the crystallinity ranges from 50 to 100%, the CBC ranges from 290 to 560meq/100g and sorption capacity ranges from 16.6 to 23.8%.     

Shape evolution of a light pulse in a linear birefringent medium

The spreading of a three-dimensional quasi-monochromatic progressive directional wave packet (such as a laser pulse) propagating freely in a linear and transparent birefringent medium is described geometrically by means of the ellipsoid representative of the pulse's second-order moments. The medium is characterized by a second-order expansion of its dispersion relation omega(K) about the mean wave vector Km of the pulse, i.e., by its Hessian matrix (H(Km)omega), which plays two important roles. Then, for some elements of(H(Km)omega), practical expressions are provided that are related to the curvature and dispersion properties of the normal surface of the medium. Then cases in which these properties determine completely the asymptotic transverse or axial spreadings of the wave packet are specified, and the results of an experiment are discussed.     

Structure and electrical properties of (111)-oriented Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 thin film for ultra-high-frequency transducer applications

Ternary lead magnesium niobate-lead zirconate titanate system 0.4Pb(Mg(1/3)Nb(2/3))O(3)-0.25PbZrO(3)-0.35PbTiO(3) (40PMN-25PZ-35PT) thin film with a thickness of 1.5 μm was grown on Pt(111)/Ti/SiO(2)/Si substrate via chemical solution deposition. X-ray diffraction and transmission electron microscopy results suggested the film obtained was highly (111)-oriented. The remanent polarization and coercive electric field of the film were found to be 25.5 μC/cm(2) and 51 kV/cm, respectively. In addition, at 1 kHz, the dielectric constant was measured to be 1960 and the dielectric loss 0.036. The film was observed to undergo a diffuse ferroelectric-to-paraelectric phase transition at around 209°C. The leakage current appeared to depend on the voltage polarity. If the Au electrode was biased positively, the leakage current was dominated by the Schottky emission mechanism. When the Pt electrode was biased positively, the conduction current curve showed an ohmic behavior at a low electric field and space-charge-limited current characteristics at a high electric field.