Geometrical or Gaussian: where is that image anyway?

Anthony S. Y. Lau

doi:10.1117/12.131978

1 July 1992 Geometrical or Gaussian: where is that image anyway?

Anthony S. Y. Lau

Proceedings Volume 10263, Lens Design: A Critical Review; 102630F (1992) https://doi.org/10.1117/12.131978
Event: OE/LASE '92, 1992, Los Angeles, CA, United States

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.

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Anthony S. Y. Lau "Geometrical or Gaussian: where is that image anyway?", Proc. SPIE 10263, Lens Design: A Critical Review, 102630F (1 July 1992); https://doi.org/10.1117/12.131978

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KEYWORDS

Ray tracing

Diffraction

Failure analysis

Far-field diffraction

Gaussian beams

Geometrical optics

Laser designators

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