| 摘要 |
PURPOSE:To make it possible to measure the slant angle of the plane of a rotating polygon mirror at every mirror plane relatively and highly accurately, by comparing the interference fringes formed by the reflected light by each mirror plane and the reflected light from the surface of a transmitting member. CONSTITUTION:At the stationary state of a polygon mirror, interference fringes 9 are generated by a specified mirror plane 5b, which is a reference plane. Then the polygon mirror 5 is rotated. When the specified number of rotation is reached, the ON and OFF synchronization of a laser beam 2 is controlled by a light source 1, so that only reflected light 7 from the reference mirror plane 5b and reference light 8 from the surface are projected on a projection plane 10. The timing of said synchronization control is slightly adjusted finely by the same means. Then interference fringes 9' corresponding to all the mirror planes other than the reference plane are measured. Then the difference DELTAtheta in slant angle of each mirror plane with respect to a rotary shaft 5a can be expressed by a formula DELTAtheta (l1-l0)lambda/2l0l1, where l0 is a pitch of the interference fringes 9 and l1 is a pitch of the interference fringes 9'. Thus the slant angles of all the mirror planes with respect to the reference mirror plane can be computed accurately. |
