Accession Number:

ADA222408

Title:

A Note on the Statistics of Laser Speckle

Descriptive Note:

Corporate Author:

MITRE CORP MCLEAN VA JASON PROGRAM OFFICE

Personal Author(s):

Report Date:

1990-03-01

Pagination or Media Count:

16.0

Abstract:

In considering eye protection we must take into account not only the average energy or average power density on the retina but also random variation, as noted by Fried 1981. Random variations can arise in at least two ways. Most surfaces, either natural or manmade, are extremely rough on the scale of an optical wavelength. Under illumination by coherent light, a wave reflected from a typical rough surface consists of contributions from many scattering points or areas. Images formed at a given point are the combination of amplitudes of spread functions, each arising from a different scattering point on the surface. The spread functions add with different phases, giving complex interference patterns, which are labeled speckle. The eyes will form a random intensity pattern on the retina subjective speckle. In a static, nonturbulent atmosphere, a speckle pattern propagates through the atmosphere unchanged it is statistically stationary. When turbulence is present, it seems to modulate the brightness of each speckle. Turbulence gives rise to a random, moving patchiness in the atmospheric temperature field and thus in the index of refraction. The combined effect of turbulent eddies to form a screen, which alters the phases of the waves that combined to form speckles. RH

Subject Categories:

  • Lasers and Masers

Distribution Statement:

APPROVED FOR PUBLIC RELEASE