Patent ID: 7554736

Claim:
An objective lens for converging a monochromatic light flux having a specific wavelength in a range of 350 to 450 nm on an optical information recording medium while the objective lens is placed facing the optical information recording medium, the objective lens comprising: a lens body containing a polymer resin having an alicyclic structure; and an antireflection film including one or more layers provided on a surface of the lens body facing to the optical information recording medium, wherein a refractive index of the antireflection film for a light flux having a wavelength of 405 nm is less than 1.7, and wherein the antireflection film comprises: a first layer containing aluminum oxide, the first layer satisfying: 45 nm≦d 1 ≦90 nm, where d 1 represents a thickness of the first layer, and a second layer containing silicon oxide, magnesium fluoride, a mixture of silicon oxide and aluminum oxide, or a mixture of silicon oxide and magnesium fluoride, the second layer satisfying: 60 nm≦d 2 ≦90 nm, where d 2 represents a thickness of the second layer.