The peculiarities of discrete diffraction in two-dimensional optical waveguide arrays

The fundamental peculiarities of discrete diffraction in the two-dimensional waveguide arrays were studied. The discrete diffraction properties of such arrays can be effectively altered, depending upon the input conditions. By slightly changing the input conditions, light can experience normal diffraction in one-direction and experience anomalous diffraction in the other.     

Evaluation of the cross-polarization modulation impact on the conversion efficiency of a four wave mixing process developed in a bulk-SOA

This paper addresses, theoretically and experimentally, the impact of the cross-polarization modulation (XPolM) phenomenon on the conversion efficiency of a four wave mixing (FWM) process taking place in a bulk-SOA with input signals linearly co-polarized at 0°, 45°, 90°, and −45°. Based on the experimental determination of the output polarization states of the pump and probe signals, a technique is proposed to incorporate the XPolM effect in classic models describing the FWM. It is demonstrated that classic models lacking the inclusion of the XPolM effect can reflect a significant error in the estimation of the conversion efficiency.     

ZnSe films deposited on crystalline GaAs and amorphous quartz substrates by means of pulsed laser ablation technique

ZnSe films were deposited by pulsed laser ablation on a crystalline GaAs substrate and on an amorphous quartz substrate. The deposition process was performed with the same growth parameters. The films were investigated by means of X-ray diffraction, reflectance and photoluminescence spectroscopy. The X-ray diffraction spectra have demonstrated that the films grow in a highly oriented way but having different orientations, i.e. the films deposited on GaAs grow (100)-oriented and the films deposited on quartz grow (111)-oriented. Reflectance spectra as a function of the temperature have been analysed by means of the classical oscillator model, in order to obtain the temperature dependence of the band gap energy. This gives results comparable to those of ZnSe single crystals for ZnSe on GaAs, but it is red-shifted for ZnSe on quartz, because of lattice and thermal strains. The photoluminescence measurements at T = 10 K confirm the better quality of ZnSe deposited on GaAs and show that pulsed laser ablation is a promising technique to grow films having intrinsic luminescence even on an amorphous substrate. Received 29 May 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: giuseppe.perna@ba.infn.it     

Synthesis, effect of capping agents, structural, optical and photoluminescence properties of ZnO nanoparticles

Zinc oxide nanoparticles were synthesized using chemical method in alcohol base. During synthesis three capping agents, i.e. triethanolamine (TEA), oleic acid and thioglycerol, were used and the effect of concentrations was analyzed for their effectiveness in limiting the particle growth. Thermal stability of ZnO nanoparticles prepared using TEA, oleic acid and thioglycerol capping agents, was studied using thermogravimetric analyzer (TGA). ZnO nanoparticles capped with TEA showed maximum weight loss. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for structural and morphological characterization of ZnO nanoparticles. Particle size was evaluated using effective mass approximation method from UV-vis spectroscopy and Scherrer's formula from XRD patterns. XRD analysis revealed single crystal ZnO nanoparticles of size 12-20 nm in case of TEA capping. TEA, oleic acid and thioglycerol capped synthesized ZnO nanoparticles were investigated at room temperature photoluminescence for three excitation wavelengths i.e. 304, 322 and 325 nm, showing strong peaks at about 471 nm when excited at 322 and 325 nm whereas strong peak was observed at 411 for 304 nm excitation.     

Epoxy ether cleaving reactions catalyzed by supporting Lewis acidic ionic liquid

Lewis acidic ionic liquids were used to catalyze the reaction of epoxypropane with POCl₃.Considering the lower cost and catalytic activities,we concluded that[Et₃NH]Cl/AlCl₃ was the most attractive ionic liquid from an economical point of view.But it would be easily inactivated because of sensitive to water and air.Moreover,it could not be reused easily because of difficulty recovery in the reaction.However,supporting[Et₃NH]Cl/AlCl₃ catalyst could resolve above problems.Supporting[Et₃NH]Cl/ AlCl₃ catalyst could be separated by filter easily and reused 5 times in 98%yield.Furthermore,the catalyst was applicable to other epoxy ether cleaving reactions.     

MgCl2/Et3N Base System as a New Catalyst for the Synthesis of α‐Hydroxyphosphonate

An efficient and simple synthesis of α‐hydroxyphosphonates via reaction of aldehydes and ketones with dimethylphosphite in the presence of MgCl₂/Et₃N base system is reported. The use of readily available and easy to handle reagent MgCl₂/Et₃N makes this method simple, convenient, and practical.     

使用DBDMH和Et3N·3HF的苯乙酮一锅法α-亲核氟代

报道一种通过溴代和氟代的一锅法操作,从苯乙酮直接制备α-氟代苯乙酮的新方法.使用1,3-二溴-5,5-二甲基海因(DBDMH)作为溴代试剂,三乙胺三氟化氢作为氟代试剂,除了p-和m-硝基苯乙酮之外,α-氟代苯乙酮以82%～87%的收率被获得.本方法使用的试剂价廉、收率较高、操作简单方便,有较高的应用价值.     

Application of Et3NHCl-AlCl3 Ionic Liquid as an Initiator in Cationic Copolymerization of 1, 3-Pentadiene with Styrene

Room temperature ionic liquids (RTILs) as advanced, technological solvents can be designed to fit a particular application. They used as green “media and/or catalysts” for chemical synthesis have been extensively reviewed recently. RTILs1 not only show …     

VOCl_3/Et_3Al_2Cl_3/CCl_4溶剂体系催化乙烯丙烯共聚

本文以VOCl_3/Et_3Al_2Cl_3为催化剂,在CCl_4溶剂中进行乙烯共聚反应。在聚合过程中,发生一异常的颜色突变现象。颜色突变后,体系催化聚合生成分子量很低的产物。从聚合物的结构表征及机理探讨表明:颜色突变后,体系产生了新的活性中心,催化机理发生了转变——由配位机理转变为阳离子机理。     

Phosphinophosphiniden-Phosphorane tBu2P?P = P(R)tBu2 aus Li(THF)2[η2-(tBu2P)2P] und Alkylhalogeniden

The Phosphinophosphinidene-phosphoranes ^tBu₂P? P = P(R)^tBu₂ from Li(THF)₂[η²-(^tBu₂P)₂P] and Alkyl Halides We report the formation of ^tBu₂P? P = P(R)^tBu₂ a and (^tBu₂)₂PR b (with R = Me, Et, ⁿPr, ⁱPr, ⁿBu, PhCH₂, H₂C = CH? CH₂ and CF₃) reactions of Li(THF)₂[η²-(^tBu₂P)₂P] 2 with MeCl, MeI, EtCl, EtBr, ⁿPrCl, ⁿPrBr, ⁱPrCl, ⁿBuBr, PhCH₂Cl, H₂C = CH? CH₂Cl or CF₃Br. In THF solutions the ylidic compounds a predominate, whereas in pentane the corresponding triphosphanes b are preferrably formed. With ClCH₂? CH = CH₂ only b is produced; CF₃Br however yields both ^tBu₂P? P = P(Br)^tBu₂ and ^tBu₂P? P = P(CF₃)^tBu₂, but no b . The ratio of a:b is influenced by the reaction temperature, too. The compounds ^tBu₂P? P = P(Et)^tBu₂ 4a and (^tBu₂P)₂PEt 4 b , e. g., are produced in a ratio of 4:3 at ?70°C in THF, and 1:1 at 20°C; whereas 1:1 is obtained at ?70°C in pentane, and 1:2 at 20°C. Neither ^tBuCl nor H₂C = CHCl react with 2 . The compounds a decompose thermally or under UV irradiation forming ^tBu₂PR and the cyclophosphanes (^tBu₂P)_nP_n.