Diffractive optical element and optical pickup apparatus

摘要

The present invention relates to a diffractive optical element which has chromatic aberration capable of recording and reproducing without any problem even in the case of instantaneous wavelength change in a laser beam that cannot be followed by an actuator, and can control an adverse effect caused on a spot diameter of a converged spot and on a signal read by a sensor. The diffractive optical element includes a diffractive structure, and diffraction efficiency of m^th order diffracted beam satisfies prescribed conditions, and a distance between a paraxial converging position of the diffracted beam having a higher diffraction efficiency among (m+1)^th order diffracted beam and (m-1)^th order diffracted beam and a paraxial converging position of the m^th diffracted beam satisfies prescribed conditions, when m represents a diffraction order number of the diffracted beam used for the first optical information recording medium.