| 摘要 |
An objective lens to converge a light flux having a working reference wavelength lambda<SUB>0 </SUB>(380 nm<=lambda<SUB>0</SUB><=450 nm) under a working reference temperature T<SUB>0 </SUB>onto an optical information recording medium equipped with a protective substrate having a thickness of 0.6 mm with almost no aberration. The diffractive structural section of the objective lens has a first compensating function to compensate a change amount deltaSA 1 of the third-order spherical aberration component of wavefront aberration caused by a fluctuation of a working wavelength, a second compensating function to compensate a deviation deltaWD of a converged-light spot in an optical axis direction caused by a fluctuation of a working wavelength, and a third compensating function to compensate a change amount deltaSA 2 of the third-order spherical aberration component of wavefront aberration caused by a change of a refractive index of the lens body.
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