A novel laser beam deflector that utilizes rotating holographic gratings in a pyramidal geometry is described. Total rotational symmetry with regard to imaging properties is achieved with this deflector geometry, and therefore, it can be used for either flat-field or internal drum scanning applications. The scan beam from this deflector is bow free and totally uneffected by deflector wobble and centration errors.
Charles J. Kramer,
"Hologon Deflector For High-Resolution Internal Drum And Flat-Field Imaging", Proc. SPIE 1079, Hard Copy Output, (6 July 1989); doi: 10.1117/12.952829; https://doi.org/10.1117/12.952829