| 摘要 |
PURPOSE:To prevent a variation of a scanning position caused by generation of an aberration on the scanning surface and a variation of wavelength of a semiconductor laser light source, by providing a wave surface converting element on which the same hologram as a hologram facet is formed, between a light source and a hologram disk. CONSTITUTION:The same hologram as a facet 21 is placed adjacently in front of the facet 21 as a wave surface converting element 4, and when a luminous flux of a wave surface Rc obtained by a usual lens, etc. is made incident to said hologram, a wave surface Qc is made incident to the facet 21, and when the wave surface Qc is considered to be equal to a wave surface Q, a wave surface R having no aberration is emitted. A ''0''-order diffracted light Po which has passed through the wave surface converting element 4 appears, but a projecting beam P on the scanning surface and the ''0''-order diffracted light can be separated by varying by a very small quantity one of an interval (d) of the facet 21 and the wave surface converting element 4 and its parallel degree, or an incident angle of the wave surface Rc. Therefore, Po can be eliminated easily by providing a slit 5. In this way, a drop of the scanning accuracy caused by an astigmatism and a variation of wavelength of a light source can be reduced. |
