| 摘要 |
An aperture has an aperture opening that transmits a predetermined portion of a light beam. A phase optical element changes a phase of a portion of a light beam. A scanning lens focuses the light beam into a beam spot on a scanning surface. The phase optical element has a function of increasing light intensity of a side-lobe of the scanning beam near the scanning surface. The aperture opening is set to satisfy 0.03<=(SR-SA)/SR<=0.20, where SR and SA are areas of a rectangle circumscribing the aperture opening and the aperture opening, respectively. The function of the phase optical element and the aperture expand a depth allowance of the beam spot.
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