Optical element, lens and optical head device

摘要

An optical element includes a diffraction grating by which both a first laser beam and a second laser beam are diffracted. A diffraction performance of the diffraction grating is expressed by an optical path difference function, a third spherical aberration SA31 of the first laser beam and a third spherical aberration SA32 of the second laser beam in a wave front aberration calculated by the optical path difference function satisfy the following conditional expressions: 0.005<|SA31-SA32|<0.015 [lambdarms] SA31xSA32<0.