| 摘要 |
PURPOSE:To reduce the size of a device and improve an image by a method wherein a screening plate partially having an open part is disposed in a light path of a laser beam, and an effective beam spot is reduced in diameter by being diffracted by the screening plate. CONSTITUTION:On a signal transmitted from an image information signal source, a laser drive circuit 1 is driven. A beam position is scanned by a laser beam scanner comprising a semiconductor laser part 2, a collimator 3, a screening plate 6, a polygon mirror 4, and an ftheta lens 5, whereby a beam spot is formed on a photosensitive drum 10. By being diffracted by the screening plate 6 provided with an open part 61 and a screening part 62, a laser beam has a laser light intensity distribution keeping side lobes on a condensing surface. By increasing the width of the screening part 62, the width of a main lobe 31 can be reduced and, simultaneously, the laser light intensities of side lobes 32, 33 can be increased. Using the photosensitive drum 10 having light quantity-electrified potential attenuation characteristics, the drum 10 is not affected by light in a small-light quantity range 40. Substantially, a beam spot diameter can be reduced. |
