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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:Statistical properties and giant fluctuations for
laser beam propagating in a turbulent medium - Pav
el Lushnikov (University of New Mexico)
DTSTART;TZID=Europe/London:20220714T160000
DTEND;TZID=Europe/London:20220714T163000
UID:TALK175892AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/175892
DESCRIPTION:A statistical properties of a laser beam propagati
ng in a turbulent medium\nare studied. It is prove
n that the intensity fluctuations at large\npropag
ation distances possess a Gaussian probability den
sity function and\nestablish quantitative criteria
for realizing the Gaussian statistics\ndepending
on the laser propagation distance\, laser beam wai
st\, laser\nfrequency\, and turbulence strength. W
e calculate explicitly the laser\nenvelope pair co
rrelation function and corrections to its higher-o
rder\ncorrelation functions breaking Gaussianity.
At intermediate distances the\nlaser intensity flu
ctuations follows the Poisson distribution (i.e. t
he\namplitudes satisfies the Gaussian statistics)
while the tail is strongly\nnon-Gaussian with squa
re-root dependence on the intensity in the exponen
t.\nThe transition between the Poisson distributio
n and the non-Gaussian tail\noccurs at the values
of intensity which quickly increases with the\npro
pagation distance. We find the explicit analytic e
xpression for the\nfourth order correlation functi
on vs. propagation distance and the\nturbulence st
rength which is determined by non-Gaussian tails.
We finds\nthat this correlation function is in exc
ellent agreement with the large\nscale supercomput
er simulations of laser wave propagation. We discu
ss also\nstatistical properties of the brightest s
pots in the speckle pattern and\nfind that the mos
t intense speckle approximately preserves both the
\nGaussian shape and the diameter of the initial c
ollimated beam while\nloosing energy during propag
ation. After propagating 7km through\ntypical atmo
spheric conditions\, approximately one in one thou
sand of\natmospheric realizations produces an inte
nse speckle with 20-30\\% of the\ninitial power. S
uch optimal atmospheric realizations create an eff
ective\nlens which focuses the intense speckle bey
ond the diffraction limit of\nthe propagation in v
acuum.
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:
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