Light beam scanning apparatus

摘要

A light beam is made to impinge upon a plane diffraction grating formed on a rotatable plate so that the plane of incidence is a plane in which the rotation axis of the rotatable plate lies. The light beam diffracted by the diffraction grating is reflected and guided again to the diffraction grating by use of a cylindrical lens the axis of which is normal to the plane of incidence and a plane reflection mirror normal to the plane of incidence, or by use of a combination of two relay lenses having equal focal lengths with two plane reflection mirrors. The light beam diffracted again by the diffraction grating is focusing by a focusing lens onto a scanning surface, so that the scanning surface is scanned with the focused light spot along a bow-free straight scan line as the rotatable plate is rotated.