Pulsed CO2 laser-induced gas plasma spectroscopy based on single beam splitting for trace metal analysis on a material surface

Laser-induced gas plasma spectroscopy based on pulsed CO₂ laser beam splitting has been applied to the problem of trace film analysis on the silicon surface. In this study, 2.1?J of laser energy (70% of the laser beam) was focused at a 10-degree incidence on a metal mesh attached to a sample surface containing trace metal elements in order to produce a gas plasma. The remaining part of the laser beam (approximately 30% or 0.9?J) was employed to vaporize a film which had been deposited on the material by focusing the laser beam 3?cm under the surface. In this scheme, the vaporized metal film moves into the gas plasma region, in which the dissociation and excitation takes place. Our measurements show that the detection of Cr on the silicon surface can be made with high sensitivity. The limit of detection of Cr in the silicon material was approximately 7.5?×?10¹²?atom/cm².     

Characteristics of laser-induced plasma from highT c superconductor

The spectroscopic analysis of the emission from the plasma produced by irradiating a highT _c superconducting GdBa₂Cu₃O₇ target with a high power Nd:YAG laser beam shows the existence of the bands from different oxides in addition to the lines from neutrals and ions of the constituent elements. The spectral emissions by oxide species in laser-induced plasma show considerable time delays as compared to those from neutral and ionic species. Recombination processes taking place during the cooling of the hot plasma, rather than the plasma expansion velocities, have been found to be responsible for the observed time delays in this case. The decays of emission intensities from various species are found to be non-exponential.     

离焦量对空气中YAG激光诱导Cu等离子体空间特性的影响

利用Nd:YAG脉冲激光在空气中烧蚀Cu靶,产生激光等离子体羽,通过改变离焦量获得相应的等离子体的空间谱;用光谱学方法分析了三种离焦量下空间谱线结构和空间等离子体的电子温度演化规律;并对等离子体光谱的特性和产生机制进行了讨论.结果表明:离焦量对等离子体的谱线强度、谱线结构、电子温度的空间特性都有影响,特征谱强度最大值出现在空间位置1.0mm附近,离焦量为-2mm时电子温度最高.     

In-situ optical emission spectroscopy of laser-induced vanadium oxide plasma in vacuum

This study aims to analyze the elemental composition, and temporal- and spatial distributions of vanadium atoms and ions in the laser-induced vanadium oxide plasma under high vacuum using optical emission spectroscopy. Neutral atoms and singly charged V ions were detected under high vacuum in the emission spectra. The mean translational velocity of neutral V atoms in their first 25 mm propagation was estimated to be 15.7 km/s using the temporal- and spatial dynamics investigation of neutral V species in the plasma.     

Sensitivity enhancement of laser absorption spectroscopy for atomic oxygen measurement in microwave air plasma

A high sensitive laser absorption spectroscopy system has been developed for the detection of atomic oxygen in a microwave plasma. Firstly, the sensitivity of this system was evaluated by ring-down time measurement. The effective absorbing pass length was extended up to 640 times as long as that of the conventional laser absorption spectroscopy. Then, the system was applied to the air plasma diagnostics. As a result, the absorption signal from the meta-stable atomic oxygen at 777.19 nm could be observed at the input enthalpy range from 0.93 MJ/kg to 467 MJ/kg. The detected minimum number density was 1.6 × 10¹¹ m⁻³ with temperature of 388 K, which correspond to the center fractional absorption of 1.4 × 10⁻²% in the LAS.     

真空环境下指数脉冲放电等离子体特性分析

真空环境内金属电极放电产生的等离子体不同于气体放电等离子体,具有特殊的性质.本实验采用持续时间为10μs,幅值约600A的指数变化的脉冲电源进行放电;运用朗缪尔探针法对放电生成的等离子体的相关参数进行测量,讨论了放电生成的等离子体的特性,分析了电极间距对放电等离子体密度的影响;同时运用AnsoftMaxwell3D仿真软件对电极间的电场分布情况进行了仿真分析.实验发现采用指数脉冲放电能生成高密度的等离子体,且生成的等离子体密度随电极间距增大而增大.     

Effect of the electrode material on the atmospheric plasma conversion of NO in air mixtures

Non-thermal atmospheric pressure plasma is widely used for conversion of hazardous gases. Results from different laboratories confirm importance of energy non-equilibrium in the plasma where dominant energy carriers are electrons and a dominant chemistry is based on formation and interactions of radicals. Because of rather high electric fields required for generation and sustaining of air discharges at atmospheric pressure many plasma systems were found rather to create a lot of NO instead of removing it. A widely supported way to clean NO and NO₂ from air mixtures is a plasma assisted catalytic reduction where the cold plasma is combined with the solid-state catalyst. In an ideal case the plasma acts as an oxidation catalyst where an atomic oxygen from air oxidizes NO to NO₂ and the solid-state catalysts are then capable to convert all NO₂ to N₂ and O₂. In most cases it is also necessary to involve auxiliary gases, e.g., propylene, to make the process efficient enough. This work introduces an original cold plasma system based on atmospheric hollow cathodes generated by a nanopulse DC power with controllable voltage and pulse frequency. The system was optimized in both the geometry and the applied power. However, the material of electrodes was found to be the most important factor affecting the plasma performance and consequently the chemical kinetics. A 100% conversion of NO to NO₂ was achieved with a graphite electrode, without using any auxiliary gas and without catalyst. Plasma performance and conversion efficiency are compared for several electrode materials.     

Investigation of gas-liquid interface in atmospheric-pressure micro plasma with solution

An atmospheric-pressure glow-discharge micro plasma in contact with liquid paraffin is stably generated by using a capacitively coupled plasma method with a mesh electrode. When characteristics of the plasma are measured in the boundary between the micro plasma (gas-phase) and liquid paraffin (liquid-phase) using optical emission spectroscopy, spectrum peaks of the emission of CH and C₂ which dissociate from paraffin are observed. The result indicates that solution can feed particles to the plasma at gas-liquid interface and this plasma is accordingly expected to promote an attractive plasma process for creating materials consisting of elements in various solutions.     

氢化物发生电感耦合等离子体发射光谱法测定钢中微量砷

该文研究氢化物发生-电感耦合等离子体发射光谱法测定非合金钢(碳素钢)和低合金钢中微量砷的分析方法,考察高频功率、雾化压力、辅助气流量、泵速等仪器工作条件与消解用酸及用量、硼氢化钠浓度对光谱强度的影响,并讨论王水、铁基体、共存离子对测定结果的背景干扰与消除方法.确定的最佳工作条件为:高频功率为1350 W,雾化压力为22...     

Evolution of the polarization state for radiation propagating in a nonuniform, birefringent, optically active, and dichroic medium: the case of a magnetized plasma

First, the analytic expressions are derived that describe some properties of the Poincaré sphere that are related to the coherent sum of two waves having different polarizations. Then these expressions are used to obtain the differential equation that describes the evolution of the state of polarization of radiation propagating in a medium that is nonuniform, birefringent, optically active, and dichroic. Finally, an important example is presented: that of a magnetized plasma in which particle collisions are not negligible, such as the earth's ionosphere or certain laboratory plasmas. The evolution equation is the basis of plasma polarimetry.     

Synthesis of SiC from rice husk in a plasma reactor

A new route for production of SiC from rice husk is reported by employing thermal plasma technique. The formation of β-SiC is observed in a short time of 5 min. The samples are characterized by XRD and SEM.     

Effect of self-generated axial magnetic field and on propagation of intense laser radiation in plasmas

The present paper deals with an analytical study of a self-generated axial magnetic field (SGAMF) through the inverse Faraday effect (IFE) and its influence on the propagation of circularly polarized light wave for relativistic intensities. As a first step, the non-linear dielectric constant incorporating a magnetic field in the relativistic factor within the framework of WKB (for Wentzel, Kramers, and Brillouin) and a paraxial ray theory is formulated. It is noticed that for intensities (>10¹⁸ W cm^?2), circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density as well as a strong flow of relativistic electrons, axially co-moving with the pulse rise. The above generates a magnetic field up to 100 MG and strongly influences the light propagation. Two modes of propagation exist, namely, extraordinary and ordinary, and critical power for focusing is different for the two modes. The non-linear dielectric tensor, propagation equation, and the self-trapped radius are evaluated incorporating an induced magnetic field. The focusing conditions strongly depend on the power of the beam, strength of the magnetic field as well as on the density of the medium. Numerical calculations are made for a typical set of relativistic laser plasma interaction processes.     

Spectral shifts and spectral switches of a pulsed Gaussian beam from a rectangular aperture in the far field

The far-field anomalous spectral behaviours of a space–time-dependent Gaussian pulsed beam passing through a rectangular aperture are studied. By expanding a hard aperture function into a finite sum of complex Gaussian functions and starting from the Fresnel diffraction integral, the approximate analytical expression for the spectral intensity of a space–time-dependent Gaussian pulsed beam passing through a rectangular aperture is derived. Meanwhile, the corresponding closed-forms for the slit and the unapertured cases are also given as special cases of the general results. The red and blue shifts and the spectral intensity distribution are studied and illustrated with numerical calculations. Specifically, it is shown that the spectral switch takes place when the truncation parameter is equal to particular values or the observation position is at the critical diffraction angle. The possibility of tunable spectral switching in the far field with an apertured pulsed beam by varying the size of the rectangular aperture is highlighted.     

Effects of VUV/UV radiation and oxygen radicals on low-temperature sterilization in surface-wave excited O2 plasma

Effects of VUV/UV radiation and oxygen radicals on low-temperature sterilization in surface-wave excited O₂ plasma were studied. To examine the effect of VUV/UV radiation on the inactivation of microorganisms, a small metal chamber covered with an optical filter at the top to block the radicals and allow the VUV/UV radiation was placed inside the plasma chamber. With a LiF and a glass filter, two different emission spectra above 120 nm (LiF filter) and above 300 nm (glass filter) were examined. The spores of Geobacillus stearothermophilus with a population of 2.5 × 10⁶ were put below the optical filter in the small chamber, which was filled with the oxygen gas at appropriate pressure or pumped down to 10^− 3 Pa. The survival curve showed that the vacuum condition inside a small chamber with a LiF filter was more efficient than the same O₂ gas pressure as that outside plasma chamber. From the SEM analysis of the spores, there was no obvious change in shape after plasma treatment with filter at vacuum condition. According to the present results, it is concluded that the etching effect by the oxygen radical is more efficient in inactivation process than the sterilizing effect by the VUV emission in the oxygen plasma.     

Determination of the acoustic pressure in a liquid from the parameters of passing laser radiation

Using a mathematical model of the propagation of a laser beam in an acoustic field, the distortions of the envelopes of the beam intensity due to refractive convergence and divergence of the rays in the beam are calculated. Experimental equipment is constructed and measurements of the acoustic pressure in a liquid are made. The experimental results obtained agree with the theoretical conclusions. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 53–55, June, 2006.     

Investigation of Ti coatings on cubic boron nitride (cBN) grits by discharge treatment in spark plasma sintering system

The Ti coatings on cubic boron nitride (cBN) grits were prepared by discharge treatment on a mixture of Ti powders and cBN grits in spark plasma sintering system. The uniform and full coatings with a thickness of ～1.2 μm were prepared at 850 °C for 60 min, which were constituted with TiB₂, TiN, and Ti phases. The compressive fracture strength and toughness impact of the Ti-coated cBN grits were 11.6% and 7.4% higher than the cases of the pristine ones, respectively. With the aid of Ti coatings, the interface bonding strength between cBN grits and Fe-based matrix was improved by 335 MPa in the Fe-based matrix/cBN composites.     

Investigation of fragments size resulting from dynamic fragmentation in melted state of laser shock-loaded tin

The understanding of dynamic fragmentation in shock-loaded metals and the evaluation of geometrical and kinematical properties of the resulting fragments are issues of considerable importance for both basic and applied science, for instance to predict the evolution of engineering structures submitted to high-velocity impact or explosive detonation. Among dynamic failure processes, spall fracture in solid materials has been extensively studied for many years, while scarce data can be found yet about how such phenomenon could evolve after partial or full melting on compression or on release. In this case, the dynamic fragmentation process, which may be referred to as ‘micro-spalling’, takes place in a liquid medium. It results in the formation of a cloud of fine molten droplets, ejected at high-velocity. The present work is devoted to experimental characterization, theoretical modelling and simulation of the ‘micro-spalling’ process in tin, with a specific emphasis on the size of the resulting fragments, namely the melted droplets. Laser-driven shock-loading experiments on tin have been performed. Post-test observations of the recovered fragments provide an insight into the actual fragmentation process and allow to infer the distribution of the fragments size which are found to be mostly sub-micrometric. Fragmentation modelling is based on a widely employed, energetic approach adapted to the case of liquids. This approach is implemented as a failure criterion in an one-dimensional hydrocode including a multiphase equation of state for tin. A fairly good agreement is obtained between experimental and computed sizes range. Some discrepancies are explained by both experimental uncertainties and model limitations which are carefully pointed out and discussed.