CW coherent VUV radiation generated by resonant sum-frequency mixing in metal vapors

Resonant third-order sum-frequency mixing of continuous-wave visible and ultraviolet laser light is investigated in the metal vapors of Sr, Ca, Mg, and Zn. The laser radiation (with the frequencies ₁, ₂, and ₃) is generated by single-mode dye- and argonion lasers. The third-order nonlinear susceptibility is enhanced by tuning the laser frequencies 2₁ or ₁+₂ to a two-photon resonance. The wavelength of the generated coherent VUV radiation (with the frequency _VUV=3₁, _VUV=2₁+₂ or _VUV=₁+₂+₃) is tunable in spectral regions between 133 and 217 nm. For most conversion processes an additional enhancement of the nonlinearity is provided by an autoionizing level or by a highly excited state close to E=_VUV. With laser powers of 0.2–3 W the power of the generated sum frequencies is in the range of 5×10⁵–6×10¹⁰ photons s^–1 (0.5 pW–60 nW).     

激光散射法测试超细颗粒粒度分布的研究

本文系统研究了样品制备条件对激光散射法测试超细颗粒粒度的影响,例如:分散介质的选择、分散剂的类型和浓度、分散颗粒的浓度、超声分散的时间和强度等。并与其他TEM结果进行了对比。研究表明:只有将各种条件最优化,获得高度分散和稳定的悬浮体系或胶体体系,才能最终精确地得到颗粒的粒度分布结果。     

CdS半导体超微粒样品光谱性质的研究

纳米尺度的半导体超微粒在线性和非线性光学方面表现出来的奇特性质使其成为研究和开发新的功能材料的热点。成键为 S、P轨道的 - 族金属硫化物半导体 ,电子结构和晶体结构均较为简单 ,结晶性能好 -界面无序结构少 ,在纳米尺度上其结构仍与体相材料近似 ,因此 ,成为研究量子尺寸效应的理想材料。本文对采用化学微乳液法合成的 Cd S半导体超微粒的光谱性质进行了研究 ,实验结果显示 ,Cd S超微粒样品的吸收光谱的带边与体相相比发生了蓝移 ;从吸收光谱中可以看到 ,Cd S超微粒样品的吸收边随粒径减少而向短波方向移动。拉曼光谱的电子—— L O声子耦合在粒子尺寸 2 .4- 2 .9nm范围内与粒子尺寸无关     

Simulation of Dynamic Light Scattering Signals of Ultrafine Particles

In order to conveniently obtain dynamic light scattering (DLS) signal, a simulation method of DLS signal is proposed in this paper. This method regards the light intensity fluctuation of DLS as a stationary random process. According to autocorrelation function (ACF) of DLS signal, the stationary random process of DLS can be generated by auto‐regressive (AR) model. Signal simulations of several kinds of distribution particles and comparison of simulations and experiment prove that AR model can be used for DLS signal simulation. Moreover, by analyzing effect of simulation parameters on simulation precision, we obtained the relationship between simulation parameters and simulation precision. Finally, application of simulation signal verifies the effectiveness and convenience of this simulation method.     

Lasers based on vapors of complex organic compounds

The properties of the emission of lasers based on complex organic compounds, in the quasistationary lasing regime, are theoretically investigated with allowance for the induced losses in the spectral lasing region in the system of triplet and excited singlet states of the molecules. The results of the calculations are compared with the experimental data for lasers using POPOP and TOPOT vapors. The thermal endurance of these compounds at T < 600OlaggyK is investigated, the constants of the singlet-triplet conversion and the cross sections for the absorption of the excited singlet molecules TOPOT in the lasing band are determined, and the effectiveness of stabilizing the POPOP and TOPOT vapors by a buffer gas is estimated.The paper contains results of calculations and experiments included in the candidate's dissertation of K. K. Trusov, Investigation of lasers based on vapors of complex organic compounds, Moscow, Physics Institute of the Academy of Sciences, 1978).Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Akademii Nauk SSSR, Vol. 125, pp. 20–45, 1980.     

Crystal Phases of TiO2 Ultrafine Particles Prepared by Laser Ablation of Solid Rods

Titanium dioxide ultrafine particles (UFPs) are produced by pulsed laser ablation of titanium or titanium dioxide (anatase and rutile) rods in an atmosphere of He or O₂/He mixture. The collected UFPs on cellulose membrane filters at the exit of the ablation chamber are analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TiO₂ particles produced are composed of very small particles (diameter: 10–50nm) that are completely anatase, irrespective of the rod material, and relatively large particles (diameter: 100nm–1m) that are a mixture of anatase and rutile. The large particles consist of the direct strip-off fragments coming from the rod surface. The particles obtained from the laser ablation on TiO₂ rods in an atmosphere of He contains gray particles that are supposed to be amorphous TiO₂ (x < 2). In the presence of O₂ in the ablation chamber, these oxygen defects in amorphous TiO₂ are stabilized and anatase UFPs are formed. These results suggest that the crystal phase of the products can be controlled by adjusting the rod material and the gases used in the ablation process.     

发射光谱研究多针对板电晕放电O活性原子特性

利用发射光谱技术在大气压下测量了空气中多针对板负直流电晕放电和正电晕流光放电产生的O(3p5 P→3s 5 S02777.4nm)活性原子发射光谱。在负电晕放电中,研究了放电功率、电极间距、N2含量和相对湿度等因素对O活性原子产生过程的影响;在正电晕流光放电阶段,研究了O活性原子相对密度在放电反应空间的分布特点。结果表明:O活性原子产量随放电功率的增加而增大,随电极间距增大而减少,随相对湿度和氮气含量的增加,其产量先增大后减少;O活性原子相对密度沿针尖轴向呈先增大后减小的趋势。     

Nonlinear susceptibilities of vapors and solutions of organic dyes

Results of theoretical studies of laser and Kerr nonlinear susceptibilities of vapors and solutions of organic dyes using a series of polycyclic arenes as an example are presented. Nonlinear susceptibilities of the third χ⁽³⁾ (?3ω; ω, ω, ω) and the fifth χ⁽⁵⁾ (?3ω; ω, ω, ω, ω, ?ω) orders of a series of organic dyes responsible for third harmonic generation of Nd:YAG laser radiation are calculated within the context of the free electron model. Results of calculations of their Kerr third-order nonlinear susceptibilities χ⁽³⁾ (?ω; ω, ?ω, ω) and non-linear refractive indices n ₂ are presented. The calculation results are compared with experimental data on third harmonic generation in naphthalene vapors and with χ⁽³⁾ (?ω; ω, ?ω, ω) as well as n ₂ of paraterphenyl and naphthalene solutions.     

Quantum efficiency and thermal stability of organic dye vapors

Organic dyes, POPOP, perylene and pyren, in the vapor phase are excited by a N₂ laser. The quantum efficiency is measures as a function of temperature up to 450°C. Optical properties such as the radiative transition probability are also estimated from the experimental results. It is found that the decrease in the vapor density by the thermal dissociation can be neglected during several tens of hours.     

Preparation of Ultrafine Colloidal Gold Particles using a Bioactive Molecule

Synthesis of nanometer-sized particles with new physical properties is an area of tremendous interest. In metal particles, the changes in size modify the electron density in the particles, which shifts the plasmon band. The most significant size effects occur when the particles are ultrafine (size is <10 nm). Thus the synthesis of ultrafine metal particles is enormously important to exploit their unique and selective application. Here we report a novel method for the synthesis of ultrafine gold particles in the size range of 0.5–3 nm using dopamine hydrochloride (dhc), an important neurotransmitter. This is the first time where such an important bioactive molecule like dhc has been used as a reagent for the transformation of Au(III) to Au(0). The synthesis is carried out, for the first time, either in simple aqueous or in a nonionic micellar (for example Triton X-100 (TX-100)) medium. The gold sol has a beautiful yellow–brown color showing _max at 470 nm. The appearance of the absorption peak at substantially shorter wavelength (usually gold sol absorbs at 520 nm) indicates that the particles are very small. The method discussed here is very simple, reproducible and does not involve any reagent, which contains 'P' or 'S' atoms. Also in this case no polymer or dendrimer or thiol-related stabilizer is used. The effects of different parameters (such as the presence or absence of O₂, temperature, TX-100 concentration and dhc concentration) on the formation of ultrafine gold particles are discussed. The effects of 3-mercapto propionic acid and pyridine on the ultrafine gold sol are also studied and compared with those on photochemically prepared gold sol. It is observed that 3-mercapto propionic acid dampens the plasmon absorption at 470 nm of ultrafine gold particles. Pyridine, on the other hand, has no effect on the particles.     

多针对板负电晕放电激发态N原子发射光谱研究

在常压空气中,利用OES技术检测到负直流电晕放电等离子中激发态N原子发射光谱,并利用相对谱峰强度最大的674.5nm N原子激发跃迁谱线研究了相关空气参数和电参数对其相对密度的影响。结果表明,电离区内N原子相对密度随注入功率的升高呈增加趋势;随电极间距和相对湿度的增加,其相对密度逐渐减小;随N2流量增加,其相对密度呈先增加再减小趋势。在实验条件下,当针尖轴向距离r=1mm时,N原子相对密度出现最大值。     

超微镍粒子/聚苯胺纳米复合材料制备及其表征

反相微乳液法 (inversemicroemulsionsystems ,W /O型 )是制备纳米复合材料有效而简单的液相化学制备方法[1,2 ] .本工作首次采用两步连续反相微乳液法原位聚合制备超微镍粒子 (Ni) /聚苯胺 (PANI)纳米复合材料 .首先 ,利用无机化合物之间的氧化还原反应 ,将十二烷基苯磺酸钠 (DBS)和NiCl2 溶液按一定比例加入锥形瓶中 ,再加入异戊醇和正庚烷混合溶剂 ,常温下电磁力搅拌 ,体系变得半透明 (淡黄色 )形成微乳溶液 (W /O型 )称为 (A) ;然后再配制DBS和NaBH4 与异戊醇和正庚烷混合溶剂 ,形成微乳溶液 (W /O型 )称为 (B) ;两步连续反相…     

Triplet-triplet transfer of electronic excitation energy in vapors of organic molecules

The rate constants of the triplet-triplet (T-T) transfer of energy of the electronic excitation obtained in the gas phase for two sets of donor-acceptor pairs with various spectral characteristics are compared with those predicted by the theories of nonradiative transitions. The rate constants K _TT and efficiencies β_DA of the T-T transfer are estimated from quenching of the phosphorescence of biacetyl by aromatic hydrocarbons (anthracene, 9-methylanthracene, 9,10-dimethylanthracene, 9-phenylanthracene, pyrene, and chrysene) and from quenching of the delayed fluorescence of benzophenone, 4-phenylbenzophenone, anthraquinone, carbazole, and naphthalene by biacetyl, as well as from the sensitization of phosphorescence of biacetyl by these compounds. The causes of the broad variations of β_DA in the gas phase from 0.35 (biacetyl-anthracene) to 10^?4 (biacetyl-chrysene) are discussed for the studied donor-acceptor pairs, which differ in the exothermicity of the process and in the configuration of the lowest triplet levels of the molecules participating in the transfer. The dependences of the transfer rate constants K _TT on the free energy change ΔG (the range from 0.4 to ?1.7 eV) are analyzed. It is shown that, in gas-phase systems, K _TT increase with the exothermicity of the transfer, attain a highest value, and then decrease in the range of negative ?ΔG. The observed differences in the experimental values of β_DA are discussed in terms of changes in the free energy ΔG of the process, in the energy of rearrangement of the nuclear configuration of the molecules during the transfer, and in the matrix elements of the interaction.     

双峰分布的超细颗粒动态光散射信号模拟及精度分析

为获取双峰分布超细颗粒的动态光散射模拟信号,通过建立动态光散射随机过程的AR模型,利用修正的Levison Durbin递推算法确定模型参数和阶数的方法模拟光散射信号.分别对10 nm与90 nm,200 nm与1 000 nm双峰分布颗粒的动态光散射信号进行模拟,得到的模拟信号光强自相关函数与理论值吻合,用双指数法对颗粒粒径反演,相对误差小于3.55%.通过分析模型阶数、采样时间、采样频率、模拟数据长度等参数对模拟精度的影响,得出双峰分布颗粒光散射信号的模拟精度与各参数的关系:在低于阈值阶数时,模型阶数选择对精度影响大,模型阶数越高,信号模拟的精度越高,高于阈值阶数时,模型阶数选择对精度影响不大,可选阈值阶数模型模拟信号.选定一定的采样时间,采样频率越高,模拟数据长度越长,模拟精度越高.