Patent attributes
A phase shift element has a tiered phase difference pattern portion, in which an inner circular side tiered phase difference pattern portion is continuously connected with an outer circular side tiered phase difference pattern portion based on a phase function curve obtained by a single phase-function with a wavelength having the same value as a reference wavelength λ1 of a first laser light being determined as a designed wavelength λ, formed in annular shapes on one surface thereof. A tier pitch of tiers of the inner circular side tiered phase difference pattern portion is set to a height corresponding to a phase difference of substantially 1λ and, on the other hand, a tier pitch of tiers of the outer circular side tiered phase difference pattern portion is set to a height corresponding to a phase difference of substantially mλ (where m is a natural number which does not include 0) or a height corresponding to the phase difference of substantially mλ by changing a value of m for each step.
