# Beam expanders

Contributor: Stas Fainer

This is a simulation of two types of beam expanders - Keplerian beam expander, and Galilean beam expander. A beam expander expands or reduces the diameter of a beam of collimated light. A Galilean beam expander is composed of a convex and a concave lens, whereas a Keplerian beam expander is composed of two convex lenses. In both types, the sum of the lenses' focal length equals their separation distance.

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