Dispersion of Selfoc lens originates from the wavelength dependence of the refractive index on axis
N0 and a constant
A, where refractive index distribution is expressed as
N=
N0 (1-
A/2
r2).
So far
N0 and
A can not have been measured separately. Here, we proposed a new method of measuring
A and
N0 separately.
First,
A can be determined by making the parallel incident beam focus on the output end surface of Selfoc lens whose length is set up to a quarter of its periodic length.
Namely the length of Selfoc lens (
Z0) is measured under this condition, and
A can be derived from the relation
A= (π/2
Z0)
2.
Secondly, we measured a distance (
S) between the spot and the output end surface of Selfoc lens whose length (
Z) is set up to shorter than a quarter of the periodic length. We found, then
N0 from
N0=1/
S√
A tan √
AZ.
We measured
A and
N0 for various wavelengths, and derived dispersion of
A and
N0 separately.
We found the relation between
A and λ (wavelength) such as,
A= (
A2+
B2/λ
2) / (
A1+
B1/λ
2)
R2, where
R is the radius of the Selfoc lens.
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