Evaluation of downstream-mixing scheme for 9.4-µm CO2 gasdynamic laser

A theoretical analysis of a downstream-mixing 16-μm CO₂ gasdynamic laser revealed the possibility of utilizing the downstream-mixing scheme for the generation of 9.4-μm radiation using a CO₂ gasdynamic laser. The flow-field has been analyzed using complete two-dimensional, unsteady laminar form of Navier-Stokes equations coupled with the finite rate vibrational kinetic equations. The analysis showed that integrated small-signal gain of 11.5m⁻¹ for Lorentzian broadening and 4.8m⁻¹ considering Voigt function can be obtained for N₂ reservoir temperature of 2000°K and velocity ratio 1:1 between the CO₂ and N₂ mixing streams. These results (presented in graphs) clearly highlight the large potential of downstream-mixing CO₂ gasdynamic laser for 9.4-μm laser generation.     

Pulsating optical source appearing under continuous laser energy supply to a hypersonic air flow

The spatio-temporal gasdynamic structures of plasma formations produced in a hypersonic air flow by a focused high-power laser beam are analyzed numerically using the model of inviscid non-heat-conducting equilibrium radiating air. The reasons for the emergence of pulsating gasdynamic nonuniformity in the region between the bow shock wave and the intense laser radiation absorption zone are investigated.     

气动激光器喷管非平衡流2维数值仿真

将Anderson的两振型三温度弛豫模型和严海星整理的弛豫数据相结合,采用2维守恒型方程组对按照最小长度喷管型面设计方法设计的、面积比分别为50和20的气动激光器喷管非平衡流场进行了数值仿真。小信号增益计算结果在每个计算点都和J.S.Vamos等人针对这两种喷管的小信号增益测量试验结果符合很好.解决了传统的准1维非平衡流分析方法不能很好地和试验结果相符的问题.对气动激光器喷管性能设计提供了更精确的评估方法。     

Gas dynamics in nuclear-pumped laser and luminescent cells with buffer volumes

A nonstationary gasdynamic model of sealed laser and luminescent cells pumped by uranium fission fragments is developed. This model extends the earlier 1D model of gas dynamics in cells of flat geometry to the case of cells with buffer volumes and allows analysis of gasdynamic processes for the energy deposition step distribution over the laser cell length.     

Gasdynamic CS2 laser with an aim of increasing the efficiency and expanding the spectral range of lasers of this type

The gasdynamic CS₂ laser is investigated theoretically and experimentally. It is theoretically demonstrated that the efficiency of the gasdynamic lasers can be increased by using molecules with lower-lying laser and pumping levels than in the case of C0₂ or N₂0 gasdynamic layers. Calculations show that under gasdynamic laser conditions, inversion should set in for an entire series of CS₂ molecular transitions in the range 11.4–117 m. Lasing with wavelength 11.4 m was obtained in experiment on the (00⁰1)-(10⁰0) transition.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 113, pp. 168–183, 1979.     

The effect of the polytropic index γ on the structure of gaseous detonations

The present study aims to clarify the effect of the polytropic index (i.e., the ratio of specific heats in the context of a perfect gas) on the detonation structure. This is addressed by two-dimensional numerical simulations. To ease the clarification of the role of gasdynamics, a simple Arrhenius kinetic law is used for the chemical model. The activation energy, normalized by the shock temperature, is kept constant to obtain the same reaction rate sensitivity to temperature in all considered mixtures. This procedure dissociates the gasdynamic effects from the chemistry effects. The numerical results reveal that in mixtures with low polytropic indicies, the convective mixing is enhanced compared to mixtures with higher polytropic indicies. The mixing is evaluated using Lagrangian tracers. Moreover, mixtures with low polytropic indicies are found to have a shorter reaction length than mixtures with high polytropic indicies. Also, for the range of parameters considered in this study the results indicate that Mach stem bifurcation in detonations due to jetting is primarily a gasdynamic driven mechanism.     

Self-similar solutions of laser produced blast waves

The aerodynamics of the blast wave produced by laser ablation is studied using the piston analogy. The unsteady one-dimensional gasdynamic equations governing the flow are solved under assumption of self-similarity. The solutions are utilized to obtain analytical expressions for the velocity, density, pressure and temperature distributions. The results predict all the experimentally observed features of the laser produced blast waves.     

Computer simulation of expansion of a carbon laser plasma after ablation in nitrogen atmosphere

Computer simulation is employed for analyzing the dynamics of plasma expansion in nitrogen under a pressure of 103 and 104 Pa after the action of a nanosecond laser pulse on a graphite plate for obtaining carbonitride nanofilms with the help of laser ablation technology. The binary gas mixture is described using a macroscopic quasi-gasdynamic model taking into account momentum and energy transfer between mixture components. The results of simulation are compared for various initial values of temperature and pressure of the laser jet with the results of direct Monte Carlo simulation and with experimental data. The possibility of controlling the shock wave propagation modes after ablation by varying the initial values of gasdynamic parameters is demonstrated. The effect of nitrogen atmosphere on the propagation of the laser jet is studied.     

An optimization analysis on the molecular vibrational energy eigenvalues of a diatomic gasdynamic laser

We study briefly the eigenvalue spectrum corresponding to the vibrational-energy levels of the molecules as anharmonic oscillators in a diatomic gasdynamic laser by calculating the maximum eigenvalue when all the possible diatomic configurations are considered within the context of gasdynamic lasers. In this context, a parameter which characterizes the anharmonicity of a given diatomic molecule as a one-dimensional oscillator is used in our calculations.     

Numerical simulation and experimental research on the effect of syneresis on the propagation of shock waves in a gas-liquid foam

A modified Godunov scheme possessing monotonicity and second-order accuracy is used in the framework of an equilibrium model to consider the propagation of shock waves in a gas-liquid foam with a highly nonuniform density distribution. A comparison of the numerical simulation and experimental studies reveals the basic features of the gasdynamic disturbances that arise in two-phase media of this kind. Zh. Tekh. Fiz. 67, 1–9 (November 1997)     

Review of theoretical gain-optimization studies in 10.6µm CO2-N2 gasdynamic lasers

A comprehensive theoretical analysis of optimization of gain in CO₂-N₂ gasdynamic laser employing wedge or conical or hyperbolic nozzles with either H₂O or He as the catalyst is presented. After a review of previous work, the usual governing equations for the steady inviscid quasi-one-dimensional flow in a supersonic nozzle of a gasdynamic laser are used to obtain similar solutions for the various flow quantities, which variables are subsequently used to optimize the small-signal gain on theP(20) line of the (001) → (100) transition of CO₂ at wavelength 10.6μm. The corresponding optimum values like reservoir pressure and temperature and nozzle area ratio also have been predicted and presented in the form of graphs. The analysis predicts that employing of 2D-wedge nozzle results in higher gain values and the CO₂-N₂-H₂O gasdynamic laser employing 2D-wedge nozzle is operationally the best laser system for which the optimum value as high as 3.1 m⁻¹ gain can be obtained.     

A generalized formulation for population distribution in a molecular laser

A generalized theoretical model for calculating the population distribution in a molecular laser is proposed. This molecule population is found to be quantized and depending upon temperature. In addition, we show, as a particular case, that population distribution in a diatomic gasdynamic laser arises from our model.     

Population of molecules as strongly anharmonic oscillators in a diatomic gasdynamic laser

Population distribution is studied quantitatively for a diatomic gasdynamic laser in which the molecules behave as strongly anharmonic oscillators under the action of a Morse internuclear potential. In fact, mathematical relationships concerning the two fundamental parameters associated with anharmonicity are derived.     

Lasers operating on cascade transitions of triatomic molecules

The general conditions necessary for the operation of gas lasers based on cascade vibrational-rotational transitions of molecules in the pulse-periodic regime are formulated. The features of such triatomic-molecule lasers with arbitrary excitation are discussed. A computation model is proposed for determining the energy characteristics (maximum attainable efficiency, average and relative lasing power, specific energy output) of free-flow cascade lasers. Systems are analyzed with various excitation methods: gasdynamic (including those with optical feedback), electric-discharge, and chemical (with the DF-CO₂ laser as the example). Practical recommendations with respect to the choice of mixture composition, optimum cavity lengths along the gas stream, and Q-switching frequency are made for the cascade lasers. A molecular gasdynamic laser emitting three wavelengths simultaneously is proposed.Quantum Radiophysics and Optics Division, Lebedev Physics Institute. Translated from Preprint No. 177 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1989     

Investigation of the dynamics of a laser-supported detonation wave using a self-consistent numerical model

Results are reported of a computational—theoretical analysis of the dynamics (propagation and decay) of laser-supported detonation waves (LSDW) in focused laser beams. The investigations were carried out using a self-consistent numerical model that takes account of the gasdynamic motion of the plasma and the refraction and absorption of the radiation in the plasma, with allowance for its real equation of state. An analysis is presented of the influence of the radial structure of the radiation on the propagation and decay of the LSDW, and of the conditions of the radiation transformation. Results on the dynamics of two-dimensional LSDW in the beam of an excimer laser are presented.Translated from Preprint No. IAE-5066/6 of the Kurchatov Atomic Energy Institute, Moscow, 1990.     

介质不均匀性对激光模式相位与光强分布的影响

将不均匀介质势函数进行泰勒展开,取其前3项近似,与描述光腔模式的亥姆霍兹方程中的特殊函数结合,根据光腔边界条件推导出光腔模式的本征解、激光输出功率以及不均匀介质与激光模式的相位与强度分布关系表达式。将表达式应用于氧碘化学激光器的功率与输出耦合率的非线性拟合以及近场光强分布的分析,预测趋势与文献结果相符。     

Investigations to the increase of the specific energy of a gasdynamic CO-laser

The input power density and hence the output power of electrically excited gasdynamic lasers is limited by instabilities of the glow discharge. The application of theoretical results, which have been obtained with respect of convection or flow lasers, to the discharge region of an electrically excited gasdynamic CO-laser shows, that especially thermal instabilities cause this glow collapse. An increased convection of local heat concentrations in front of the anode surface results in an improved stability behaviour. Input power densities of up to 100 W/cm³ are now accessible to operate the glow discharge and hence specific laser output powers of 57 kJ/kg are obtained.     

Gasdynamic CO laser with closed-cycle gas flow

The operation of an electrically excited gasdynamic CO laser with closed-cycle gas flow is described. Details of the gasdynamics, the recompression, and the cooling of the flowing gas are given. The electrical discharge produces contaminating gas compounds—in particular CO₂—which accumulate in the recirculating gas. The resulting transient behavior of the laser gas composition, the discharge characteristics, and the laser performance are studied and compared with the results obtained with the same CO laser in an open-flow system. It is found that the closed-cycle system may be operated for considerable time if the CO₂ contamination is removed from the laser gas.     

在固体透明材料中利用级联四波混频方法获得宽带多色飞秒激光脉冲的研究

飞秒激光光谱学实验研究的深入与拓展对飞秒激光脉冲的要求也越来越高.比如多色抽运探测实验需要同时用到多个不同频率的超短飞秒激光脉冲.本文设计了一个更加简单紧凑的实验装置,对两束不同中心频率的入射光引入相反啁啾,在厚度为0.5 mm的CaF2晶体中利用级联四波混频获得了光谱半高全宽近100nm,支持傅里叶转换极限脉宽小于10 fs的多色飞秒激光脉冲.这一结果将为拓展飞秒激光光谱学研究和应用发挥重要作用.     

Self-field effects on small-signal gain in two-stage free-electron lasers

Self-field effects, induced by charge and current densities of the electron beam, on gain in two-stage free-electron laser with nonuniform guide magnetic field is presented. The gain equation for small-signal has been derived analytically. The results of numerical calculations show a gain decrement for group I orbits and a gain enhancement for group II orbits, due to the self-field effects. The wiggler-induced self-magnetic field has a diamagnetic effect for group I orbits, whereas for group II, it has a paramagnetic effect. It is also found that using a nonuniform guide field, rather than a uniform one, causes the gain to increase.