A scheme of chemical plasma laser

In case of intense recombination in a dense plasma of complex chemical composition, high rate chemical reaction can clean out the ground states of atoms and slightly affect on the population of excited states. A scheme of amplification the resonance emission of atom Tl is proposed.     

A recombination laser from cooled hydrogen plasma (plasma dynamic laser)

Using our time-dependent model we calculate the inversion density and gain for a visible line (6563 Å) from hydrogen as a result of rapid cooling of a plasma. A visible plasma dynamic laser is shown to be possible under certain conditions.     

准分子激光诱导铅等离子体中谱线Stark展宽时空特性研究

测定了激光诱导铅等离子体中铅原子和离子谱线Ｓｔａｒｋ展宽的时间演化特性以及与缓冲气体压力之间的关系,由此计算得到了等离子体中电子密度的时间演化特性及其与缓冲气体压力之间的关系,实验结果表明,由不同的金属固体材料产生的激光等离子体的动力学性质差异很大,并讨论了形成这种差异的物理机制。     

A steady-state fluid model of the coaxial plasma gun

The plasma layer in a coaxial plasma gun is considered as a shock front driven by expanding magnetic fields. Analytical steady-state solutions of the fluid equations yield the plasma properties, allowing the scaling of plasma focus devices.     

Ionization effect to plasma expansion study during nanosecond pulsed laser deposition

The dynamic characteristic and effects of plasma play an important role in film growth process of pulsed laser deposition (PLD). Based on numerical hydrodynamic modeling, supposed the laser radiation and partial ionization of the plasma as a dynamic source, we deduce a set of new plasma expansion dynamics equations. Based on which, as an example of carbon target, using finite difference method, the plasma flow dynamics evolvement in vacuum is investigated. Our results show the dynamic partial ionization increases the expansion in all directions, which changes into a new dynamic source for plasma expansion. In the axial direction, because of the collisional interactions between particles, the plume density peak is in the vicinity of the target surface and the acceleration of plasma occurs mainly near the target surface too. In the transverse direction, the plume peak is not near the target, but at the surface. The space expansion distance is far less than the axial direction because there is no high initial velocity component in this direction. The predictions of the plasma expansion action based on the proposed dynamics source assumption are found to be in agreement with the experimental observation.     

A study of balancing the competing effects of ultrashort laser induced plasma for optimal laser machining

We report that plasma generated during processing of materials with ultrashort pulse lasers and the associated high intensity optical beam have both favourable and unfavourable impact on the machined surface quality. Intensity of the optical beam propagating through ambient air medium enhanced further by self-focusing is sufficiently high to cause gas breakdown forming air plasma. The generated plasma reduces the effect of self-focusing but also distorts the beam profile. Duration of the pulse being too short for thermal equilibrium to establish, ablation occurs largely by direct removal of the material forming another plasma plume. Normally, the scattering effect of plasma results in distortions of the fabricated features. However, for certain parameter ranges, the competing self-focusing and gas plasma plumes supplemented with the material plasma can combine to cause filamentation, eliminating the distortions. Filament of hot plasma also acts as a well-shaped energy source. In the present study, brass is taken as an example for the investigation. Experiments were conducted to capture the spectrum of the light scattered by plasma using a spectrometer. Analysis was done to estimate the material plasma. Theoretical calculation on the intensity distribution in an optical beam propagating through air was then followed for a range of parameter values taking the self-focusing effect of the medium and the impact of the plasma generated by its breakdown. Approximate values of the machining parameters for clean fabrication are deduced from the calculations, which were used to conduct a laser machining test on brass.     

Regimes of laser plasma expansion at optical breakdown in the normal atmosphere

Propagation regimes of a plasma (fast ionization wave, laser-supported radiation wave, and laser-supported detonation wave) generated by laser radiation in a wide range of intensities (5 × 10⁸?10¹¹ W/cm² ) are described. The regimes were analyzed on the basis of the calculated dependence of the propagation velocity on the laser radiation intensity. The lower bound of the velocity was used for the fast ionization wave. Calculation results agree with experimental data and show that the plasma propagates as a fast ionization wave in the above range of intensities.     

Computational model of laser induced “hole burning” in a dense carbon plasma

A high density laser produced carbon plasma is heated with the beam from a pulsed CO₂ laser. The resulting density depression is modelled by a 2D computer code.     

A cadmium photoionization laser pumped by laser induced plasma radiation from a multi foci device

Soft x-rays from a laser-produced plasma were used to perform innershell photoionization of Cd atoms and to generate laser radiation at 442 nm. To achieve longer interaction zones between the Cd vapor and the soft x-ray flux, up to three plasma spots have been applied. In this way a maximum laser energy of 300 J with a 600 mJ Nd:YAG laser for the plasma production was achieved. Experimental investigations and corresponding rate-equation calculations indicate, that photoelectrons play an important role in the total laser kinetics.     

A two-dimensional multispecies fluid model of the plasma in an ACplasma display panel

A time dependent, two-dimensional model for simulating the plasma evolution in an AC plasma display panel (AC-PDP) is described. Reaction-convection (mobility)-diffusion equations for charged particles and excited heavy neutral species are solved along with Poisson's equation, a radiation transport equation, a surface charge buildup equation, and an external L-R-C circuit equation using a fully implicit numerical method. Electron-driven rate coefficients are computed with a 0-D Boltzmann solver in the local field approximation. For studying the particle dynamics in pure helium, we consider a reduced model in which radiation transport is ignored and the excited species manifold is collapsed to composite metastable and excited states. The model predictions of breakdown voltage are quite sensitive to the value of the secondary electron emission coefficient assumed and the uncertainties in the electron-driven reaction rates. An initial comparison between the model predictions and I-V measurements from a specially constructed helium-filled panel is made with qualitatively similar behavior. The lack of quantitative agreement can be explained by a combination of uncertainties in the model input data and uncertainty in the initial surface charge state in the experiments     

激光等离子体光丝中太赫兹频谱的调控

研究了双色激光场激发空气成丝产生太赫兹辐射频谱的变化规律.实验观察到随驱动光功率和光丝长度增加,太赫兹光谱主要发生红移的现象.分析表明,由于等离子体密度的增加,太赫兹辐射的趋肤深度减小,等离子体吸收主导了红移的发生.在光丝足够短的条件下,趋肤深度远大于光丝长度,从而产生等离子体振荡主导的太赫兹辐射光谱蓝移.本研究为超快宽带太赫兹辐射的频谱调控提供了新思路.     

化学反应与饱和模型对化学氧碘激光性能的影响

 将速率方程（RE）模型与化学动力学模型相结合，讨论了增益饱和模型与化学反应系统对COIL性能的影响。流动为预混的一维模型，考虑了10种成分和21个化学反应，分析计算了未分解碘分子，激发态氧产率，水含量以及温度等因素对COIL性能的影响。计算结果表明，碘流量过多，混合和反应过程中消耗大量能量；碘流量过低，导致粒子数反转和增益过低，对于能量的提取不利。     

Subpicosecond laser ablation of copper and fused silica: Initiation threshold and plasma expansion

We investigated the subpicosecond laser ablation of copper and fused silica under 100 fs laser irradiation at 800 nm in vacuum by means of fast plume imaging and time- and space-resolved optical emission spectroscopy. We found that, to the difference of copper ablation, the laser-generated plasma from a fused silica target exhibited one “main” component only. The “slow” plasma component, observed during copper ablation and usually assigned to optical emission from nanoparticles was not detected by either plasma fast imaging or optical emission spectroscopy even when fused silica targets were submitted to the highest incident fluences used in our experiments. The characteristic expansion velocity of this unique component was about three times larger than the velocity of the fast plume component observed during copper ablation. The dependence of laser fluence on both plasma expansion and ablation rate was investigated and discussed in terms of ablation efficiency and initiation mechanisms.     

High-power 20-channel neodymium glass laser and combined laser and beam heating of a plasma

A high-power 20-channel neodymium-glass laser is described (energy i kJ, pulse duration 2 nsec). It is part of the Flora facility intended for combined simultaneous heating of a plasma by powerful laser radiation (PLR) and by a relativistic electron beam (REB) produced in a facility of the plasma focus type. The paper deals theoretically with the processes of combined interaction of PLR and REB with a current plasma and a solid target.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 103, pp. 202–230, 1978.     

Applicability of the ideal fluid model in high-temperature plasma physics

The dependence of the momentum flux density on the particle flux and pressure tensor is calculated for a relativistic collisionless plasma. It is shown that the relativistic plasma is not representable by the ideal fluid model in the presence of longitudinal and transverse perturbations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 80–83, April, 1989.     

Gas dynamic model of the expansion of a supercritical carbon dioxide pulse jet: A self-similar solution

The unsteady-state isentropic expansion of an initially homogeneous spherical cloud of a van der Waals gas into a vacuum is considered as a dynamic part of the problem of modeling a real gas pulse jet. A self-similar solution of the gas dynamic equations is obtained. The parameters of the pulse jet (density and temperature) that simulate the conditions of a real experiment are calculated.     

激光诱导等离子体的气体动力学和燃烧波扩展速度研究

针对激光对熔石英材料产生致燃损伤过程中存在的激光支持燃烧波,考虑激光作用的温度残余、目标形貌的改变、喷溅物质分布、目标表面气流状况的分布等效应,分阶段对激光支持燃烧波的过程进行建模和仿真研究.通过建立二维轴对称气体动力学模型,模拟研究包含逆韧致辐射、热辐射、热传导和对流过程在内的激光能量传输过程.此外,依据激光支持燃烧波在可见光波段具有明显的辐射特征这一特点,利用阴影法测量了激光对熔石英致燃损伤过程中的燃烧波扩展速度,得到了燃烧波演化过程图像.研究结果表明:在平行激光束作用下,燃烧波的传播是稳态的,气体动力学行为比较稳定;在聚焦激光束作用下,燃烧波的传播是非稳态的.模拟结果中得到的激光支持燃烧波扩展速度及气体动力学结构与实验结果和理论推导结果符合得很好,验证了理论模型的正确性.