| http://www.w3.org/ns/prov#value | - The optical pickup of claim 11, wherein when the phase difference according to a wavelength variation of the first light beam from the wavelength ??0 to a wavelength ??1 is expressed as ((n1a???n1b)???z(h)), wherein n1a and n1b are the refractive indices of the first and the second retardation members for the wavelength ??1, and h is a distance from the optical axis, and z(h) is, respectively a he
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