As shown in the main body of the text, many infrared systems require devices that scan the instantaneous field of view over a greater field, often called the field of regard. These scanners may be categorized as refractive and reflective and as prismatic and pyramidal.
The pyramidal, prismatic, reflective scanners consist of the plane mirror, a two-sided mirror, a three-sided mirror, and other polygons with other numbers of sides. They are spun about an axis and generate a scan in a single direction. These are shown for four-sided geometries in Fig. A. 1. The prismatic scanner, shown on the left, is a geometric polygon that is extended perpendicularly in the third dimension. The pyramidal scanners are pyramidal, although usually the point is blunted.
The refractive scanners are both prismatic and pyramidal, but polygonal in a different way, mainly a pair of prisms.
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