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SUMMARY:Statistical properties and giant fluctuations for laser beam propa
 gating in a turbulent medium - Pavel Lushnikov (University of New Mexico)
DTSTART:20220714T150000Z
DTEND:20220714T153000Z
UID:TALK175892@talks.cam.ac.uk
DESCRIPTION:A statistical properties of a laser beam propagating in a turb
 ulent medium\nare studied. It is proven that the intensity fluctuations at
  large\npropagation distances possess a Gaussian probability density funct
 ion and\nestablish quantitative criteria for realizing the Gaussian statis
 tics\ndepending on the laser propagation distance\, laser beam waist\, las
 er\nfrequency\, and turbulence strength. We calculate explicitly the laser
 \nenvelope pair correlation function and corrections to its higher-order\n
 correlation functions breaking Gaussianity. At intermediate distances the\
 nlaser intensity fluctuations follows the Poisson distribution (i.e. the\n
 amplitudes satisfies the Gaussian statistics) while the tail is strongly\n
 non-Gaussian with square-root dependence on the intensity in the exponent.
 \nThe transition between the Poisson distribution and the non-Gaussian tai
 l\noccurs at the values of intensity which quickly increases with the\npro
 pagation distance. We find the explicit analytic expression for the\nfourt
 h order correlation function vs. propagation distance and the\nturbulence 
 strength which is determined by non-Gaussian tails. We finds\nthat this co
 rrelation function is in excellent agreement with the large\nscale superco
 mputer simulations of laser wave propagation. We discuss also\nstatistical
  properties of the brightest spots in the speckle pattern and\nfind that t
 he most intense speckle approximately preserves both the\nGaussian shape a
 nd the diameter of the initial collimated beam while\nloosing energy durin
 g propagation. After propagating 7km through\ntypical atmospheric conditio
 ns\, approximately one in one thousand of\natmospheric realizations produc
 es an intense speckle with 20-30\\% of the\ninitial power. Such optimal at
 mospheric realizations create an effective\nlens which focuses the intense
  speckle beyond the diffraction limit of\nthe propagation in vacuum.
LOCATION:Seminar Room 1\, Newton Institute
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