| 摘要 |
An objective lens element having improved diffraction efficiency at at least one of used wavelengths is provided. The objective lens element includes one surface including: a first region including an optical axis; and a second region surrounding the first region. A periodic first diffraction structure is formed on the first region, and a periodic second diffraction structure different from the first diffraction structure is formed on the second region. The objective lens element satisfies the following conditions. |A1−B1|<|A2−B2|  (1) |B1|≧|B2|  (2) Here, A1 and B1 are diffraction orders at the first region to converge light of a first wavelength and light of a second wavelength on a recording surface, respectively, and A2 and B2 are diffraction orders at the second region to converge the light of the first wavelength and the light of the second wavelength on a recording surface, respectively. |
