Abstract

The extinction coefficients of laboratory generated fog at 0.63 and 10.6 μm are monitored during and after passage of a coaxial CO2 laser pulse of 2-J/cm2 fluence. Pulse passage causes a slight decrease in extinction at 10.6 μm and a marked increase in this quantity at 0.63 μm. This effect is consistent with the significant reduction in fog droplet size, caused by absorption of energy from the pulse. The data are analyzed to provide the time dependence of particle size following pulse passage, and the inferred particle growth rate is consistent with the mechanism of recondensation, onto droplets which survive the pulse passage, of water vapor driven from the fog droplets by absorption of pulse energy. For any aerosol whose particle size is significantly altered by laser pulse passage, the effect of the pulse on light extinction is determined by initial aerosol particle size and index of refraction as well as the wavelength of the light to be transmitted.

© 1983 Optical Society of America

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References

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  1. G. J. Mullaney, W. H. Christiansen, D. A. Russell, Appl. Phys. Lett. 13, 145 (1968).
    [CrossRef]
  2. M. C. Fowler, J. R. Dunphy, D. C. Smith, “Laser Propagation Experiments-Aerosol and Stagnation Zone Effects,” UTRC Report R77-922578-13 (1977), p. B41.
  3. J. E. Lowder, H. Kleiman, R. W. O'Neil, J. Appl. Phys. 45, 221 (1974).
    [CrossRef]
  4. P. Kafalas, A. P. Ferdinand, Appl. Opt. 12, 29 (1973).
    [CrossRef] [PubMed]
  5. P. Kafalas, J. Herrmann, Appl. Opt. 12, 772 (1973).
    [CrossRef] [PubMed]
  6. M. C. Fowler, United Technologies;unpublished.
  7. T. S. Chu, IEEE J. Quantum Electron. QE-3, 254 (1967).
    [CrossRef]
  8. A. J. Cantor, “A Mie Scattering Computer Program,” United Technologies Report UTRC-28 (1977).
  9. J. Wallace, “Formulation of the Analysis for Nonlinear Aerosol Thermal Blooming,” Far Field, Inc., 1981.
  10. N. H. Fletcher, The Physics of Rainclouds (Cambridge U.P., 1962), pp. 122–127.
  11. H. C. Van de Hulst, Light Scattering by Small Particles (Wiley, New York, 1957), p. 176.
  12. Ref. 11, p. 179.

1974

J. E. Lowder, H. Kleiman, R. W. O'Neil, J. Appl. Phys. 45, 221 (1974).
[CrossRef]

1973

1968

G. J. Mullaney, W. H. Christiansen, D. A. Russell, Appl. Phys. Lett. 13, 145 (1968).
[CrossRef]

1967

T. S. Chu, IEEE J. Quantum Electron. QE-3, 254 (1967).
[CrossRef]

Cantor, A. J.

A. J. Cantor, “A Mie Scattering Computer Program,” United Technologies Report UTRC-28 (1977).

Christiansen, W. H.

G. J. Mullaney, W. H. Christiansen, D. A. Russell, Appl. Phys. Lett. 13, 145 (1968).
[CrossRef]

Chu, T. S.

T. S. Chu, IEEE J. Quantum Electron. QE-3, 254 (1967).
[CrossRef]

Dunphy, J. R.

M. C. Fowler, J. R. Dunphy, D. C. Smith, “Laser Propagation Experiments-Aerosol and Stagnation Zone Effects,” UTRC Report R77-922578-13 (1977), p. B41.

Ferdinand, A. P.

Fletcher, N. H.

N. H. Fletcher, The Physics of Rainclouds (Cambridge U.P., 1962), pp. 122–127.

Fowler, M. C.

M. C. Fowler, United Technologies;unpublished.

M. C. Fowler, J. R. Dunphy, D. C. Smith, “Laser Propagation Experiments-Aerosol and Stagnation Zone Effects,” UTRC Report R77-922578-13 (1977), p. B41.

Herrmann, J.

Kafalas, P.

Kleiman, H.

J. E. Lowder, H. Kleiman, R. W. O'Neil, J. Appl. Phys. 45, 221 (1974).
[CrossRef]

Lowder, J. E.

J. E. Lowder, H. Kleiman, R. W. O'Neil, J. Appl. Phys. 45, 221 (1974).
[CrossRef]

Mullaney, G. J.

G. J. Mullaney, W. H. Christiansen, D. A. Russell, Appl. Phys. Lett. 13, 145 (1968).
[CrossRef]

O'Neil, R. W.

J. E. Lowder, H. Kleiman, R. W. O'Neil, J. Appl. Phys. 45, 221 (1974).
[CrossRef]

Russell, D. A.

G. J. Mullaney, W. H. Christiansen, D. A. Russell, Appl. Phys. Lett. 13, 145 (1968).
[CrossRef]

Smith, D. C.

M. C. Fowler, J. R. Dunphy, D. C. Smith, “Laser Propagation Experiments-Aerosol and Stagnation Zone Effects,” UTRC Report R77-922578-13 (1977), p. B41.

Van de Hulst, H. C.

H. C. Van de Hulst, Light Scattering by Small Particles (Wiley, New York, 1957), p. 176.

Wallace, J.

J. Wallace, “Formulation of the Analysis for Nonlinear Aerosol Thermal Blooming,” Far Field, Inc., 1981.

Appl. Opt.

Appl. Phys. Lett.

G. J. Mullaney, W. H. Christiansen, D. A. Russell, Appl. Phys. Lett. 13, 145 (1968).
[CrossRef]

IEEE J. Quantum Electron.

T. S. Chu, IEEE J. Quantum Electron. QE-3, 254 (1967).
[CrossRef]

J. Appl. Phys.

J. E. Lowder, H. Kleiman, R. W. O'Neil, J. Appl. Phys. 45, 221 (1974).
[CrossRef]

Other

A. J. Cantor, “A Mie Scattering Computer Program,” United Technologies Report UTRC-28 (1977).

J. Wallace, “Formulation of the Analysis for Nonlinear Aerosol Thermal Blooming,” Far Field, Inc., 1981.

N. H. Fletcher, The Physics of Rainclouds (Cambridge U.P., 1962), pp. 122–127.

H. C. Van de Hulst, Light Scattering by Small Particles (Wiley, New York, 1957), p. 176.

Ref. 11, p. 179.

M. C. Fowler, J. R. Dunphy, D. C. Smith, “Laser Propagation Experiments-Aerosol and Stagnation Zone Effects,” UTRC Report R77-922578-13 (1977), p. B41.

M. C. Fowler, United Technologies;unpublished.

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Figures (7)

Fig. 1
Fig. 1

Schematic of apparatus.

Fig. 2
Fig. 2

(a) Spatial distribution of transmitted pulse fluence with the cell empty, J0, and filled with fog, J. (b) Spatial distribution of ∊l, equal to In(J0/J), using the data of (a), and J0, showing the pulse fluence's ability to decrease on the time scale of the pulse width, 2 μsec.

Fig. 3
Fig. 3

Time history of transmitted probe beam power. Passage of the laser pulse decreases opacity of fog at 10.6 μm but increases it at 0.63 μm.

Fig. 4
Fig. 4

Oscillogram of transmitted He–Ne probe beam power. At no time does ∊l decrease below its prepulse value but rises to a maximum in 35 msec and returns to its prepulse value in 100 msec as convection moves fresh unirradiated fog into the probe beam.

Fig. 5
Fig. 5

Extinction coefficient ratio vs r ̅. The dots are the values calculated using the code of Ref. 8, and the fine structure oscillations are interpolated using the formula found in Ref. 11.

Fig. 6
Fig. 6

Time dependence of effective droplet radius. Open circles represent data from Fig. 3; closed circles represent data from Fig. 4. The horizontal arrow denotes r ̅ for unperturbed fog. The vertical arrow denotes time of onset for buoyancy driven convective cleanout of probe beam.

Fig. 7
Fig. 7

Functions (t) from the Fig. 4 data and ∊c(r) calculated from Eq. (3) for C = 0.082 g/m3. The square is the prepulse value of and r ̅. The straight line is calculated from Eq. (1) with S calculated using this value of C and neglecting a/r.

Equations (3)

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d σ d t = 2 π G ( S a / r ) ,
C = 4 3 π r ̅ 3 ρ L ,
c ( r ̅ ) = 3 C σ / 4 π r ̅ 3 ρ L .

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