| 摘要 |
PURPOSE:To prevent an optical interference and to obtain a distinct picture by providing a slantingly the surface of a parallel plate through which a laser beam for scanning a photosensitive body transmits, on a beam optical path. CONSTITUTION:A laser beam L from a rotary polyhedral mirror is irradiated to a photosensitive body 1 through a color correcting filter 16 and a glass plate 15. A beam Li which is made incident at an incident angle theta to a parallel plate 15 goes straight on and becomes a beam Li1, and also it is reflected by the inside surface of the lower side of the plate 15 and becomes a beam Li2. When a distance of two beams, the plate thickness and the refractive index are denoted as DELTAS, (t) and (n), respectively, DELTAS=2ttheta/n is formed, and when a magnitude phi of a beam of a focal plane 1 is phi<DELTAS, no optical interference occurs, therefore, if the incident angle theta is larger than nphi/2t, no interference occurs. Accordingly, by inclining transparent plates 15 (16) in a beam optical path, an optical interference is prevented and a distinct picture is obtained.
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