Optical pickup apparatus and objective lens for optical pickup apparatus

摘要

In an objective lens for use in an optical pickup apparatus for converging a light beam from a laser source onto an information recording surface through a transparent substrate of an optical information recording medium, the objective lens includes: a lens surface so that a spherical aberration is discontinuous in a third numerical aperture (NA3) on a side of the optical information recording medium, and the third numerical aperture (NA3) is satisfied the following condition, $wherein\; a\; first\; numerical\; aperture\; (NA1)\; is\; a\; numerical\; aperture\; of\; the\; objective\; lens\; on\; a\; side\; of\; a\; first\; optical\; information\; recording\; medium\; having\; a\; first\; thickness\; (t1),\; required\; for\; obtaining\; an\; information\; from\; the\; information\; recording\; surface\; of\; the\; first\; optical\; information\; recording\; medium.$