| 摘要 |
PURPOSE: To provide an objective lens which has a numerical aperture as large as >= 0.5, maintains the state well corrected of spherical aberrations even under an environmental change, such as a temperature change and does not make the downsizing of an optical pickup device difficult. CONSTITUTION: The objective lens is formed of a single lens of a finite system and the first surface and second surface thereof are formed as aspherical surfaces. A hologram is formed on at least one of these aspherical surfaces. The plus first order light or minus first order light of the hologram is subjected to an optimum spherical aberration correction in an actual use state. In the case a semiconductor laser is used as a light source, the change in the spherical aberrations of the hologram by the change in the oscillation wavelength of the semiconductor laser arising with a change in the environmental temperature nearly offsets the change in the spherical aberrations caused by the change in the refractive index by accompanying the change in the environmental temperature of the medium between the first surface and the second surface.
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