Log-Amplitude Mean for Laser-Beam Propagation in the Atmosphere
JOSA, Vol. 59, Issue 9, pp. 1139-1148 (1969)
http://dx.doi.org/10.1364/JOSA.59.001139
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Abstract
An integral expression is evaluated for the log-amplitude mean value of a gaussian or laser-like optical beam propagating along a horizontal path in a turbulent atmosphere. The mean-value integral expression has been taken from an analysis by Schmeltzer for a gaussian beam in the atmosphere. The expressions presented here for the log-amplitude mean value depend on the product of a strength factor, which is the log-amplitude variance for a point source, and a multiplying factor that depends on the source beam size. Numerical results for the beam-size-dependent factor are given for a wide range of beam sizes, wavelengths, and path lengths. Numerical results are also presented for the mean on-axis irradiance and mean beam size, for focused and collimated gaussian beams. These will find application in the design of systems for laser communication in the atmosphere. The data are obtained by combining our results for the log-amplitude mean with published data for the variance. The integral expression used here for the log-amplitude mean value is based on an assumption which restricts the range of validity of our results. The conditions necessary for its validity are discussed.
© 1969 Optical Society of America
Citation
F. G. GEBHARDT and S. A. COLLINS, JR., "Log-Amplitude Mean for Laser-Beam Propagation in the Atmosphere," J. Opt. Soc. Am. 59, 1139-1148 (1969)
http://www.opticsinfobase.org/josa/abstract.cfm?URI=josa-59-9-1139
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References
- V. I. Tatarski, Wave Propagation in a Turbulent Medium, transl. R. A. Silverman (McGraw—Hill Book Co., New York, 1961).
- L. A. Chernov, Wave Propagation in a Random Medium, transl. R. A. Silverman (McGraw—Hill Book Co., New York, 1960).
- Reference 1, Chap. 9.
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- As implied by our sign convention for R in Eq. (2.1), we are assuming e^{iwt} time dependence. It should be noted that this sign convention for R differs from that used by Schmeltzer [Ref. 6, Eq. (2.1)]. Also, it should be noted that the time convention in Ref. 6, p. 340 is stated to be e^{iwt} but the mathematical formulation actually follows e^{-iwt} time dependence, as can be readily determined from Eqs. (2.6) and (2.12) of the same reference.
- Equation (2.2) is obtained from Sckmeltzer's Eq. (7.6) by taking the real part of the right-hand side and setting s=z_{0} and q=s in the second term.
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- Equation (4.11) is obtained from Eq. (4.11) in Ref. 7 by using the relationships Γ(l/6) and Re(i^{5/6}) = cos(5π/12). Equation (4.11) is obtained from Eq. (4.11) in Ref. 7 by using the relationships Ggr;(-5/6) = -(6/5) Γ(l/6) and Re(i^{5/6}) = cos(5π/12).
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- A gaussian mean beam shape is assumed here for the atmospherically perturbed laser beam because of the lack of available data for the log-amplitude statistics at off-axis points in the beam. For a randomly wandering gaussian-irradiance distribution, the average beam pattern can be shown to be gaussian when the orthogonal displacements Δx, Δy of the beam center are independent normal-random variables, with zero means and equal variances. Under more general conditions, however, (e.g., when the perturbed gaussian-beam pattern is also distorted) the average beam shape may not be gaussian.
- Reference 1, p. 140.
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