PHASE SHIFTING PLATE AND OPTICAL SYSTEM PROVIDED WITH PHASE SHIFTING PLATE

摘要

Provided is an optical element which reduces the spot diameter of a laser beam while ensuring a prescribed focal depth, reduces coma aberration and is easily used in practical optical systems. A phase shifting plate is to be used for substantially parallel laser beams, and is configured to apply a phase difference of π to at least a part of the periphery of a region where the laser beams pass through.