Objective lens, optical head, optical disk device, and information processing device

An objective lens made from synthetic resin, that converges a laser beam emitted from a laser light source onto an information recording surface of an information recording medium, the objective lens comprising:

• a lens having a first surface facing the laser light source and a second surface facing the information recording medium;
• and
• an anti-reflection coat formed on the second surface, wherein
• the lens converges a first laser beam having a first wavelength λ1 (390 nm≦λ1≦430 nm) that transmits through an area, of which radius from an optical axis of the objective lens is R1, of the first surface, onto an information recording surface of a first information recording medium, and converges a second laser beam having a second wavelength λ2 (630 nm≦λ2≦680 nm) that transmits through an area, of which radius from the optical axis of the objective lens is R2 (R2<R1), of the first surface, onto an information recording surface of a second information recording medium that is different from the first information recording medium,
• a transmittance T1_0 [%] of the anti-reflection coat when an incident angle of the first laser beam is 0° and a transmittance T1_40 [%] of the anti-reflection coat when the incident angle of the first laser beam is 40° satisfy 0.95≦T1_0/T1_40≦1.05,
• in the area of which radius is R2, a transmittance of the first laser beam satisfies the transmittance ≧92%,
• a transmittance T2_0 [%] of the anti-reflection coat when an incident angle of the second laser beam is 0° satisfies 85%≦T2_0<96%, and
• a transmittance T2_40 [%] of the anti-reflection coat when the incident angle of the second laser beam is 40° satisfies T2_40≧94%, and
• the transmittance T2_0 and the transmittance T2_40 satisfy 0.85≦T2_0/T2_40≦0.97.