Patent ID: 6977781

Claim:
A scanning optical system for dynamically deflecting a laser beam emitted from a light source by a deflecting system, converging the dynamically deflected laser beam by an imaging optical system into a spot beam on a scan target surface, and thereby scanning the spot beam in a main scanning direction on said scan target surface, comprising: an optical element being placed on an optical path between said light source and said deflecting system, said optical element including: a central area transmitting part of the laser beam in the vicinity of a central axis of the laser beam; at least one first outer area transmitting part of the laser beam incident on part of said optical element outside said central area while having an effect on the laser beam so that the beam after passing through said at least one first outer area will be in a first phase state which does not include a state where the beam has no phase difference relative to a beam passing through said central area; and at least one second outer area transmitting part of the laser beam incident on part of said optical element other than said central area and said at least one first outer area while having an effect on the laser beam so that the beam after passing through said at least one second outer area will be in a second phase state which is different from said first phase state and includes a state where the beam has no phase difference relative to the beam passing through said central area.