Chemistry Reference
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n
~ 1.69) is coated prior to the coating of low-index layer (MgF
,
H
2
n
. The
necessary and sufficient index condition for zero reflectance is (
~ 1.38) onto a glass substrate (
n
~ 1.5), while
n
>
n
>
n
L
s
H
s
L
n
/
L
2
n
. Even though this approach leads to a phenomenal drop
of the effective reflectance
)
=
n
/
n
M
s
0
R
at a particular target wavelength
eff
(
l
), but simultaneously increases the
R
on both sides of
l
t
eff
t
[Fig. 2.3a(ii)], even higher than that of single-layer ARC [Fig. 2.3a(i)].
Figure 2.3
(a) Layer-structured ARCs: Reflectance (
R
) as a function
l
of wavelength: (i) Single-layer: air (
n
= 1.0)/0.25
-MgF
0
t
2
(
n
= 1.38)/glass (
n
s
= 1.52); (ii) Double-layer: air/0.25
l
-
t
MgF
/0.25
l
-Al
O
(
n
= 1.69)/glass; (iii) Three-layer:
2
t
2
3
H
air/0.25
=
1.64)/glass. Reprinted from Ref. [1], Copyright 2010, with
permission from Elsevier. (b) Gradient-RI ARCs: semi-bounded
linear, concave-parabolic, convex-parabolic, and cubic GRIN
profiles, all of which show an index discontinuity from 1
to 1.1 at the free surface (z = 0), but no discontinuity at the
layer-substrate interface, where
l
-MgF
/0.5
l
-ZrO
(
n
= 2.05)/0.25
l
-CeF
(
n
t
2
t
2
M
t
3
H
= 1.5. Reprinted from Ref.
[16], with permission from The Optical Society, Copyright
1982. (c) Linear-, cubic- and quintic-index profiles that have
index matching with air and a substrate with
n
= 2.05; and
their respective reflectivities with (d) wavelength-dependence
(at normal incidence) and (e) AOI-dependence at
n
s
l
= 632.8
nm. Reprinted by permission from Macmillan Publishers Ltd.:
Nature Photonics
t
, Ref. [17], Copyright 2007.
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