Compact setup for reflection holography with Bi12TiO 20 crystals

A novel optical setup for imaging through reflection holography with Bi12TiO20 (BTO) sillenite photorefractive crystals is proposed. Aiming a compact, robust and simple optical setup the lensless Denisiuk arrangement was chosen, using a He-Ne red laser as light source. In this setup the holographic medium is placed between the light source and the object. The beam impinging the crystal front face is the reference one, while the light scattered by the surface is the object beam in a holographic recording by diffusion. In order to allow the readout of the diffracted wave only and to keep the setup simplicity a polarizing beam splitter cube (PBS) was positioned at the BTO input. The reference beam is s-polarized (polarization direction perpendicular to the table top) and the crystal. 〈001〉-axis is rotated by an angle γ with respect to the input polarization in order to make the transmitted object beam and the diffracted beam to have orthogonal polarizations. While the transmitted wave is reflected by the PBS at a right angle, the diffracted wave carrying the holographic reconstruction of the object passes through the PBS, being collected by a positive lens in order to form the holographic image at a CCD camera. The holographic recording with the grating vector is parallel to the 〈100〉-axis. An expression for the diffracted wave intensity as a function of γ was derived, and this relation was experimentally investigated. © 2008 American Institute of Physics.

Calibration of cosmogenic noble gas production in ordinary chondrites based on 36 Cl- 36 Ar ages. Part 1: Refined produced rates for cosmogenic 21 Ne and 38 Ar

We measured the concentrations and isotopic compositions of He, Ne, and Ar in bulk samples and metal separates of 14 ordinary chondrite falls with long exposure ages and high metamorphic grades. In addition, we measured concentrations of the cosmogenic radionuclides 10Be, 26Al, and 36Cl in metal separates and in the nonmagnetic fractions of the selected meteorites. Using cosmogenic 36Cl and 36Ar measured in the metal separates, we determined 36Cl-36Ar cosmic-ray exposure (CRE) ages, which are shielding-independent and therefore particularly reliable. Using the cosmogenic noble gases and radionuclides, we are able to decipher the CRE history for the studied objects. Based on the correlation 3He/21Ne versus 22Ne/21Ne, we demonstrate that, among the meteorites studied, only one suffered significant diffusive losses (about 35%). The data confirm that the linear correlation 3He/21Ne versus 22Ne/21Ne breaks down at high shielding. Using 36Cl-36Ar exposure ages and measured noble gas concentrations, we determine 21Ne and 38Ar production rates as a function of 22Ne/21Ne. The new data agree with recent model calculations for the relationship between 21Ne and 38Ar production rates and the 22Ne/21Ne ratio, which does not always provide unique shielding information. Based on the model calculations, we determine a new correlation line for 21Ne and 38Ar production rates as a function of the shielding indicator 22Ne/21Ne for H, L, and LL chondrites with preatmospheric radii less than about 65 cm. We also calculated the 10Be/21Ne and 26Al/21Ne production rate ratios for the investigated samples, which show good agreement with recent model calculations.

Multiband photoluminescence from carbon nanoflakes synthesized by hot filament CVD: towards solid-state white light sources

Carbon nanoflakes (CNFLs) are synthesized on silicon substrates deposited with carbon islands in a methane environment using hot filament chemical vapor deposition. The structure and composition of the CNFLs are studied using field emission scanning electron microscopy, high-resolution transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy. The results indicate that the CNFLs are composed of multilayer graphitic sheets and the area and thickness of CNFs increase with the growth time. The photoluminescence (PL) of CNFLs excited by a 325 nm He-Cd laser exhibits three strong bands centered at 408, 526, and 699 nm, which are related to the chemical radicals terminated on the CNFLs and the associated interband transitions. The PL results indicate that the CNFLs are promising as an advanced nano-carbon material capable of generating white light emission. These outcomes are significant to control the electronic structure of CNFLs and contribute to the development of next-generation solid-state white light emission devices. © 2014 the Partner Organisations.

Theoretical gain optimization studies in 10.6 µm CO2-N2 gasdynamic lasers. IV. Further results of parametric study

Based on a method proposed by Reddy and Shanmugasundaram, similar solutions have been obtained for the steady inviscid quasi-one-dimensional nonreacting flow in the supersonic nozzle of CO2-N2-H2O and CO2-N2-He gasdynamic laser systems. Instead of using the correlations of a nonsimilar function NS for pure N2 gas, as is done in previous publications, the NS correlations are computed here for the actual gas mixtures used in the gasdynamic lasers. Optimum small-signal optical gain and the corresponding optimum values of the operating parameters like reservoir pressure and temperature and nozzle area ratio are computed using these correlations. The present results are compared with the previous results and the main differences are discussed. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Irradiation effects in graphene and related materials

Nanomaterials with a hexagonally ordered atomic structure, e.g., graphene, carbon and boron nitride nanotubes, and white graphene (a monolayer of hexagonal boron nitride) possess many impressive properties. For example, the mechanical stiffness and strength of these materials are unprecedented. Also, the extraordinary electronic properties of graphene and carbon nanotubes suggest that these materials may serve as building blocks of next generation electronics. However, the properties of pristine materials are not always what is needed in applications, but careful manipulation of their atomic structure, e.g., via particle irradiation can be used to tailor the properties. On the other hand, inadvertently introduced defects can deteriorate the useful properties of these materials in radiation hostile environments, such as outer space. In this thesis, defect production via energetic particle bombardment in the aforementioned materials is investigated. The effects of ion irradiation on multi-walled carbon and boron nitride nanotubes are studied experimentally by first conducting controlled irradiation treatments of the samples using an ion accelerator and subsequently characterizing the induced changes by transmission electron microscopy and Raman spectroscopy. The usefulness of the characterization methods is critically evaluated and a damage grading scale is proposed, based on transmission electron microscopy images. Theoretical predictions are made on defect production in graphene and white graphene under particle bombardment. A stochastic model based on first-principles molecular dynamics simulations is used together with electron irradiation experiments for understanding the formation of peculiar triangular defect structures in white graphene. An extensive set of classical molecular dynamics simulations is conducted, in order to study defect production under ion irradiation in graphene and white graphene. In the experimental studies the response of carbon and boron nitride multi-walled nanotubes to irradiation with a wide range of ion types, energies and fluences is explored. The stabilities of these structures under ion irradiation are investigated, as well as the issue of how the mechanism of energy transfer affects the irradiation-induced damage. An irradiation fluence of 5.5x10^15 ions/cm^2 with 40 keV Ar+ ions is established to be sufficient to amorphize a multi-walled nanotube. In the case of 350 keV He+ ion irradiation, where most of the energy transfer happens through inelastic collisions between the ion and the target electrons, an irradiation fluence of 1.4x10^17 ions/cm^2 heavily damages carbon nanotubes, whereas a larger irradiation fluence of 1.2x10^18 ions/cm^2 leaves a boron nitride nanotube in much better condition, indicating that carbon nanotubes might be more susceptible to damage via electronic excitations than their boron nitride counterparts. An elevated temperature was discovered to considerably reduce the accumulated damage created by energetic ions in both carbon and boron nitride nanotubes, attributed to enhanced defect mobility and efficient recombination at high temperatures. Additionally, cobalt nanorods encapsulated inside multi-walled carbon nanotubes were observed to transform into spherical nanoparticles after ion irradiation at an elevated temperature, which can be explained by the inverse Ostwald ripening effect. The simulation studies on ion irradiation of the hexagonal monolayers yielded quantitative estimates on types and abundances of defects produced within a large range of irradiation parameters. He, Ne, Ar, Kr, Xe, and Ga ions were considered in the simulations with kinetic energies ranging from 35 eV to 10 MeV, and the role of the angle of incidence of the ions was studied in detail. A stochastic model was developed for utilizing the large amount of data produced by the molecular dynamics simulations. It was discovered that a high degree of selectivity over the types and abundances of defects can be achieved by carefully selecting the irradiation parameters, which can be of great use when precise pattering of graphene or white graphene using focused ion beams is planned.

Dynamics of the chemical bond: inter- and intra-molecular hydrogen bond

In this discussion, we show that a static definition of a `bond' is not viable by looking at a few examples for both inter-and intra-molecular hydrogen bonding. This follows from our earlier work (Goswami and Arunan, Phys. Chem. Chem. Phys. 2009, 11, 8974) which showed a practical way to differentiate `hydrogen bonding' from `van der Waals interaction'. We report results from ab initio and atoms in molecules theoretical calculations for a series of Rg center dot center dot center dot HX complexes (Rg = He/Ne/Ar and X = F/Cl/Br) and ethane-1,2-diol. Results for the Rg center dot center dot center dot HX/DX complexes show that Rg center dot center dot center dot DX could have a `deuterium bond' even when Rg center dot center dot center dot HX is not `hydrogen bonded', according to the practical criterion given by Goswami and Arunan. Results for ethane-1,2-diol show that an `intra-molecular hydrogen bond' can appear during a normal mode vibration which is dominated by the O center dot center dot center dot O stretching, though a `bond' is not found in the equilibrium structure. This dynamical `bond' formation may nevertheless be important in ensuring the continuity of electron density across a molecule. In the former case, a vibration `breaks' an existing bond and in the later case, a vibration leads to `bond' formation. In both cases, the molecule/complex stays bound irrespective of what happens to this `hydrogen bond'. Both these cases push the borders on the recent IUPAC recommendation on hydrogen bonding (Arunan et al. Pure. Appl. Chem. 2011, 83 1637) and justify the inclusive nature of the definition.

用激光双镜干涉仪测量自然对流的温度场

<正> 在某些科研领域中,测量密度(温度)空间的分布是十分重要的。阴影仪、纹影仪等便于定性观察,要定量是十分困难的。M-Z干涉是一种较好的定量测量手段,但是由于它的光学元件要求苛刻,造价昂贵,使用调整比较复杂,所以在使用上就有一定的局限性。有了激光以后,对M-Z干涉仪的某些要求就大大地缓和了。 激光双镜干涉仪具有M-Z干涉仪定量方便的特点,又具有结构简单,操作调整方便等优点。它是以扩束准直的He-Ne激光为光源,由两块平面平晶做干涉元件的不等程干涉仪,被测对象置于两块平晶之间。其原理示意图见图1。

用于流场显示的激光双镜干涉仪

研制的激光双镜干涉仪比马赫-陈得尔干涉仪除具有较高的干涉光束强度、更大的视场口径、更好的抗振性、结构更简单及成本很低等优点外,还具有与马赫干涉仪完全相同的干涉信息处理方法,并且灵敏度还高一倍。干涉条纹的方向与宽度可任意调节。不需苛刻的实验环境和复杂的调节过程,适于大多数流场干涉显示的定量研究。 文中将讨论仪器的原理及特点,并给出部份实际应用中的结果。

硅对强CO_2激光的雪崩吸收及其后果

<正> 作者测量Si片在强CO_2激光辐照下透射率T和温度θ的变化时看到,Si的透射率到某一时刻突然降为θ,而恰在此时的Si的温升速率呈现极大。从载流子费米统计和光吸收截面计算出的T-θ曲线与实验一致,这说明强CO_2激光辐照引起的载流子热激发反过来导致Si雪崩式地增强吸收CO_2激光,使硅表现出非线性的性质。基于这一能量耦合机理作了如下研究。 M.Miyao等人证实一定功率密度的CO_2激光辐照可使注磷Si 100％电激活,本文发现在这个过程中注磷si对CO_2激光和对He-Ne激光的反射率朝相反的方向跃变。红外分光光

强CO_2激光照射靶面的现象

在强激光对靶材的作用中,以连续及脉冲CO_2激光为主光源,首先研究了发生于靶前区的现象,用高速干涉摄影术来诊断,判别出连续激光引起烧坑形成的时间及蒸汽羽喷向的扭转过程,并观察了脉冲激光引起等离子体的发展、空气击穿及产生冲击波运动和蒸汽羽等非自发光现象,使用了脉冲He-Ne激光高速干涉摄影装置。

强CO_2激光辐照下离子注入Si反射率的动态干涉效应

本文从理论和实验研究了连续CO_2激光辐照下磷离子注入Si对He-Ne激光束反射率呈现的动态干涉效应。从反射强度随时间的变化看出,Si片离子注入层固相外延的速率在整个再结晶过程中是不均匀的。

研究快速现象的高速干涉摄影系统

我们研制了一种用于诊断TEACO_2脉冲激光与物质相互作用,以及其它流场中快速现象的高速干涉摄影系统;解决了这一技术中的时间同步、高速摄影机与激光平晶错位干涉仪的光学匹配;提出了逆程序运转方案,将连续输出的He-Ne激光改成了时间可控的脉冲光源;用这一技术拍出了一系列相互作用过程的微秒级高速干涉照片,以及超音速风洞中流场照片。这种技术也能广泛用于其它快速现象及流场显示领域中。

一种基于衍射光栅光束质量M^2因子的实时检测技术

提出了一种新的光束质量膨因子实时检测技术，利用一个普通正交衍射光栅组将一束待测激光束分成3×3共9路光，并利用光路调整器使9路光束通过不同的光程后有序地排列在CCD相机的探测面上，并使得各路光的光程差分布在束腰附近两倍瑞利距离内，从而可利用单一CCD探测面来同时获取待测光束多个位置上的光斑图样。再利用二阶矩理论求出各个位置上的光束束宽，通过曲线拟合进而实现光束质量的实时检测。结果表明，对于连续He-Ne激光器的输出光束，采用实时检测技术得到的测量结果与用传统方法得到的结果基本一致。

Effect of the variation of temperature on the structural and optical properties of ZnO thin films prepared on Si (111) substrates using PLD

ZnO thin films were prepared on Si (1 11) substrates at various temperatures from 250 to 700 degrees C using pulsed laser deposition (PLD) technique in order to investigate the structural and optical properties of the films. The structural and morphological properties of the films were investigated by XRD and SEM measurements, respectively. The quality of the films was improved with the increase of the temperature. By XRD patterns the FWHMs of the (0 0 2) peaks of the ZnO films became narrower when the temperatures were above 500 degrees C. The FWHMs of the peaks of (0 0 2) of the films were as narrow as about 0. 19 degrees when films were grown at 650 and 700 degrees C. This indicates the superior crystallinity of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The two strongest UV peaks were found at 377.9 nm from ZnO films grown at 650 and 700 degrees C. This result is consistent with that of the XRD investigation. Broad bands in visible region from 450 to 550 nm were also observed. Our works suggest that UV emissions have close relations with not only the crystallinity but also the stoichiometry of the ZnO films. (c) 2005 Elsevier Ltd. All rights reserved.

激光热透镜光度分析方法研究

实验部分的报告Ⅰ、Ⅱ为TLS方法原理性的实验。报告Ⅰ中，采用He-Ne激光器单光束热透镜实验装置，以Zr(IV)为工作对象，讨论了盐酸酸度、水溶性有机溶剂丙酮、乙醇等对Zr(IV)-偶氮胂Ⅲ络合物的吸光度、稳定性、TLS信号强度等影响，及L-C距、激光工作电流、探测头光孔径、切光调制频率等各实验参量对TLS信号的影响。在最佳工作条件下，对Zr(IV)的分析检出限达到21ng/mt，线性工作范围0.02 ～ 0.8 μg/mt。对铜基合金中锆的含量做了测定，结果符合样品标定的含量范围，测量的相对标准偏差为8.4%。遗憾的是所选择的样品中的Zr含量较高。报告Ⅱ在Ⅰ的基础上，用同一实验装置对Co(III)-PAN/氯仿体系进行了单吸收池、双吸收池的TLS方法的对比，利用激光热透镜效应在激光束腰前后两个共焦距位置上会聚性和发散性的反对称性十分方便地实现了扣除背景的目的。单池和双池对Co(III)的最低可测浓度分别达到5ng/mt和2ng/mt。在氯仿介质中使用zmw He-Ne激光器，增强因子E值达到10。