Formation and experimental investigation of a gaseous disperse medium of a pulsed chemical H<sub>2</sub>— F<sub>2</sub>laser initiated by IR radiation

Azarov, Michail A.; Дроздов, В. А.; Igoshin, Valerii I; Kurov, A Yu; Petrov, A L; Pichugin, S Yu; Troshchinenko, Georgiy A.

doi:10.1070/qe1997v027n11abeh001099

Cited by 7 publications

(7 citation statements)

References 3 publications

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“…The source of radiation is provided by a pulsed chemical HF laser with the following characteristics [10]: t i = 2.6 µs, λ = 4.2 µm, R = 5 mm, and Θ = 1.5 µs. The thermal and optical properties of particles with due regard for their temperature dependence are found from the respective handbooks.…”

Section: Calculation Resultsmentioning

confidence: 99%

“…The time variation of the pulse is simulated by a continuous piecewise-linear function constructed on the basis of characteristics of a real system [10]. The function simulating the piecewise linear-dependence of laser pulse intensity on time for a system of points t 1 , …, t N with values at the points of F 1 , … F N is written as…”

Section: Model Of Laser Pulsementioning

confidence: 99%

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Calculation of the Threshold Power of Optical Breakdown during Interaction between a Laser Pulse and Droplets of Dielectric Liquid

Волков

Emel’yanov

2005

High Temp

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A mathematical model is developed of optical breakdown on droplets of dielectric liquid under the effect of pulsed laser radiation. The heating and evaporation of a particle, and the generation of a vapor halo and its ionization, as well as the propagation of shock waves in the space surrounding the particle, are treated as separate stages of the process. The threshold characteristics of the laser beam parameters are determined, which are sufficient for the initiation of optical breakdown on droplets of dielectric liquid. The dependence of the threshold power of optical breakdown on the size of laser spot is calculated.

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Section: Calculation Resultsmentioning

confidence: 99%

Section: Model Of Laser Pulsementioning

confidence: 99%

Calculation of the Threshold Power of Optical Breakdown during Interaction between a Laser Pulse and Droplets of Dielectric Liquid

Волков

Emel’yanov

2005

High Temp

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“…As a radiator, we use a pulsed chemical HF laser having the following characteristics [11]: t i = 2.6 µsec; λ = 4.2 µm; R = 1.5 cm; θ = 1.5 µsec. The thermophysical and optical properties of particles were taken from reference books with allowance for their temperature dependence.…”

Section: Gas-dynamic Processes In the Vapor Aureolementioning

confidence: 99%

“…The change in the pulse intensity with time is modeled by the continuous piecewise-linear function formed on the basis of the real system characteristics [11]. The function modeling the piecewise-linear time dependence of the laser-pulse intensity is written on the system of points t 1 , ..., t N with values F 1 , ..., F N as…”

mentioning

confidence: 99%

Determination of the optical-breakdown threshold under irradiation of condensed inclusions by pulsed laser radiation

Волков

Emel’yanov

2005

J Eng Phys Thermophys

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On the basis of the thermal approach, a mathematical model of the optical breakdown on condensed inclusions exposed to pulsed laser radiation is developed. As individual stages of the process, we consider the particle heating and evaporation, the formation of a vapor aureole and its ionization, as well as the propagation of shock waves in the space surrounding the particle. The threshold characteristics of the laser-beam parameters sufficient for initiating an optical breakdown on metal and dielectric particles, as well as on dielectric liquid drops are determined.The presence of particles having fairly low values of the vaporization temperature and ionization potential leads to a decrease in the threshold values of the optical breakdown compared to the breakdown threshold in a pure gas [1,2]. The search for conditions under which a decrease in the threshold value of the laser-pulse intensity is possible is of interest for both laser initiation of processes and radiation transportation through explosive mixtures.To construct a model of the laser-radiation interaction with a particle, the explosive and thermal approaches are used. In the first approach, the particle, being inertially attached, during a pulse manages to absorb energy sufficient for its complete evaporation. At high energy concentrations, the particle is heated so fast that the condensedphase substance acquires the parameters of the overheated metastable state and passes to vapor by way of explosion. The thermal approach is based on a more detailed consideration of such elements of the processes as heating, evaporation, and ionization of the vapor cloud.The role of explosive evaporation in the decrease in the optical breakdown threshold is discussed in [3]. For solid particles the breakdown mechanisms are realized in the material vapors at T , 10 4 K. For water droplets with r p = 50-200 µm the process of explosive evaporation proceeds at lower temperatures T v , 10 3 K. As a mechanism initiating optical discharge, the shock waves resulting from the droplet expansion and the high pressure inside it (p >10 3 atm) are considered.In [4], the explosive mechanism of the laser-radiation interaction with a water droplet is described. Rather long pulses (t i ≤ 300 µsec) and comparatively large drops (r p = 100-200 µm) at Q , 1 J are considered. The explosive evaporation of the droplet is explained by the appearance and growth inside it of vapor bubbles when the liquid temperature reaches the value of the explosive boiling temperature (for water at normal pressure it is equal to 578 K). In [5], the following reasons for the decrease in the breakdown threshold to the values of I * = 10 7 -10 8 W/cm 2 in the presence of water droplets are considered: 1. The thermal explosion of the particle, the condition for which is the absorption by the particle of energy exceeding the heat of its evaporation in a time shorter than the time of travel of sound through its cross section.2. The thermal ionization of the gas on the shock wave arising from the particle explosion...

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“…The first experimental results to achieve a photonbranched chain reaction in a two-phase medium were published in [10]. The authors showed that during the injection of a fine-disperse aluminum powder with particle diameters of 0.3 μm covered by thin oxide film into a mixture of F 2 + H 2 + O 2 + He, the system remains stable.…”

Section: Introductionmentioning

confidence: 99%

Laser-Induced Photon-Branched Chain Reaction in a Chemically-Active Gas-Dispersed Medium

2008

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A promising avenue in the development of high-energy pulsed chemical HF/DF lasers and amplifiers is the utilization of a photon-branched chain reaction initiated in a two-phase active medium, that is, a medium containing a laser working gas and ultradispersed passivated metal particles. These particles are evaporated under the action of IR laser radiation which results in the appearance of free atoms, their diffusion into the gas, and the development of a photon-branching chain process, which involves photons as both reactants and products. The key obstacle here is the formation of a relatively large volume (in excess of103 cm3) of the stable active medium and filling this volume homogeneously for a short time with a submicron monodisperse metal aerosol, which has specified properties. In this paper, results are presented for an extensive study of laser initiation of a photon-branched chain reaction in a gas-dispersedH2–F2medium.

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Formation and experimental investigation of a gaseous disperse medium of a pulsed chemical H₂— F₂laser initiated by IR radiation

Cited by 7 publications

References 3 publications

Calculation of the Threshold Power of Optical Breakdown during Interaction between a Laser Pulse and Droplets of Dielectric Liquid

Calculation of the Threshold Power of Optical Breakdown during Interaction between a Laser Pulse and Droplets of Dielectric Liquid

Determination of the optical-breakdown threshold under irradiation of condensed inclusions by pulsed laser radiation

Laser-Induced Photon-Branched Chain Reaction in a Chemically-Active Gas-Dispersed Medium

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Formation and experimental investigation of a gaseous disperse medium of a pulsed chemical H2— F2laser initiated by IR radiation

Cited by 7 publications

References 3 publications

Calculation of the Threshold Power of Optical Breakdown during Interaction between a Laser Pulse and Droplets of Dielectric Liquid

Calculation of the Threshold Power of Optical Breakdown during Interaction between a Laser Pulse and Droplets of Dielectric Liquid

Determination of the optical-breakdown threshold under irradiation of condensed inclusions by pulsed laser radiation

Laser-Induced Photon-Branched Chain Reaction in a Chemically-Active Gas-Dispersed Medium

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Formation and experimental investigation of a gaseous disperse medium of a pulsed chemical H₂— F₂laser initiated by IR radiation