Light beam scanning apparatus employing rotating polygon mirror

摘要

A light beam scanning apparatus wherein a light beam deflected by a rotating polygon mirror is scanned on a scanning surface in a main scanning direction, and the scanning surface is moved with respect to the light beam in a sub-scanning direction, comprises a reference beam emitting system for generating a reference beam of a predetermined intensity and making for the reference beam impinge upon the rotating polygon mirror. The apparatus also comprises a photodetector for measuring the intensity of the reference beam deflected by the rotating polygon mirror, and a control circuit for receiving the output of the photodetector and adjusting the intensity of the light beam in accordance with the level of the intensity of the reference beam which is represented by the output of the photodetector.