Objective lens, an optical pickup, and optical information recording/reproducing apparatus

An optical pickup, comprising

• a light source that emits a light beam at a wavelength λ of 450 nm or less, and
• an objective lens having a numerical aperture of 0.8 or more and focusing said light beam on an optical information recording medium, wherein
• said objective lens shows a wavefront-aberration deterioration level TOR, a cumulative value of aberration deterioration, satisfying the following equation (7):
• TOR=√{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}≦0.07[λrms] (7)
• wherein
• TSA3 [λrms/μm] refers to a third-order thickness sensitivity level, which is a third-order spherical aberration level generated when a thickness error from a predetermined thickness is +1 μm,
• TSA5 [λrms/μm] refers to a fifth-order thickness sensitivity level, which is a fifth-order spherical aberration level generated when a thickness error from a predetermined thickness is +1 μm,
• DCm3 refers to a third-order decentering sensitivity level, which is a third-order coma aberration level generated when a decentering error of each of lens surfaces is 1 μm, and
• DCm5 refers to a fifth-order decentering sensitivity level, which is a fifth-order coma aberration level generated when a decentering error of each of lens surfaces is 1 μm.

An optical information recording/reproduction apparatus, comprising:

• a light source that emits a light beam at a wavelength λ of 450 nm or less;
• an objective lens having a numerical aperture of 0.8 or more and focusing said light beam on an optical information recording medium;
• and
• a position control unit that controls the position of said objective lens so that the focus of said objective lens is placed on a desired point on said optical recording medium, wherein
• said objective lens shows a wavefront-aberration deterioration level TOR, a cumulative value of aberration deterioration, satisfying the following equation (8):
• TOR=√{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}≦0.007[λrms] (8)
• wherein:
• TSA3 [λrms/μm] refers to a third-order thickness sensitivity level, which is a third-order spherical aberration level generated when a thickness error from a predetermined thickness is +1 μm,
• TSA5 [λrms/μm] refers to a fifth-order thickness sensitivity level, which is a fifth-order spherical aberration level generated when a thickness error from a predetermined thickness is +1 μm,
• DCm3 refers to a third-order decentering sensitivity level, which is a third-order coma aberration level generated when a decentering error of each of lens surfaces is 1 μm, and
• DCm5 refers to a fifth-order decentering sensitivity level, which is a fifth-order coma aberration level generated when a decentering error of each of lens surfaces is 1 μm.