Saha decrements and collisional-radiative recombination and ionization coefficients for a nonequilibrium oxygen plasma

Using a time-dependent approach, a collisional-radiative model is developed for an oxygen plasma. Effective recombination and ionization coefficients are calculated for two specific cases, optically thin and optically thick in bound-bound u.v. radiation. The steady-state population densities for neutral and ionic states are presented in terms of their deviations from Saha equilibrium predictions. These results show the approach of the plasma to a state of local thermodynamic equilibrium (LTE) as a function of electron temperature and density. The computations are for temperatures between 1.0 and 3.0 eV and electron densities between 10¹⁶ and 10¹⁹ cm^-3.     

An experimental investigation of partial LTE for lower excited levels of Ar(I) in a wall-confined,argon arc plasma

This paper contains experimental results on partial LTE in the lower excited levels of Ar(I). The experiments were performed in a well-confined argon arc source. The population densities were obtained from self-absorption measurements of the lines. Plasma parameters were determined spectroscopically; measurements included the electron density (from the H_β line width) and the electron temperature (from the Boltzmann plot for higher excited levels of Ar(I)). The results show that the levels 1s₅ to 1s₅ are in Saha-Boltzmann equilibrium for electron densities above 3 × 10¹⁶ cm^-3.     

Temporal changes of particle densities and temperatures in a decaying arc discharge

This study deals with a decaying argon plasma at atmospheric pressure. It is shown that cylindrical symmetry is maintained, which enables us to measure experimentally the plasma composition at any moment after the switch-off. The changes in the particle density and the kinetic temperature have been deduced. For an electron density lower than 3x10¹⁶cm^-3, equilibration of the electrons towards the gas temperature is observed. Partial LTE between electrons and excited atoms is discussed.     

Non-LTE diagnostic of an argon arc plasma

The plasma of an argon arc has been investigated by applying the partial LTE model (overpopulation of the ground state) and accounting for different kinetic temperatures of electrons and atoms. The plasma analysis is performed without making use of atomic constants (e.g. transition probabilities) from the literature. The experimental results show that LTE is obtained in the 4mm arc at atmospheric pressure for electron densities above 6×10¹⁶cm^-3. Below this value, increasing under-population of the excited levels with decreasing arc current can be observed. This deviation from LTE may explain some not understood results from previously published spectroscopic observations of argon plasmas.     

小尺寸瞬态等离子体电子密度光谱法试验研究

本文对SCB等离子体发射光谱进行了试验研究,在局部热力学平衡条件下,用AlⅠ394.40nm谱线Stark的展宽法测量了SCB等离子体的电子密度;在发射光谱和Saha方程理论的基础上,设计并建立一套测试仪器,时间分辨率为0.1μs,将其测量的电子密度与同种试验条件下的Stark展宽法得到的结果相比较,电子密度的数量级都为1015cm-3－1016cm-3,且随时间的变化的规律相同。     

Measurements of emission coefficient for continuum radiation from shock-heated krypton plasmas

Using a shock tube, the ξ factor of krypton has been determined at λ = 456.1 nm by observations of the continuum radiation and simultaneous interferometric measurements of the electron number density. For the electron-density range used (1×10¹⁶cm^-3?n_e?4×10¹⁶cm^-3), we obtain an increase in the ξ factor for decreasing electron densities. These results are compared with theoretical and other experimental data.     

Deep levels in gallium arsenide by capacitance methods

The three capacitance methods, i.e., TSCAP, PHCAP, and transient capacitance measurements, are applied to determine electronic properties of deep levels inn-GaAs. In the boat-grown wafer detected are the 0.30 eV electron trap withN _T =3.6×10¹⁶ cm^?3 andS _n =2.4×10^?15 cm², and the 0.75 eV electron trap withN _T =2.0×10¹⁶ cm^?3 andS _n =1.2×10^?14 cm². In the epitaxial wafer, the 0.45 eV hole trap is detected withN _T >1.5×10¹³ cm^?3 andS _p =1.4×10^?14 cm² as well as the 0.75 eV electron trap withN _T =2.4×10¹³ cm^?3.     

An investigation of the energy exchange mechanisms involving the 23S metastable level in an RF helium plasma

The energy exchange mechanisms present in a pure helium and a helium-neon plasma were investigated using spectroscopic diagnostic techniques. The plasma was spatially resolved and only the volume element at the plasma centerline was considered in the energy- exchange analysis. The experiment was conducted with a constant total pressure of 0·7 torr, a fixed oscillator frequency of 4 MHz, and a constant input power of 1·8 kW. Emission line spectroscopy was used to determine the population densities of 16 levels in the n³S, n³P, and n³D series. Spatially resolved, self-absorption measurements of the 2³P-2³S transition were used to determine the 2³S metastable level number density. The electron number density of 3·3 × 10¹³ cm^-3 was determined from the spatially resolved H_β blue wing profile, and a lower bound excitation temperature of 8800 °K was determined from a Boltzmann plot of the spatially resolved lower bound levels of the excited helium. The addition of 10% and 20% by volume of neon gas caused a measurable decrease in the population densities of the lower bound levels of helium, while the electron number density and lower bound excitation temperature remained unchanged. Three energy exchange models (local thermal equilibrium, corona, and collisional- radiative) were examined, and the collisional-radiative model was found to best describe the excitation processes for the 2³S level. This model was also appropriate for describing the helium-neon plasma at this level.     

Spectroscopic measurements in nitrogen arcs with respect to local thermodynamic equilibrium

A wall-stabilized nitrogen arc at atmospheric pressure was studied spectroscopically in the current range from 20 to 70 A with the aim of detecting departures from LTE. Measurements of the relative intensity of several N(I) lines showed that the populations of the upper excited states are in equilibrium for currents greater than approx. 25 A. Comparisons of the excitation temperatures obtained from relative intensities with the electron temperature and with the temperature curves calculated for different departures from LTE show that deviations from equilibrium are small at the arc center for electron densities above approx. 4 × 10¹⁶ cm^-3. Deviations between the radial profiles of the electron and excitation temperatures were observed for currents between 35 and 55 A.     

Many-body effects in the first excited subband of the n-inversion layer of Si

We have calculated the self-energies of electrons in the lowest and first excited sub-bands of Si inversion layers. The self-consistent wavefunctions calculated in the Hartree approximation were used, and dynamic screening was approximated by the Lundqvist-Overhauser model. The correlation energy of an electron in the excited band is quite large: about ?10 meV at an inversion layer density of 10¹¹ cm^?2 to about ?16 meV at 3 × 10¹² cm^?2. The calculated separation between subbands is in very good agreement with available experimental measurements. An exciton is predicted with a binding energy of 0.9 meV at N_inv = 10¹² cm^?2 calculated in the static approximation.     

Plasma production in a Cs vapor by a weak CW laser beam at 6010 Å

When a dye laser beam at 6010.5 Å (which excites the $\text{Cs 6}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→8D}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ transition), of power 0.1 W, is focused into a Cs vapor of density ? 10¹⁷ cm^-3, we observe a bright localized white glow near the laser focus. Our experiments indicate that this glow is due to the production of a Cs plasma, which exhibits many characteristics of a discharge plasma, like emission of numerous atomic lines and of recombination continua, plasma-broadening of atomic lines, and hysterisis. This laser-produced plasma is in Saha equilibrium with a typical electron density of 3 × 10¹⁴ cm^-3, and a typical electron temperature of 0.2 eV.     

激光加热充氖靶丸的压缩实验研究

在神光(10¹²W)激光器上,用充Ne靶丸开展了内爆压缩实验研究。结果表明:实现了激光加热靶丸的对称性内爆压缩,芯部电子密度达10²³cm^-3,平均内爆速度为3.3×10⁷cm/。 关键词：     

A laser interferometer for measuring electron densities in an arc plasma

A Michelson interferometer working simultaneously at two wavelengths is used to follow the decay of the electron density n_e along the axis of a short-circuited dc-argon arc. Using optical isolation, compensating mirrors and quadrature signal detection results in a random error of 1% for n_e=5×10¹⁶ cm^-3.     

Experimental transition probabilities for several spectral lines arising from the 5d 6s{8s, 7p, 5f, 5g} electronic configurations of Pb III

Transition probabilities for 30 spectral lines, arising from the 5d¹⁰ 6s{8s, 7p, 5f, 5g} electronic configurations of Pb III (20 measured for the first time), have been experimentally determined from measurements of emission line intensities in a plasma lead induced by ablation with a Nd:YAG laser. The line intensities were obtained with the target placed in molecular argon at 6 Torr, recorded at a 400 ns delay from the laser pulse, which provides appropriate measurement conditions, and analysed between 200 and 700 nm. They are measured when the plasma reaches local thermodynamic equilibrium (LTE). The plasma under study had an electron temperature (T) of 21,400 K and an electron number density (N_e) of 7×10¹⁶ cm⁻³. The influence of self-absorption has been estimated for every line, and plasma homogeneity has been checked. The values obtained were compared with previous experimental values and theoretical estimates where possible.     

Etude spectroscopique de l'effet d'anode

Spectral lines of LiI emitted by an anodic plasma, produced during electrolysis of a KCl-LiCl mixture, have been observed. This paper deals with diagnostic studies of this plasma and is based on a comparison of observed line profiles for LiI(2P-3D), (2P-4S) and (2P-4D, 4F) with calculated values derived from the Griem-Baranger impact theory. We have found, from the ensemble of the results, that the electron density in the plasma center is N_e(0) ? 1·8×10¹⁷ cm^-3, the electron temperature is T_e(0) ? 9×10³ °K, and the plasma thickness is l ? 200 μ.     

Spectroscopic diagnostics of carbon and aluminum laser-produced plasmas

VUV emission spectra of plasmas produced by focusing laser radiation with intensity of 10¹⁰–10¹¹ W/cm² on carbon and aluminum targets were studied. Using the partial local thermodynamic equilibrium model for an electron density exceeding 10¹⁷ cm^?3, the spectroscopic diagnostics and the analysis of ion composition of plasmas were carried out. The electron temperatures determined for carbon and aluminum plasmas from the ratio of intensities of ionic lines were found to be 8±3 eV and 11±4 eV, respectively. Stark broadening of aluminum lines was measured and parameters of electron broadening were determined. Using the spatially resolved measurement of Stark line broadening, the spatial density distribution and the law of electron gas expansion were found. The electron gas in the hot region of size 5 mm with an average density of (5±2) 10₁₇cm ^?3 experienced one-dimensional expansion according to the law 1/z ^1.1 with increasing distance z from the target.     

Effect of the pump absorption on generation of infrared stimulated electronic Raman scattering in alkali-metal vapors

The main properties of infrared stimulated electronic Raman scattering (SERS) at the 6² S _1/2-7² S _{1/2, 3/2} transitions in cesium atoms are studied theoretically and experimentally as functions of the atomic concentration, which was varied from 10¹¹ to 10¹⁶ cm^?3. It is found that the efficiency of generation of Stokes radiation strongly depends on one-photon absorption of the pump radiation tuned near frequencies of the 6² S _1/2-7² P _{1/2, 3/2} transitions. By using the equation for the density matrix, which describes the evolution of a three-level system, the theory of resonance excitation of IR radiation upon one-photon absorption at an adjacent transition is developed. The theory describes well the main features of IR SERS in alkali-metal vapors.     

Electrical conduction mechanism and carrier trapping in β-metal free phthalocyanine single crystals

The dark electrical conductivity of β-metal free phthalocyanine single crystals has been investigated over the temperature range 273–600°K, at a reduced pressure of 10^?7 torr. The results obtained are in accordance with the model proposed by Barbe and Westgate[5] for this material, in which the energy gap between the top of the valence band and the bottom of the conduction band is determined to be 2·00 eV. At temperatures below about 410°K, the conduction process is consistent with the presence of an electron trapping level located 0·32 eV below the conduction band edge, with a density of 7×10¹⁶ cm^?3, and a donor level of density 2×10⁷ cm^?3 at the same energy. Above about 410°K, there is evidence to suggest that the conduction process is intrinsic.     

1064 nm Nd:YAG激光诱导铁等离子体特征参数的研究

利用1064 nm Nd:YAG激光器研究了激光诱导铁条等离子体的特征参数。为了减小测量误差和谱线自发辐射跃迁几率不确定性带来的计算误差,采用改进的迭代Boltzmann方法精确求解铁等离子体的电子温度为8058 K。Lorentz函数拟合Fe I 376.553 nm得到等离子体的电子数密度为8.71017 cm-3。分析表明等离子体的加热机制主要是逆轫致过程,其吸收系数是0.14 cm-1。实验数据证实激光诱导铁等离子体处于局部热力学平衡状态和光学薄状态。     

激光产生蒸汽羽的干涉研究

 根据拍摄1.06 μm长脉冲钕玻璃激光与LY12铝靶耦合产生蒸汽羽的干涉分幅照片，测出在t<50 μs空气冲击波速度约为473 m/s而蒸汽羽阵面扩散速度约为162 m/s。运用蒸汽羽等离子体的有关热力学特性方程组，得到蒸汽羽等离子体的电子密度、电子温度、电离度和吸收系数的最大值分别为N_e≈3.1×10¹⁷ cm^-1，T≈6 096 K，η≈0.014，α_(1.06μm)≈0.03 cm^-1的结果。