| 摘要 |
PURPOSE:To form a semiconductor laser beam having no isotropic extension angle in the form of an isotropic spot with high using efficiency of light, by making the beam of a non-isotropic form given from a semiconductor laser element incident on a cemented lens by increasing the numerical aperture of this lens and setting a prism at the next stage of said lens. CONSTITUTION:The change of the focus position of a reflected return light spot owing to the displacement of a disk is reduced by increasing the numerical aperture NA of a cemented lens 2 (up to 0.5). Thus the lead-in range is increased for automatic focusing. However the light beam transmitted through the lens 2 is not isotropic and therefore a light spot 5 is not isotropic either. Here a prim 7 is set at the next stage of the lens 2 in order to expand the horizontal extension of the beam given from a semiconductor laser element. Thus the coincidence is obtained between the horizontal extension and the vertical extension of the beam. Then this beam is converted into an isotropic one. |
