POLYGON MIRROR EVALUATING DEVICE

摘要

PURPOSE: To measure eccentricity in the optical axis direction along with the measurement of lateral deviation eccentricity and an angle error relative to the optical axis of a reflection face by mounting a polygon mirror having a plurality of optical reflection faces at an equal division angle and providing a distance measurement means for measuring distance to the reflection faces of the polygon mirror. CONSTITUTION: Light of a pointlike beam 11 transmitted through a collimator lens 3 is converted into a light wave front according to the shape of a reflection plate 9a by a wave front controller 10 to be made incident on the plate 9a, and the position of the image of a target 12 by reflected light is detected and stored by an image position detector 13. Distance to the reflection plate 9a is measured by a triangulation type optical displacement gage 14 exactly opposite to the reflection plate 9a. A highly accurate rotation stage 2 mounting a polygon mirror is rotated in the direction A by 90 deg. so as to face the reflection face 9b to a lens 3, and deviation of the image of the target 12 which is reflected by the reflection face 9b is measured by the device 13. Positions of the images of the reflection faces 9a and 9b are compared so as to understand lateral deviation eccentricity. Distance to the reflection face 9b which is measured by the displacement gage 14 is compared with that to the reflection face 9a so that eccentricity in the optical axis direction is found.