Radiative transfer model of a pyrotechnic flame

A two-line radiative transfer model for predicting the spectral radiant flux of pyrotechnic illuminating flares over a wide range of system variables such as formula, size, and ambient pressure, has been formulated and validated.To solve the transfer equation for observed radiant intensity, the flame is represented by a model whose main characteristics are (a) the flame is a homogeneous gaseous atmosphere with plane-parallel stratification, (b) the gas consists of inert molecules plus sodium atoms which can be excited to the ²P_{$\text{1}\text{2}$} or ²P_{$\text{3}\text{2}$} level, (c) there is local thermodynamic equilibrium governed by the local temperature, (d) the temperature gradient can be represented by a parabola whose vertex is at the center of the flame, (e) the dispersion profile and number density of sodium atoms have average values, inside the flame, that are independent of depth, and (f) the individual line dispersion profile is replaced with a two-line function to simultaneously describe the spectral distribution of both of the sodium D lines.The parameters of the radiative transfer theory were supplied from calculated thermodynamic properties of the flare. Optical thickness as a function of position in the flame was determined using computed sodium atom densities and physical flame size obtained photographically. A flame temperature gradient was constructed numerically as a function of temperature in the flame using the computed temperature at the flame center and the boundary. The two-line dispersion profile was constructed as a function of line broadening. The shape and intensity of the broadened flare spectrum was computed without introducing further assumptions.     

Absorption and emission line profile coefficients of multilevel atoms—II. Velocity-averaged profile coefficients

Starting from the atomic profile coefficients of a multilevel atom derived in the previous first part of this paper, we consider the velocity-averaged line profile coefficients appearing in the radiative transfer equation for the important special case that the velocity distribution of atoms in the ground state is Maxwellian and that the streaming of excited atoms is negligible. Elastic velocity-changing collisions of excited atoms with other particles are taken into account in the framework of a strong-collision model. Neglecting stimulated emissions, we obtain explicit, albeit in some cases approximate, expressions for the line profile coefficients of a three-level atom in terms of the specific radiation intensity locally present. The emission and absorption profile coefficients are written in a form that exhibits the various physical effects responsible for deviations of these profiles from complete redistribution. The case of two-level atoms in the presence of elastic collisions with the excited atoms is also treated.     

高激发态原子的相干效应

本文以高激发态原子为研究对象, 由基态、激发态和高激发态能级形成阶梯型三能级系统, 理论上求解阶梯型三能级系统的密度矩阵方程, 研究了高激发态原子的相干效应, 计算获得探测光的吸收和色散曲线. 并研究了高激发态原子间相互作用以及外加电场对相干效应的影响. 结果表明, 外加场可以使吸收和色散曲线产生频移.     

光子晶体光纤中调制不稳定现象与超连续光谱的产生

研究了光子晶体光纤中调制不稳定性效应.从非线性薛定谔方程出发，计算和分析了光子晶体光纤中反常色散区以及正常色散区内的调制不稳定性现象，详细讨论了超短脉冲的脉宽、峰值功率、高阶色散和高阶非线性效应（如脉冲内喇曼散射、自陡峭效应）对调制不稳定性产生的影响.结果表明：二阶色散对调制不稳定性的影响要远大于三阶色散，同时也发现随着初始脉冲宽度的减小，调制不稳定性旁瓣增大但是强度有所降低.另外还发现高阶非线效应如自陡峭和喇曼效应会在不同程度上抑制调制不稳定性.     

Influence of motion of radiating particles on the concentration distribution at the boundary of a flat,semi-infinite layer

The distribution of excited atoms near the surface limiting the half space has been determined. The transfer of the excited state by two mechanisms, absorption and reradiation of photons and space motion, has been taken into account. An analytical solution has been found for the integral equation describing joint diffusion of the photons and particles. The concentration of excited atoms at the half-space boundary, determined after accounting for their space motion, may differ by orders of magnitude from the values obtained by solving the Biberman-Holstein equation.     

Nonlinear polarization response of a gaseous medium in the regime of atom stabilization in a strong radiation field

The nonlinear polarization response of a quantum system modeling a silver atom in the field of high-intensity radiation in the IR and UV spectral ranges has been studied by direct numerical integration of a nonstationary Schrödinger equation. The domains of applicability of perturbation theory and polarization expansion in powers of the field intensity are determined. The contribution of excited atoms and electrons in a continuum to the atomic polarization response at the field frequency, which arises due to the radiation-induced excitation and photoionization processes, is analyzed. Features of the nonlinear response to an external field under conditions of atom stabilization are considered.     

Photonen-Korrelationen in der spontanen Emission eines Zwei-Atom-Systems

Photon-correlations in the Spontaneous Emission from a Two-atom System The intensity correlation function of the spontaneous radiation from an initially fully excited two-atom system is calculated using Lehmberg's master equation and the quantumfluctuation-regression theorem. Photon bunching and antibunching occur alternatively during the emission process. It depends on the direction of observation and on the distance between the two atoms which of these effects appears at first. Towards the end of the emission process strong enlarged coincidences can arise.     

Effect of a magnetic field on transit time of excited atoms in a dc arc plasma

Transit times of excited atoms in a dc arc plasma exposed to an inhomogeneous magnetic field are investigated at different values of the magnetic induction. At the optimal value, the transit time, electron pressure and spectral line intensities are maxima. The large increase of spectral line intensity is not proportional to the slight increase of transit time. The transit times of different atoms at the same value of the magnetic induction are approximately equal, whereas the spectral line intensities are different. The maximum transit time corresponds to minimum electron mobility. The arc-plasma temperature is directly proportional to the magnetic induction.     

200 nm-1000 nm spectra of light emitted in the impact of ~(40)Ar~(10+) upon Al and Si solid surfaces

This paper reports the measured results of the 200 nm-1000 nm characteristic spectral lines of Al, Si and Ar atoms when highly charged ions 40Ar10+ are incident upon Al and P-type Si surfaces. The ion 40Ar10+ is provided by the ECR ion source of the National Laboratory of the Heavy Ion Accelerator in Lanzhou. The results show that when the low-speed ions in the highly charged state interact with the solid surfaces, the characteristic spectral lines of the target atoms and ions spurted from the surfaces can be effectively excited. Moreover, because of the competition of the non-radiation de-excitation of the hollow atom by emitting secondary electrons with the de-excitation process by radiating photons, the spectral intensity of the characteristic spectral lines of Ar atoms on the P-type Si surface is, as a whole, greater than that of Ar atoms on the Al surface.     

Resolution enhancement in noise spectrum by using velocity selective optical pumping in cesium vapor

We demonstrate experimentally that the resolution of amplitude noise spectrum in Cs atomic vapor can be enhanced by narrowing the absorption using velocity selective optical pumping technique. It is found that the steep atomic dispersion accompanied by high absorption leads to more conversion of laser phase noise to amplitude noise, when the field propagates throughout the atoms, and meanwhile the spectral resolution is improved. The effect of optical pumping intensity on the spectrum resolution is experimentally discussed, and a theoretical explanation for this phenomenon is given, which shows that the phase-to-amplitude noise conversion is directly proportional to the dispersion of medium.     

Passive mode-locking upon limitation of the spectral width of a laser emission

An analysis is presented of passive locking of modes in lasers with an additional intracavity element that limits the spectral width of a laser emission due to frequency dispersion of an order higher than quadratic. It is found that spectral limitation of this type may give rise to a multiple-pulse regime of passive mode-locking. The laser mode of operation established after a transient process, in this case, appears to be multistable, with the number of pulses per axial period being dependent on the initial conditions of the lasing. It is shown that the dependence of the number of pulses on the pump power is of hysteretic character. The theoretical analysis and numerical simulation are carried out using an equation close to the Ginzburg-Landau equation. Specifically, the nonlinear losses and nonlinear refractive index are supposed to be inertia-less and proportional to the light intensity; the frequency dispersion of the gain and the refractive index are approximated by a quadratic dependence; and the frequency-dependent losses related to the additional spectral limitation of the laser emission are determined by fourth-order frequency dispersion. The possibility of using the characteristic features of mode-locking predicted for control of regimes of formation and propagation of ultrashort light pulses is discussed.     

碱金属原子多极极化率的解析计算及其应用

通过考虑碱金属原子中的价电子在模型势中的运动, 给出了碱金属原子激发态(包括分立谱和连续谱)的波函数, 导出了碱金属原子的多极动态极化率的计算式中所涉及的矩阵元的解析表达式, 实现了碱金属原子多极动态极化率的解析计算. 作为应用, 利用范德瓦尔斯相互作用系数与动态极化率之间的积分关系, 计算了异核基态碱金属原子间的三体相互作用系数, 将计算结果与此前用稳定变分方法得到的结果进行了比较, 结果显示两者是一致的. 此工作为后续研究激发态碱金属原子间的相互作用奠定了基础.     

Cobmecтhaя диффuзия фop;oh;ob и khcy;acтиц b пoлuБecкoheчhom пpocтpahcтbe—I pacпpeдeлehиe boзБuждehhьч aтomob b пoлuБecкoheчhom пpocтpahcтbe

The excited atom distribution produced by the simultaneous action process, namely, excitation transfer by radiation in a spectral line and spce movement of excited atoms, is considered. A kinetic equation describing these process is analysed. For steady-state conditions, an adympototic analytical solutio id obtained. This solution describes the concentration distribution of excited atoms for a plane geometry in a region which is a distance exceeding the effective free path away from the surface limiting the volume.The influence on the general solution of either the excitation transfer process id found as a function of the parameters involved.     

强激光场中长程势与短程势原子产生高次谐波与电离特性研究

用数值方法求解含时薛定谔方程，研究了具有长程势和短程势的一维原子在强激光场中的高次谐波和电离特性. 在强激光场中，长程势和短程势原子产生的高次谐波具有相似的特性，对应的平台和截止位置相同，但是短程势原子没有低阶的高次谐波，而长程势和短程势原子在激光场中的电离概率明显不同. 研究结果表明，原子的激发态结构对低阶的高次谐波和原子的电离概率有重要影响. 关键词： 强激光场 高次谐波 电离概率     

Spectroscopic diagnostics of the laser erosion plasma of an AgGaS<Subscript>2</Subscript> polycrystalline target

Results are presented from experimental studies of the radiation emitted from a plasma produced in vacuum after irradiating a polycrystalline target by 1.06-μm laser radiation with an intensity of (3–5)×10⁸ W/cm². Plasma radiation from regions located at distances of 1 and 7 mm from the target is analyzed. It is shown that the main contribution to the plasma radiation in the 220–600 nm spectral range is made by transitions from the excited states of single-charged Ag⁺ and S⁺ ions. The atomic component of plasma radiation is represented by intense spectral lines corresponding to transitions from the Rydberg states of Ag and Ga atoms, whereas no resonance lines of these atoms are observed.     

介质阻挡放电六边形斑图稳定过程的光谱研究

采用发射光谱法,首次研究了等离子体参数及激发状态对介质阻挡放电六边形斑图稳定性的影响。在氩气/空气混合气体的介质阻挡放电中,随着电压的升高,放电丝直径增大,六边形斑图逐渐稳定,同时放电颜色由紫色逐渐变为灰白色,说明其等离子体状态及参数可能发生了变化。测量了六边形斑图放电过程中氮分子谱线和氩原子谱线相对于氩原子763.51 nm的相对强度、分子振动温度和电子激发温度随外加电压的变化。结果发现：氮分子谱线相对强度随电压增加而降低,氩原子谱线相对强度却升高;分子振动温度与电子激发温度均随电压增加而增大。这些现象表明：随着电压增大,电子能量增加。由此,氩原子激发增多,放电丝直径增大,介质表面上沉积的壁电荷面积增大,放电丝之间的相互作用增强,六边形斑图趋于稳定。     

Essentially nonequilibrium steady state of atoms in an optical field

The kinetics of atoms in the monochromatic field of a standing wave has been considered taking into account the recoil effects that appear under the interaction of the atoms with photons of the field. It has been shown that the steady-state solution of the kinetic equation for the atomic density matrix can have considerable asymmetry in the phase space. There is also asymmetry in the fluxes of atoms in the ground and excited states, predominantly near the nodes of the optical field.     

Spectral dependence of polarization of cesium atoms during pumping by a narrowband semiconductor laser

It is found in an experiment with narrowband laser pumping of Cs atoms by light of the D ₂-line that the spectral dependence of the polarization of atoms significantly differs from the spectral dependence of the light absorption by nonpolarized atoms. The difference lies in a partial resolution of the hyperfine structure of the excited 6² P _3/2 state, which remains unresolved in the case of nonpolarized atoms. The shape of the spectral dependence of the atom polarization observed upon pumping with circularly polarized light differs from that in the case of the linear polarized pumping and depends strongly on the buffer gas pressure, which allows one to obtain experimental information on collisional relaxation in the excited state. Calculation for a cell with antirelaxation coating and a cell with helium (6-Torr pressure) gives spectral dependences that are qualitatively consistent with experiment.     

Dispersive characteristics of surface plasmon polaritons on negative refractive index gratings

The dispersive characteristics of surface plasmon polaritons (SPPs) supported by a periodically corrugated boundary between vacuum and a negative refractive index, isotropic material were studied theoretically by numerical solution of a dispersion equation. SPP dispersion curves were correlated with the optical response of the corrugated boundary in frequency regions where SPPs can be excited by a normally incident plane wave. Abrupt reflectivity variations, characterized by the presence of a near unity maximum and an almost zero minimum, were found in regions where the boundary without corrugation exhibits low reflectivity and rather featureless reflectivity curves.     

Dynamics of the collective spontaneous emission of two three-level atoms in a cavity

Based on the master equation for the density matrix, the collective spontaneous emission of two A-type three-level atoms interacting with two modes of a quantum electromagnetic field in a finite-Q cavity is studied. The evolution of the emission intensity for each mode is found for the case where both atoms are initially in the excited state.