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Proceedings Paper

Geometrical or Gaussian: where is that image anyway?
Author(s): Anthony S. Y. Lau
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Paper Abstract

For laser pointers and designators, far-field analyses based on geometrical optics or Fraunhofer diffraction are often inadequate and erroneous. To obtain useful results, we must apply Fresnel’s diffraction theory, but at the cost of having to abandon a traditional way of defining “focus,” as well as having to invent a new depth-of-focus formula. One consequence of Fresnel analysis is that we may “ray trace” Gaussian beams. Gaussian-beam ray trace is similar to geometric ray trace, but it leads to radically different results that often confound common sense. This paper begins with examples of systems in which geometric and Fraunhofer analyses fail, demonstrates how Fresnel analysis applies, points out the need for precise definitions of focus and depth of focus, and ends with some simple rules of thumb based on wave front aberrations and the characteristic Fresnel number.

Paper Details

Date Published: 1 July 1992
PDF: 13 pages
Proc. SPIE 10263, Lens Design: A Critical Review, 102630F (1 July 1992); doi: 10.1117/12.131978
Show Author Affiliations
Anthony S. Y. Lau, Hughes Aircraft Co. (United States)

Published in SPIE Proceedings Vol. 10263:
Lens Design: A Critical Review
Warren J. Smith, Editor(s)

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