| 摘要 |
A diffractive lens has a plurality of diffractive zones at least one of which has an optical step having an optical height equal to j .lambda. and at least one of which has an optical step having an optical height equal to k .lambda. where .lambda. is a design wavelength of the lens and j and k are unequal nonzero integers. Alternatively stated at least one of the optical steps induces a relative phase shift of 2j.pi. at the back conjugate point between two light rays emerging from a point source at the front conjugate point and striking the lens immediately on opposite sides of the step and at least one of the steps induces a relative phase shift of 2k.pi. at the back conjugate point between two light rays emerging from a point source at the front conjugate point and striking the lens immediately on opposite sides of that step.
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