Spatial and temporal evolution of argon sparks

Optical emission spectroscopic studies of laser-created argon sparks are carried out. Pulses of 532 nm and 8 ns from a frequency-doubled Nd:YAG laser are used to create an argon spark at 1 atm. Gated photography of 2 ns is used to investigate spark evolution at early times. Electron temperature and density measurements are made from the spectral data. The Stark broadening of emission lines is used to determine the electron density, and the Boltzmann plot of the singly ionized argon-line intensities is exploited for determination of the electron temperature. The dependence on electron temperature and density on different experimental parameters, such as distance from the focal point, delay time after the initiation of the spark, and laser energy, are discussed.     

Energy absorption and propagation in laser-created sparks

The energy absorption and laser propagation characteristics of air and argon sparks at one atmosphere have been investigated. To create the sparks, 532 nm pulses from a frequency doubled Q-switched Nd : YAG laser are used. We employed 2 ns gated fast photography for studying the time evolution of the kernel at early times. Optical emission spectroscopy is used to infer temperature and density of the sparks. Significant energy absorption by the plasma is observed just above the breakdown threshold. The energy absorption and propagation in the spark indicated that argon plasma is more absorptive than air plasma. The absorption of the spark increases with laser energy, and at higher energies absorption saturation is observed. A spiky behavior is observed in the transmitted temporal profiles of lasers at higher energies and this is explained as due to the formation of a self-regulating regime.     

Optical emission from laser-induced breakdown plasma of solid and liquid samples in the presence of a magnetic field

The optical properties of laser-induced plasma generated firm solid (Al alloy) and liquid (Mn, Cr, Mg, or Ti solutions) samples expanded across an external, steady magnetic field have been studied by atomic-emission spectroscopy. Various line emissions obtained from the constituents of the Al alloy and of the aqueous solution show an enhancement in intensity in the presence of an approximately 5-kG magnetic field. The enhancement of the signal was nearly a factor of 2 for the minor constituents of the solid samples and a factor of 1.5 for the elements in liquid phase. Temporal evolution of the emission from the solid sample showed maximum enhancement in emission intensity at 3-10-micros time delay after plasma formation in the laser energy range 10-50 mJ. However, for the liquid sample the maximum signal was for a gate delay of 3-25 micros the energy range 50-200 mJ. This enhancement in the emission intensity was found to be due to an increase in effective density of the plasma as a result of magnetic confinement when the plasma cooled after expansion. This enhanced emission was due to an increase in the rate of radiative recombination in the plasma.     

Determination of the maximum temperature at the center of an optically thick laser-induced plasma using self-reversed spectral lines

A method of temperature measurement based on the model developed by Bartels of an optically thick inhomogeneous plasma was applied to a laser plasma induced on a target containing barium. The method involves the intensity ratio measurement of two self-reversed Ba(II) lines. The temperature thus determined corresponds to the maximum temperature in the plasma center. The plasma temperature was measured for delay times between 0.5 micros and 10 micros in two spectrometer operating modes: the scanning mode and the dual-wavelength mode, the latter resulting in better precision. A detailed analysis of experimental errors was performed. The error strongly depended on the wavelength separation of the lines used. The most accurate results were obtained for the largest line separation. Using one line in the UV and the other in the visible region, the relative error was 2-6% for temperatures between 8000 K and 20 000 K. The distribution of the plasma temperature along the plasma height was measured in the same delay time range. The temperature was found to be uniform along the plasma vertical axis, thus confirming the plasma cylindrical symmetry.     

Ultrafast microfluidic mixer and freeze-quenching device

The freeze-quenching technique is extremely useful for trapping meta-stable intermediates populated during fast chemical or biochemical reactions. The application of this technique, however, is limited by the long mixing time of conventional solution mixers and the slow freezing time of cryogenic fluids. To overcome these problems, we have designed and tested a novel microfluidic silicon mixer equipped with a new freeze-quenching device, with which reactions can be followed down to 50 micros. In the microfluidic silicon mixer, seven 10-microm-diameter vertical pillars are arranged perpendicular to the flow direction and in a staggered fashion in the 450-pL mixing chamber to enhance turbulent mixing. The mixed-solution jet, with a cross section of 10 microm x 100 microm, exits from the microfluidic silicon mixer with a linear flow velocity of 20 m/s. It instantaneously freezes on one of two rotating copper wheels maintained at 77 K and is subsequently ground into an ultrafine powder. The ultrafine frozen powder exhibits excellent spectral quality and high packing factor and can be readily transferred between spectroscopic observation cells. The microfluidic mixer was tested by the reaction between azide and myoglobin at pH 5.0. It was found that complete mixing was achieved within the mixing dead time of the mixer (20 micros), and the first observable point for this coupled device was determined to be 50 micros, which is approximately 2 orders of magnitude faster than commercially available instruments.     

光谱分析钢中氮元素波动因素的探讨和改进

本文利用ARL4460型火花源光电直读光谱仪,通过对样面质量、分析条件、工作曲线、仪器波动、人为因素等方面的分析以及精密度和比对试验,找出引起火花源原子发射光谱法测定钢中氮元素波动的主要因素为样品纹路不清晰,氩气纯度不够,氩气流量调节不合适,火花台脏气路堵塞,采取相应措施,取得满意效果。     

Study of laser-induced breakdown emission from liquid under double-pulse excitation

The application of laser-induced breakdown spectroscopy to liquid samples, by use of a Nd:YAG laser in double-pulse excitation mode, is described. It is found that the line emission from a magnesium ion or atom is more than six times greater for double-pulse excitation than for single-pulse excitation. The effect of interpulse separation on the emission intensity of a magnesium ion and a neutral atom showed an optimum enhancement at a delay of 2.5-3 micros. The intensity of neutral atomic line emission dominates the ion emission from the plasma for higher interpulse (>10 micros) separation. A study of the temporal evolution of the line emission from the plasma shows that the background as well as line emission decays faster in double-pulse excitation than in single-pulse excitation. The enhancement in the emission seems to be dominated by an increase in the volume of the emitting gas. The limit of detection for a magnesium solution improved from 230 parts per billion (ppb) in single-pulse mode to 69 ppb in double-pulse mode.     

Investigation of ignition of hydrogen–oxygen mixtures within the range of temperatures from 700 to 2500 K

The results of numerical modeling of the ignition process of hydrogen–oxygen mixtures diluted with argon at temperatures of 700–2500 K within wide ranges of the initial gas parameters are presented. The time evolutions of the concentration of the electron-excited radical OH* and other components, as well as the strength of the radical total radiation on wavelengths about λ = 306.4 nm, are calculated. Their peculiarities are described and the correspondence between the measured radiation strength scans obtained in the experiments by the emission method and those calculated in the process of modeling is determined. The temperatures upon which the mixtures ignite are determined. The dependences of the time delay of the ignition of the mixture on the pressure and component composition are found. The relationships are used to obtain the temperature dependence of the ignition time delay reduced to a preliminarily chosen pressure and gas composition.     

Spatial characterization of laser-induced plasmas by deconvolution of spatially resolved spectra

The spatial characterization of laser-induced plasmas, including their temperature, electron density, and relative atom density, has been carried out by emission spectroscopy. The plasmas were generated with iron samples in air and argon at atmospheric pressure. An imaging spectrometer equipped with an intensified CCD detector procured spectra with spatial resolution. The plasma characterization was made at three temporal gates (2-3, 5-6, and 9-11 micros) to permit the plasma's evolution to be studied. A deconvolution procedure was developed to transform the measured intensity, integrated along the line of sight, into the radial distribution of emissivity. Temperature and electron density distributions were obtained under the assumption of local thermodynamic equilibrium and Stark broadening of the emission lines. The relative atom density distributions in the plasma of the Fe atoms arising from the sample and of the Ar atoms arising from the ambient gas were determined and evidenced an important interaction between the plasma and the surrounding atmosphere.     

Thermoluminescence of PbWO4 irradiated with UV light

PbWO4 single crystals were grown by the Czochralski method in argon and air. The glow curves induced by UV light and the absorption spectra of PbWO4 annealed at various temperatures were measured. The glow curves of PbWO4 were strongly dependent on the growing atmospheres. The activation energies of the 110 K peak of PbWO4 grown in argon and the 122 K peak of PbWO4 grown in air were calculated to be 0.23 eV and 0.29 eV, respectively. The ratio of the 2.76 eV emission band to the 2.48 eV or 2.26 eV emission bands of the PbWO4 grown in air was smaller than that of the PbWO4 grown in argon. The glow curve of PbWO4 grown in argon was similar to that of PbWO4 grown in air when the annealing temperatures were increased.     

On the origin of gamma-ray bursts

Gamma-ray bursts are the most energetic explosions in the Universe, occurring at cosmological distances. The initial phase of the emission from these bursts is predominantly of gamma rays and stems from a highly relativistic outflow. The nature of this emission is still under debate. Here, I present the interpretation that the peak in the photon spectrum can be attributed to the black-body emission of the photosphere of the outflow, having a temperature of approximately 109K. An additional non-thermal spectral component can be attributed to additional dissipation of the kinetic energy in the outflow. This two-component model can be well fitted to most instantaneous spectra. Interestingly, the thermal component exhibits a recurring behaviour over emission pulse structures. Both the temperature and the energy flux vary as broken power laws. During the pre-break phase, the temperature is approximately constant while the energy flux rises. Furthermore, the ratio of the observed thermal flux to the emergent flux increases as a power law over the whole pulse. It is argued that these observations hold the key to our understanding of the prompt emission and the properties of the site from which it emanates.     

The Design of Dual Work Function CMOS Transistors and Circuits Using Silicon Nanowire Technology

This exploratory study on vertical, undoped silicon nanowire transistors shows less power dissipation with respect to the bulk and SOI MOS transistors while yielding comparable performance. The design cycle starts with determining individual metal gate work functions for each nMOS and pMOS transistor as a function of wire radius to produce a 300 mV threshold voltage. Wire radius and effective channel length are both varied until a common body geometry is determined for both nMOS and pMOS transistors to limit off currents under 1 pA while producing highest on currents. DC characteristics of the optimum n and p-channel transistors such as threshold voltage roll-off, DIBL and subthreshold slope are measured; simple CMOS gates including an inverter, 2- and 3-input nand, nor, and xor gates, and full adder are built to measure the transient performance, power dissipation and layout area. Postlayout simulation results indicate that the worst case delay for a full adder circuit is 8.5 ps at no load and increases by 0.15 ps/aF; worst case power dissipation of the same circuit is 23.6 nW at no load and increases by 4.04 nW/aF at 1 GHz. The full adder layout area occupies approximately 0.11 mum²     

Measurement and analysis of OH emission spectra following laser-induced optical breakdown in air

The measured emission spectra of the OH radical subsequent to laser-induced optical breakdown in air are analyzed to infer spectroscopic temperature and species number density. Emissions from the UV A2sigma+ --> X2IIi transition dominate the spectra in the wavelength range of 306-322 nm and for time delays from the optical breakdown of 30-300 micros. Contributions from other species to the recorded OH emission spectra were also investigated for spectroscopic temperature measurements in the range of 2000-6000 K and for OH number densities in the range of 10(14) - 2 x 10(16) cm(-3). Monte Carlo simulations are applied to estimate errors in the analysis of the hydroxyl spectra.     

Mechanisms of pulsed laser microbeam release of SU-8 polymer "micropallets" for the collection and separation of adherent cells

The release of individual polymer micropallets from glass substrates using highly focused laser pulses has been demonstrated for the efficient separation, collection, and expansion of single, adherent cells from a heterogeneous cell population. Here, we use fast-frame photography to examine the mechanism and dynamics of micropallet release produced by pulsed laser microbeam irradiation at lambda = 532 nm using pulse durations ranging between 240 ps and 6 ns. The time-resolved images show the laser microbeam irradiation to result in plasma formation at the interface between the glass coverslip and the polymer micropallet. The plasma formation results in the emission of a shock wave and the ablation of material within the focal volume. Ablation products are generated at high pressure due to the confinement offered by the polymer adhesion to the glass substrate. The ablation products expand underneath the micropallet on a time scale of several hundred nanoseconds. This expansion disrupts the polymer-glass interface and accomplishes the release of the pallet from its glass substrate on the microsecond time scale (approximately 1.5 micros). Our experimental investigation demonstrates that the threshold energy for pallet release is constant (approximately 2 microJ) over a 25-fold range of pulse duration spanning the picosecond to nanosecond domain. Taken together, these results implicate that pallet release accomplished via pulsed laser microbeam irradiation is an energy-driven plasma-mediated ablation process.     

Capabilities of surface composition analysis using a long laser-induced breakdown spectroscopy spark

An apparatus has been investigated based on laser-induced breakdown spectroscopy (LIBS) for the rapid determination of the spatial distribution of elements on surfaces. Cylindrical optics are used to create a linear spark approximately 1 cm in length. Light emitted by atoms excited along the spark is collected and provides a spatial profile of elemental composition in the sample when analyzed with a spectrometer and gated charge-coupled device (ICCD) detector. Moving the spark across the sample surface as spectral data is recorded at regularly spaced intervals allows for the development of a three-dimensional elemental distribution map (emission intensity versus spatial distribution across an area). An analysis of the spatial resolution of this methodology is presented along with representative data from several sample types. Application of full-image analysis allowing for simultaneous investigations into the spatial distributions of multiple elements is also discussed and results are presented.     

Optical and electrical properties of ZnO nanoparticle thin films deposited on quartz by sparking process

ZnO nanoparticle thin films were deposited on quartz substrates by a novel sparking deposition which is a simple and cost-effective technique. The sparking off two zinc tips above the substrate was done repeatedly 50-200 times through a high voltage of 10 kV in air at atmospheric pressure. The film deposition rate by sparking process was approximately 1.0 nm/spark. The ZnO thin films were characterized by X-ray diffraction, Raman spectroscopy, UV-vis spectrophotometry, and ionoluminescence at room temperature. The two broad emission peaks centered at 483 nm (green emission) and 650 nm (orange-red emission) were varied after two-step annealing treatments at 400-800 °C. Moreover, the electrical resistivity of the films was likely to be proportional to the peak intensity of the orange-red emission.     

Spectroscopic study of an electrode microwave discharge in argon and argon-hydrogen mixtures

The results of an optical emission spectroscopy study of low-pressure microwave induced discharge in argon, argon-hydrogen (0.9% H₂) and hydrogen-argon (5% Ar) mixture are reported. At four different pressures the Boltzman plot of relative ArI line intensities is used to measure electron excitation temperature, which was close to 3000 K in argon and in argon-hydrogen mixture discharges. The spatial distributions of light emission from argon and hydrogen-argon discharges are recorded with CCD camera and compared with spectroscopically observed spatial distributions of the ArI 415.8 nm line intensity in argon and the H_β line intensity in hydrogen-argon mixture at three different pressures. The variation of light intensity with pressure for argon lines ArI 842.5 nm, ArI 750.3 nm and ArI 419.8 nm as well as for hydrogen H_β line is also studied. For high- and low-lying energy levels in argon and in argon-hydrogen mixture, a different dependence of spectral line intensity upon gas pressure is detected. In hydrogen-argon mixture, a non-linear decrease of argon and hydrogen spectral line intensity with an increase of gas pressure is observed.     

Spatially resolved, laser-induced breakdown spectroscopy, development, and application for the analysis of Al and Si in nickel-based alloys

Spatially resolved laser-induced breakdown spectroscopy (SRLIBS) was used for the characterization of aluminum and silicon in nickel-based alloys. The very low invasiveness of the technique was one of the figures of merit of LIBS; however, the relative complexity of the instrument often hindered the widely acceptance of LIBS. Spatially resolved LIBS could provide accuracy and precision comparable to those obtained with temporally resolved LIBS (TRLIBS). In the nongated spatially resolved LIBS, the maximum atomic emission could be obtained with relative low continuum background emission at optimum observation spatial position. The study was done with a Nd:YAG laser at 532 nm, 3.0 mJ laser energy, and 0.2 mbar in argon. The experimental results obtained under optimum conditions were compared to those obtained with TRLIBS. SRLIBS gave reliable results without the tedious optimization of the delay time and gate width.     

A test of a planar spark counter of 500 μm spark gap

A planar spark counter of 500 μm spark gap was tested with cosmic rays. A time resolution of 134 ps was achieved. The test was carried out for several quenching gas pressures. The best performance was obtained at a gas pressure of 4 atm (2.5 atm of argon and 1.5 atm of the quenching gas). The counter efficiency was about 93%. This low pressure permits easy construction of the counter with a thin pressure vessel. Subsequent measurements using ⁶⁰Co γ-ray sources gave a discharged area of about 5 mm in diameter.     

用火花塞光纤传感器测量发动机的爆震

应用所研制的火花塞光纤传感测量系统对ＢＪ４９２Ｑ汽油机进行爆震燃烧测量和研究。分析了爆震燃烧对火焰光辐射变化的影响。正常燃烧理论空燃比工况时，ＣＨ（４３１．５ｎｍ），Ｃ２（５１６．５ｎｍ）及Ｈ２Ｏ（５８８ｎｍ）自由基的光强曲线出现双峰值，着火延迟期内光辐射为自由基的光辐射。爆震燃烧较强工况，只出现一个较大光强峰值，主要是碳粒子的热辐射，峰值处出现剧烈波动，相位提前，无自由基光辐射。爆震燃烧较强峰值