Method of obtaining a narrow field of view scan

Abstract

Disclosed is a scanning device (10) having a very fast raster scan and a small angle field of view. The scanning device (10) incorporates a rotating polygon scanning wheel (12) in which a beam of light (24) is reflected off of a first facet (14') of the wheel (12). A reflected beam (32) from the first facet (14') is directed through an optical subsystem that reverses the scanning direction of the beam and redirects the beam onto a second facet (14') of the scanning wheel (12). Since the subsystem optics reverses the scan of the beam, the second facet (14') scans the beam in an opposite direction to that of the first facet (14') and only the difference between the two scans remains. In a first embodiment, the optical subsystem magnifies or demagnifies the beam such that the angle of scan is enlarged or reduced, and thus the second scan will not completely cancel the first scan. Consequently, a very narrow field of view of a particular scene can be scanned very quickly. In an alternate embodiment, the size of the scan is altered by either altering the convergence or divergence of the beam between the two scanning reflections to achieve the small angle scan. In yet another embodiment, the small angle scan is achieved by substantially, but not entirely, reversing the scan direction.