| 摘要 |
PURPOSE:To reduce beam power loss due to lens insertion and to facilitate an adjustment of an optical system by making focal surfaces of optical convergence systems which are arranged on a beam incidence and a projection side coincident, and arranging a modulating element on an optical path off the focal surface. CONSTITUTION:When a mirror surface 41 and a rotating shaft 40 has an angle alpha of inclination owing to work precision, light incident to a polygon mirror 4 forms an image on a drum 6' with a shift of an angle 2alpha to cause scanning pitch unevenness, so the light is made incident to the surface 41 at the angle 2alpha of inclination. For this purpose, a diffraction angle C is determined by varying the carrier frequency of an acoustooptic modulating element AOM2' according to the slanting angle alpha from C=2alphaXf2'divided by l1' where C and D are angle of inclination of a light beam diffracted by the AOM2' and a light beam incident to a mirror surface 41' of the polygon 4, f2' and l1' are the focal length of a lens L2' and the distance from the AOM2' to the focal surface, and the angle D of inclination is 2alpha. Therefore, the number of lenses decreases, so the beam power loss is reduced and the adjustment of the optical system is facilitated. |
