Affiliation:
1. Naval Surface Warfare Center Dahlgren Division
Abstract
In this paper, an approach for detecting branch points using a
Shack–Hartmann wavefront sensor (SHWFS) is introduced. Simulated data
are created using Monte Carlo wave-optics simulations of varying
turbulence strengths. It is assumed that the presence of a branch
point in the SHWFS subaperture lenslet pupils causes appreciable beam
spreading in the image plane. Therefore, second-moment statistics are
used to quantify beam spread for each subaperture image-plane
irradiance pattern. Thresholding is then employed to dictate what
degree of beam spreading is sufficient to determine the presence of a
branch point. Three different thresholds are imposed: liberal,
moderate, and conservative. Furthermore, the collected SHWFS signal is
treated as analog, digitized, and digitized with three levels of
additive noise: low, moderate, and high. Monte Carlo simulations are
conducted for 20 different spherical-wave Rytov numbers (RSW) ranging from 0.1 to 2.0. It was
found that when conservative thresholds were employed, for the analog
signal, digitized signal with no noise, and digitized signal with low
noise, the percent of detections mostly comprised actual branch
points, and false-positive detections were largely minimized. For the
liberal thresholding cases, many false-positives were detected for all
SHWFS signal types; however, significantly more branch points were
also detected. The results presented in this paper are encouraging,
and such results will inform efforts to develop branch-point tolerant
least-squares reconstructors or use a SHWFS for optical-turbulence
characterization in high-RSW environments.
Subject
Atomic and Molecular Physics, and Optics,Engineering (miscellaneous),Electrical and Electronic Engineering
Cited by
8 articles.
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