Aerosol-induced limitations on the propagation of high power laser beams

Autric, M.; Lefauconnier, C.; Vigliano, P.; Dufresne, D.; Bournot, Philippe

doi:10.2514/6.1987-1454

Cited by 2 publications

(2 citation statements)

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“…Onset of the breakdown process on the aerosol first of all needs the exceeding ofan energy density barrier (J/cm2), which corresponds to the vaporization threshold of materials of the constituent elements of air and then the passing of an intensity threshold (W/cm2) which is the breakdown threshold. The latter decreases with radiation wavelength, optical diameter of the aerosol and laser pulse duration ; it depends little on the material (1)(2)(3)(4)(5)(6)(7)(8)(9). It is clear that the transmitted energy ratio depends on the number of aerosols present in the beam path and their dimensional distribution.…”

Section: Experimental Arrangementmentioning

confidence: 95%

Study Of The Propagation Of A High Power Infrared Laser Beam Through The Atmosphere. Influence Of Meteorological Conditions

et al. 1989

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Propagation through the atmosphere of a high power laser beam is limited by gaseous and particulate extinction and above all by optical breakdown induced by aerosols with relatively low intensity thresholds. The plasma created strongly absorbs the incident laser radiation and thus limits the maximum energies transmitted behind the breakdown zone.The object of this paper is to study breakdown thresholds in terms of energy density and incident intensity as well as transmission ratios of a CO2 laser beam as a function of natural atmospheric conditions. The setting up of an automatic station for meteorological and fine granulometric measurements enabled us to know the state of the atmosphere over the first ten meters of the surface boundary layer at each moment during laser shots. Five kinds of characteristic situation from the meteorological point of view with visibility greater than 5 km was studied : A -cold anticyclone conditions with the approach of an atmospheric disturbance B -humid low pressure conditions C-disturbed conditions : rain and drizzle D-maritime and continental wind conditions E-breaking wave sea -state simulation with criteria of similarity.The analysis was carried out in two steps. The first consisted in correlating the variations in meterological parameters and those of the granulometry of the atmospheric aerosol. The second step linked the granulometric fluctuations to the variations in breakdown threshold and transmission ratios.Intensity and fluence thresholds from 70 -90 MW /cm2 ; 2 -4 J /cm2 up to 150 -160 MW /cm2 ; 6,5 -7,5 J /cm2 have been measured for these different conditions.Comparing the best transmission ratios obtained in a cleaned atmosphere with the worst in strongly breaking sea conditions, we have obtained for 62 J /cm2, energy transmission of 90 % and 40 % respectively and 25 % to 15 % for 250 J /cm2.

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Section: Experimental Arrangementmentioning

confidence: 95%

Study Of The Propagation Of A High Power Infrared Laser Beam Through The Atmosphere. Influence Of Meteorological Conditions

et al. 1989

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“…18) Phase compensation for thermal blooming leads to a phase compensated instability (PCI). Its growth rate depends on the actuator spacing (LXX) with a Fresnel number, Na (LX)2/AL, and is given by…”

Section: Atmospheric Thermal Bloomingmentioning

confidence: 99%

Atmospheric thermal blooming and beam clearing by aerosol vaporization

Krapchev

1990

SPIE Proceedings

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Thermal blooming limits the HEL power transmitted through the atmosphere at a given beam diameter. The role of refractive index and velocity turbulence has been studied.When the absorption is due to the aerosols, one can reduce the blooming by vaporizing the particles and clearing the beam path. Atmospheric Thermal BloomingIn this section the thermal blooming theory is outlined and the quantities of interest to the atmospheric propagation of a HEL are defined. The calculation includes the effect of the finite beam size. This approach is used for the first time and it allows to evaluate the steady state when t > D/Vw. The mutual coherence function, the Strehi ratio and the critical power are evaluated for a constant wind and for an isotropic wind turbulence model.These models represent the worst and best case scenarios. In the case of the unrealistic constant wind model, one can propagate little HEL power iii a given beam aperture. The results are so pessimistic that one can not build a GBL for BMD applications. Typically, one can transmit only a few MW of HEL power with a beam director of a few meters in diameter. In the case of turbulent wind, one can propagate 100 MW at beam apertures of a few meters. The latter model of the atmosphere is more realistic and we shall base on it our estimates of the system's performance. An intermediate case of constant wind and beam slew is of interest for propagation to low earth orbits. In that case one can transmit tens of MW with beam diameters of a few meters.The wave equation for the laser field is written in the paraxial approximation1 iO2E + VE + kSnE = 0 ,where k is the laser wavenumber and 6ri is the change in refractive index, Sn 872T + STill. S?2T iS the contribution from turbulence. It is a random quantity determined by the two point correlation function with a Kolmogorov spectrum,(2) (SnT(rl)öflT(r2)) = 0.033C f 'exp{ii -F2)] . (1.2) SPIE Vol. 1221 Propagation of High-Energy Laser Beams through the Earth's Atmosphere (1990)1 91 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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Aerosol-induced limitations on the propagation of high power laser beams

Cited by 2 publications

References 15 publications

Study Of The Propagation Of A High Power Infrared Laser Beam Through The Atmosphere. Influence Of Meteorological Conditions

Study Of The Propagation Of A High Power Infrared Laser Beam Through The Atmosphere. Influence Of Meteorological Conditions

Atmospheric thermal blooming and beam clearing by aerosol vaporization

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