Abstract

Thermal blooming is analyzed by using a wave-propagation code to determine the speed of response of the blooming effect to changes in the transmitted laser beam. Results are developed to indicate where along the propagation path the dominant part of the thermal-blooming effects arise. It is found that most of the effect arises within about two times the depth of focus of the target, where the beam diameter is small. This suggests, and the time-dependent propagation results confirm, that the time constant descriptive of the speed of response of thermal blooming is proportional to the time it takes a parcel of air to move across the beam width in the depth-of-focus region.

© 1982 Optical Society of America

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References

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  1. C. B. Hogge, “Adaptive optics in high energy laser systems,” in Adaptive Optics and Short Wavelength Sources, S. F. Jacobs, M. Sargent, and M. O. Scully, eds. (Addison-Wesley, Reading, Mass., 1978).
  2. J. N. Hayes, P. B. Ulrich, and A. H. Aitken, “Effects of the atmosphere on the propagation of 10.6-μ laser beams,” Appl. Opt. 11, 257–260 (1972).
    [Crossref] [PubMed]
  3. F. G. Gebhardt and D. C. Smith, “Self-induced thermal distortion in the near field for a laser beam in a moving medium,” IEEE J. Quantum Electron. QE-7, 63–73 (1971).
    [Crossref]
  4. D. L. Fried, ed., J. Opt. Soc. Am. 67, 269–422 (1977) (special issue on adaptive optics).
    [Crossref]

1977 (1)

1972 (1)

1971 (1)

F. G. Gebhardt and D. C. Smith, “Self-induced thermal distortion in the near field for a laser beam in a moving medium,” IEEE J. Quantum Electron. QE-7, 63–73 (1971).
[Crossref]

Aitken, A. H.

Gebhardt, F. G.

F. G. Gebhardt and D. C. Smith, “Self-induced thermal distortion in the near field for a laser beam in a moving medium,” IEEE J. Quantum Electron. QE-7, 63–73 (1971).
[Crossref]

Hayes, J. N.

Hogge, C. B.

C. B. Hogge, “Adaptive optics in high energy laser systems,” in Adaptive Optics and Short Wavelength Sources, S. F. Jacobs, M. Sargent, and M. O. Scully, eds. (Addison-Wesley, Reading, Mass., 1978).

Smith, D. C.

F. G. Gebhardt and D. C. Smith, “Self-induced thermal distortion in the near field for a laser beam in a moving medium,” IEEE J. Quantum Electron. QE-7, 63–73 (1971).
[Crossref]

Ulrich, P. B.

Appl. Opt. (1)

IEEE J. Quantum Electron. (1)

F. G. Gebhardt and D. C. Smith, “Self-induced thermal distortion in the near field for a laser beam in a moving medium,” IEEE J. Quantum Electron. QE-7, 63–73 (1971).
[Crossref]

J. Opt. Soc. Am. (1)

Other (1)

C. B. Hogge, “Adaptive optics in high energy laser systems,” in Adaptive Optics and Short Wavelength Sources, S. F. Jacobs, M. Sargent, and M. O. Scully, eds. (Addison-Wesley, Reading, Mass., 1978).

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Figures (3)

Fig. 1
Fig. 1

(a) Thermal blooming for uniform wind as a function of screen position; the normalized intensity is P(x)/P0, whereas the fractional path length is x. (b) Thermal blooming for a slued beam as a function of screen position.

Fig. 2
Fig. 2

(a) Cumulative thermal blooming for a uniform wind; results are accumulated from the target plane back to the transmitter according to Eq. (3). The normalized intensity product is (x). (b) Cumulative thermal blooming for a slued beam. Results are accumulated from the target plane back to the transmitter according to Eq. (3).

Fig. 3
Fig. 3

Time dependence of thermal blooming for uniform wind. Results are calculated for = 10 Fresnel number and for HEL power levels resulting in thermal-blooming reductions in the peak-power density at the target of 0.5, 0.4, 0.3, and 0.2 of the diffraction-limited value. Time is normalized by dividing by TU, as defined by Eq. (5).

Equations (7)

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F = D 2 / ( λ R )
L = 2 R / F .
P ( x ) = exp { d x ln [ P ( x ) / P 0 ] } .
d = D / F .
T U = d / V = D F V ,
T S = d / ( ω R ) = D F ω R .
τ = 0.2 T