Light beam optical scanning system having an f theta mirror

摘要

A laser beam optical scanning system having a laser diode, a collimator lens, a cylindrical lens, a polygonal mirror and an f theta mirror. The f theta mirror has a free toric surface whose curvature in the main scanning direction varies in accordance with field angle. The variation of the curvature of the free toric surface is set in accordance with the position of the f theta mirror in the optical path, and this appropriate setting of the variation of the curvature enables the f theta mirror to correct both distortion and curvature of field in the main scanning direction.