Patent ID: 7471611

Claim:
A zone phase correcting lens, comprising: a plurality of zone refractive surfaces adjacent to each other via an adjacent step in the optical axis direction on at least one of the first surface and the second surface; said zone phase correcting lens being formed so as to correct a phase for each of the zone refractive surfaces; wherein, supposing that: λ 1 is the wavelength of a first laser beam incident on the zone phase correcting lens and λ 2 is the wavelength of a second laser beam having a longer wavelength than the first laser beam; a minus sign is appended to a height measurement of an adjacent step formed so as to make an outer zone refractive surface thinner in lens thickness in the optical axis direction than an inner zone refractive surface and a plus sign is appended to the height measurement of an adjacent step formed so as to make the outer zone refractive surface thicker in lens thickness in the optical axis direction than the inner zone refractive surface; D is an absolute value of the sum of the height measurements of the adjacent steps having the minus sign formed on the first surface, the second surface, or the both surfaces; and E is an absolute value of the sum of the height measurements of the adjacent steps having the plus sign formed on the first surface, the second surface, or the both surfaces; then, the wavelength λ 1 , the sum D, the sum E, and a refractive index N 1 of the zone phase correcting lens for the first laser beam satisfy the following relationships: 10×λ 1 <{D ×( N 1 −1)}<30×λ 1 2 ×E<D.