| 摘要 |
PURPOSE:To obtain an image forming spot with an approximately regular circle shape by making a focal position in a main scanning direction coincide with an image formation scanning face, shafting a focal position in a subscanning direction from the image formation scanning face by a prescribed distance in an optical axis direction and making the diameter of a beam approxiamtely coincide with a beam waist in the main scanning direction. CONSTITUTION:A large beam waist Wdp out of beam waists Wdp, Wds in the main scanning direction and subscanning direction is positioned on the scanning image formation face and the beam waist position in the subscanning direction, i.e. the focal position in the subscanning direction, is shifted from the scanning image formation face. Thereby, the diameter of the beam in the subscanning direction on the scanning image formation face is >= the Wds and the beam diameter Bds in the subscanning direction is increased in accordance with the increase of the shifting distance of the focal position in the subscanning direction from the scanning image formation face. Thereby, the shifting distance is adjusted so that Bds=Wdp is formed. Consequently, the image forming spot with the approximately circular shape can be obtained. |
