Homogenization with coherent light illuminated beam shaping diffusers for vision applications

spatial resolution limited by speckle pattern

Bence Kondász, B. Hopp, T. Smausz

Research output: Contribution to journalArticle

Abstract

Background: Homogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications. Experimental: Two diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams. Results: The intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination. Conclusion: As an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.

Original languageEnglish
Article number27
JournalJournal of the European Optical Society
Volume14
Issue number1
DOIs
Publication statusPublished - Dec 1 2018

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diffusers
coherent light
speckle patterns
homogenizing
light beams
spatial resolution
homogeneity
fibers
angular resolution
CMOS
light sources
apertures
illumination
requirements
output
high resolution
sensors
scattering
lasers

Keywords

  • Beam homogenization
  • Beam shaping diffuser
  • Speckle pattern

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

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abstract = "Background: Homogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications. Experimental: Two diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams. Results: The intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination. Conclusion: As an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.",
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AU - Kondász, Bence

AU - Hopp, B.

AU - Smausz, T.

PY - 2018/12/1

Y1 - 2018/12/1

N2 - Background: Homogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications. Experimental: Two diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams. Results: The intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination. Conclusion: As an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.

AB - Background: Homogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications. Experimental: Two diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams. Results: The intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination. Conclusion: As an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.

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