Special features of electron beam-excited XeCl-laser generation

The results of experimental investigations on generation in Ar(Ne): Xe: CCl₄(HCl) mixtures at excitation by an electron beam are given. It is shown that the use of CCl₄ and HCl with an Ar buffer gas gives equal radiative energies and efficiencies and ā change of Ne for Ar causes a change in generation spectrum. The special features of XeCl-laser generation are discussed.     

Transient stimulated Raman scattering in a two-component gas mixture

Generation of the first Stokes components of stimulated Raman scattering (SRS) in two-component gas mixtures, including the combination component (resulting from scattering of the first (second) Stokes component in the second (first) gas) is studied by numerical methods. The condition for efficient generation of the combination Stokes component is derived and interpreted. It is shown theoretically and by numerical simulation that the optimal ratio of the pressures for the transient SRS generation of the combination component is inversely proportional to the ratio of the Raman scattering cross sections of the two gases. The results of numerical simulation agree well with experimental data.     

Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems,Part I: H2O2 generation

Cavitational/sonochemical activity can be significantly enhanced or reduced depending on the gases dissolved in the liquid. Although many researchers have suggested the order of importance of dissolved gas conditions that affect the degree of sonoluminescence (SL), sonochemiluminescence (SCL), and compound degradation, the most suitable gas condition for sonochemical oxidation reactions is currently unknown. In this study (Part I), the effects of gas saturation and sparging on the generation of H₂O₂ were investigated in a 28-kHz sonoreactor system. Four gas modes, saturation/closed, saturation/open, sparging/closed, and sparging/open, were applied to Ar, O₂, N₂, and binary gas mixtures. The change in dissolved oxygen (DO) concentration during ultrasonic irradiation was measured and was used as an indicator of whether the gaseous exchange between liquid and air altered the gas content of the liquid. Considerable difference in the DO concentration was observed for the gas saturation/open mode, ranging from –11.5 mg/L (O₂ 100 %) to +4.3 mg/L (N₂ 100 %), while no significant difference was observed in the other gas modes. The change in the gas content significantly reduced the linearity for H₂O₂ generation, which followed pseudo-zero-order kinetics, and either positively or negatively affected H₂O₂ generation. Ar:O₂ (75:25) and Ar:O₂ (50:50) resulted in the highest and second-highest H₂O₂ generation for both gas saturation and sparging, respectively. In addition, gas sparging resulted in much higher H₂O₂ generation for all gas conditions compared to gas saturation; this was because of the significant change in the cavitational active zone and concentrated ultrasonic energy, which formed a bulb-shaped active zone, especially for the Ar/O₂ mixtures adjacent to the transducer at the bottom. The sparging flow rate and position also significantly affected H₂O₂ generation; the highest H₂O₂ generation was obtained when the sparger was placed at the bottom adjacent to the transducer, with a flow rate of 3 L/min.In Part II, the generation of nitrogen oxides, including nitrite (NO₂^–) and nitrate (NO₃^–), was investigated using the same ultrasonic system with three gas modes: saturation/open, saturation/closed, and sparging/closed.     

Transient stimulated Raman scattering in gas mixtures

We studied, for the first time to our knowledge, transient stimulated Raman scattering in H(2)- D(2) and H(2)- CH(4) gas mixtures excited with 200-fs and 2-ps, 390-nm pulses. Depending on the composition and partial pressure, of those gases, we observed ~40 output lines simultaneously. Under optimum conditions a conversion efficiency of as much as 8% in the combination Raman line at 556 nm was obtained in the H(2)- CH(4) gas mixtures. The difference between picosecond and femtosecond pumping is due to self-phase modulation and to generation of a spectral continuum in the latter. Our calculation of the ratio of the partial pressures is in a good agreement with the experimental results. A new method for measuring the unknown Raman scattering cross section of gas molecules is suggested.     

HeKr laser with transverse hollow cathode discharge

Quasi-CW laser generation on five KrII lines in HeKr gas mixtures is observed using sectioned hollow cathode construction in which transverse discharge is realized. Gain of 19%/m and output power of 34 mW are achieved. Single longitudinal mode operation is obtained.     

直流场畸变开关中混合气体击穿特性

氩气中一般含有大量亚稳态原子,在强外电场作用下容易产生自由电子,能够促进放电通道快速形成。采用场畸变型气体开关,在直流电压下设计了实验平台来探究气体开关中采用SF6-Ar或N2-Ar混合气体后放电时延及抖动的变化情况。改变多种气体状态进行一系列实验,并得出场畸变气体火花开关中SF6-Ar及N2-Ar的击穿特性,根据工程需要对气体种类及混合比例进行最优化设计。实验表明SF6-Ar中Ar质量分数达到20%及以上时,开关放电时延及抖动明显减小。     

新型涡旋多相泵原理及其工作过程研究

提出了一种新型涡旋式气液多相混输泵,通过构建变啮合间隙涡旋齿型线,使得所形成的压缩腔存在一条通向排出口的内泄漏卸压通道。构建了一种液相压缩卸荷的新方法,解决了容积式多相泵在混输较高含液率介质时易出现的压缩腔液击问题。介绍了新型涡旋多相泵的工作原理,得到了变啮合间隙涡旋齿型线的生成方法和型线方程,分析了工作腔容积和啮合间隙的变化规律。建立了涡旋多相泵工作过程中气液介质在伴有内泄漏时的增压过程热力模型,求解得到了工作过程中压力的变化规律。     

Energy relaxation time in a gas mixture measured by a photothermal probe beam deflection technique

The deflection of a cw probe laser beam, which occurs in a gas mixture after the absorption of a short laser pump pulse, was experimentally studied inside the irradiated region in order to characterize the generation of photothermal and photoacoustic effects. The time varying component of the probe deflection was detected, and the results are presented as functions of pumping fluences, laser wavelengths and gas pressures. Numerical modelling of the thermo-acoustic dynamics leads to the definition of an effective energy relaxation time for SF₆/Ar gas mixtures. An interesting nonlinear behaviour of this energy relaxation time is reported.     

电激励O2（a1Δg）发生器的实验研究

 在纯氧，及氧气和氩气的混合气体情况下，对射频放电产生O₂（a¹Δg）进行了实验研究。射频频率为13.56MHz，额定功率500W，放电压力133.0~399.0Pa， 氧气流量最大为1.4mmol/s， 氩气流量为2.1mmol/s。研究了O₂（a¹Δg）产率随气体流量、放电气压以及混合气体放电条件的变化。O₂（a¹Δg）产率最大值约为17.5%。     

Destructive interference of laser harmonics in mixtures of various emitters in plasma plumes

We analyzed the interference of two high-order harmonic generation processes in mixtures of different materials. These studies were carried out using mixtures of silver and gold nanoparticle suspensions, as well as mixtures of boron and carbon. These samples were ablated using picosecond pulses and probed by femtosecond pulses. While the harmonic cutoffs remained approximately the same for the mixtures and the separate ingredients, the conversion efficiency in the case of plasma plumes containing the mixtures of the above materials noticeably decreased around all spectral ranges of harmonic generation. These studies show that destructive interference in these media dominates over constructive interference.     

Experimental investigations and modelling studies of ozone producing corona discharges

The ozone generation by negative corona discharge in coaxial cylindrical system of electrodes have been studied experimentally in Ar+O₂ and N₂+O₂ mixtures. Both in argon and nitrogen mixtures with oxygen the monotonous decrease in ozone concentration [O₃] was observed at decreasing oxygen content in mixtures and the constant input energy density η. The rate coefficients for the ozone generation and ozone decomposition were obtained by fitting experimentally measured data [O₃]=f(η) with Vasiljev-Eremin formula. The calculated rate coefficient for ozone generation in N₂+O₂ mixtures at low content of oxygen (below 20%) was found considerably higher than that in Ar+O₂ mixtures. Increase in the rate coefficients for ozone generation and decomposition was observed with decreasing content of oxygen in both mixtures. The experimental results are in qualitative agreement with the simple model incorporating five main chemical processes in mechanism of ozone generation. The research was partially supported by Slovak Grant Agency under project 1/765920 The UK EPSRC (Grant GM/98944) and NATO Joint Project PST CLG 976544.     

Interruption Capability of Gases and Gas Mixtures in a Puffer-Type Interrupter

SF6 gas has been widely used in arc interruption applications for the past 20 years. Reported here is a systematic, comprehensive effort to search for and evaluate gases and gas mixtures suitable as an arc interruption medium potentially superior to SF6. The search began with several hundred gases, narrowed down to about forty, and finally fifteen gases and gas mixtures were evaluated in a full size puffer-type interrupter under 60-Hz high-power conditions. The results showed SF6 stood out as having the best interruption ability with several mixtures having ~80 percent of SF6' s performance.     

电负性混合气体临界电场强度的确定

本文讨论了确定电负性混合气体临界电场强度的两种方法。一是用电负性混合气体中各组成气体的预放电参数来确定按任意比例混合的气体之临界电场强度。另一是由高能脉冲激光释放电子,记录预放电电子电流波形来确定混合气体的临界电场强度。用这两种方法确定N₂和SF₆混合气体的临界电场强度,其结果十分符合。 关键词：     

多原子分子气体中声波弛豫衰减谱的重建算法

提出了一种宽频率范围的弛豫衰减谱重建算法,并采用基于SSH理论的方法和基于实验数据的方法估计气体的有效弛豫时间.通过该算法得到了包括氮气、甲烷、氧气、二氧化碳和水蒸气在内的多种多原子分子混合气体的声衰减谱,研究的声波频率范围从1Hz到10GHz.与预测弛豫衰减的DL模型的结果比较表明,该算法获得的弛豫衰减谱结果与之相符,其预测精度取决于对分子弛豫过程的正确认识.另外该算法还被用于几种混合气体中水蒸气和二氧化碳含量的分析,其结果表明弛豫衰减谱可被用于定量分析多原子分子气体的成分组成,这使得实现高灵敏度地检测气体成分的智能声气体传感技术成为可能. 关键词： 声弛豫衰减 有效弛豫时间 重建算法 声气体传感器     

Molecular relaxation effects in hydrogen chloride photoacoustic detection

A photoacoustic (PA) sensor has been developed to monitor hydrogen chloride at sub-ppm level in the 1740-nm region. The system was designed to control the process in the novel low-water-peak optical fiber manufacturing process. Relaxation effects in hydrogen chloride PA detection in oxygen–helium and nitrogen–helium gas mixtures are presented, showing that the generation of the PA signal is strongly affected by the ratio of these substances. In addition, the role of water vapor in the PA signal is investigated.     

Quantitative gas measurements using a versatile OPO-based cavity ringdown spectrometer and the comparison with spectroscopic databases

A versatile OPO-based cavity ringdown spectrometer is reported for quantitative and sensitive gas measurement down to nmol/mol levels. The system is based on cavity ringdown spectroscopy (CRDS) in combination with a continuous wave optical parametric oscillator tunable from 2693 to 3505 nm. Using a single set of CRDS mirrors, spectra were recorded of methane, ethane, benzene, propane, water, acetone and formaldehyde. Gas mixtures were gravimetrically prepared in cylinders or via dynamic generation using diffusion tubes (formaldehyde). Results were compared with data from the Hitran, PNNL and NIST databases. Good agreement was found with PNNL and NIST data for most molecules while agreement with Hitran was less for ethane and formaldehyde.     

Hydrogen adsorption and absorption on evaporated Nb films: Study by measurements of work function changes

The field ionization of He-Ne, He-A, He-Kr, He-Xe and Ne-A gas mixtures is investigated. Only for the first three gas mixtures mentioned, an increased ionization rate (image promotion) is observed. The influence of field adsorbed neon on the image contrast in a helium field ion microscope is described. The best image voltage (BIV) for a He-Ne mixture corresponds to a minimum in image contrast. Furthermore, a number of rules governing the field ionization of rare gas mixtures are stated.     

Spectroscopic diagnostics of barrier discharge plasmas in mixtures of zinc diiodide with inert gases

The spectral characteristics of the emission of gas discharge atmospheric pressure plasmas in mixtures of zinc diiodide vapor with inert gases (He, Ne, Ar, Kr, and Xe) are investigated. The formation of a gas discharge plasma and the excitation of the components of a working mixture were performed in a high-frequency (with a repetition frequency of sinusoidal voltage pulses of 100 kHz) barrier discharge. The gas discharge emission was analyzed in the spectral range 200–900 nm with a resolution of 0.05 nm. Emission bands of ZnI(B-X) exciplex molecules and I₂* excimer molecules, lines of inert gases, and emission bands of XeI* exciplex molecules (in Xe-containing mixtures) were revealed. It is ascertained that the strongest emission of ZnI* molecules is observed in ZnI₂/He(Ne) mixtures. The regularities in the spectral characteristics of the gas discharge plasma emission are considered.     

Products of carbon disulfide oxidation in ionized air

Products of plasmochemical reactions proceeding in gas mixtures containing toxic CS₂ impurity were studied. The mixtures were excited by 180-and 300-keV electron pulses of duration 3 ns and 48 μs, respectively.     

Numerical simulation of nonlinear acoustic attenuation of multi-component gas mixture

The direct simulation Monte Carlo （DSMC） method was introduced to model the acoustic propagation in multi-component gas mixtures. And a theoretical predictive model of acoustic attenuation was proposed, which does not rely on experiential parameters. The acoustic attenuation spectra of various multi-component gas mixtures, consisting of nitrogen, oxygen, carbon dioxide, methane and water, were estimated by the DSMC method. The sound frequency range of interest is from 8 MHz to 232 MHz. Compared with the result of the relaxation attenuation based on the DL model plus that of the classical attenuation calculated by the Stokes-Kirchhoff formula, the estimations of acoustic attenuation of our model agreed with them. The precision of the model depends upon the understanding of the physical mechanism of molecule collision from which the attenuation arises. In addition, the result of our model shows that the characters of the frequency-dependent acoustic attenuation rely on the composition of the gas mixtures. And this could lead to the development of smart acoustic gas sensors capable of quantitatively determining gas composition in various environments and processes.