[size=+3]Wide Infrared Bandpass Filter
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This coating is for light at normal incidence on a germanium substrate (index 4). The requirements are:, W7 f/ [- \, o _, q4 d' B
A. Transmittance 99% for wavelengths 3300-5000 nm
& }7 p/ k, w0 B, w! ^$ R7 f, h% N$ A% wC. Transmittance Second, starting with a single thin layer, the needle/tunneling method was used to create a 17-layer short-wave pass filter using requirements B and C. The performance is shown below.
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Third, experience shows that it is best to place the short-wave pass filter closest to the substrate and then to append the long-wave pass filter. (The needle/tunneling method "discovers" this fact when the brute-force approach is used.) Before optimizing, the performance is: , Q. u. E1 |7 T# e4 c
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After optimizing this design, the final performance is:
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Here are the designs, with the first layer closest to the substrate and thickness given in nm. With a little more work, it may be possible to eliminated some thin layers. 1 m7 n+ h0 ]1 @" [) ~: Q! I
Short Long Bandpass5 e* K0 U$ o! _
ZnS 83.39 97.33
& H2 {6 G) \( n# h. D' T Ge 48.25 48.60
) h% q& a3 u- ~5 M) M: \ ZnS 756.31 761.473 e# b0 z6 @, ~
Ge 403.51 412.85
8 r+ w& N! w" H2 M4 o9 O5 w0 O ZnS 710.33 720.06! }, q+ {1 T' t) D6 V* E% p; g, {
Ge 377.93 382.28
- i3 i; y; j* ~( P# c; E3 u3 ~ ZnS 696.05 705.03
* Y0 ~& V$ k% Q3 a$ T Ge 370.17 370.423 ]3 }7 K8 |1 r7 _$ E
ZnS 696.91 709.26
# S, y$ d$ C' @2 s' @: Q& D# U Ge 365.05 358.23" r( Z3 n: Z9 A. x' |+ {8 k( _8 j
ZnS 705.00 718.52
6 z& `4 P: a$ v Ge 361.44 353.080 q# {, H) U* @ y
ZnS 719.03 724.86' u0 S5 H( n3 v) p! S3 r8 B
Ge 360.53 360.01
# k0 Y) m6 l9 n2 [) G% J! Y0 H" r ZnS 751.56 710.47
# U0 x) M- g7 ?) W# J4 H Ge 328.61 398.52- c! T$ F! t$ u/ t F8 _9 R! \
ZnS 369.01 158.71 564.95
+ \, Q, ?6 C" l' l5 @; o/ k" N Ge 124.38 40.790 l# j2 {" s- w8 |
ZnS 260.14 224.72
! _" X; |, `2 G, E; _ Ge 78.55 125.31
' N6 v6 R6 R& b: L% O ZnS 149.33 133.58- A# y7 X/ M- s8 }
Ge 102.25 98.28
2 U" ]4 v0 T' I+ o% ^ ZnS 235.97 268.21
: x% ~" j V% j Ge 145.53 138.253 b( q' ~9 Y! R6 R4 d. m
ZnS 279.07 238.01
4 [6 R- J$ f$ p/ w) v ]7 u7 o Ge 128.80 125.48# I |; |. C) s: x' z
ZnS 196.52 232.65
- x0 g6 ~) w) y Ge 67.11 68.54 ~& V, a3 M$ t9 [
ZnS 159.26 168.55
! `- [9 c; l- @6 ?9 _ Ge 132.16 150.14, Z" ~2 { _; Q
ZnS 271.50 254.28
5 B( K4 m9 y# @) T5 q: ? Ge 144.32 125.25
, X+ M0 H J* o4 h" O ZnS 281.93 307.19
- j& l! Y8 S: J+ }7 ` Ge 149.33 165.16
8 N! P" o! l5 d; q ZnS 278.65 256.22- Y) P& t% I0 S3 m9 K
Ge 140.79 133.04
. M. _, Y5 \6 X. R ZnS 271.93 289.60' ` J" M f* ~; o
Ge 147.16 147.63" ]% G0 r0 u* \$ { ^: z
ZnS 276.89 266.04% S) i5 x m) J# p
Ge 138.39 134.34- {! @" [2 v- v" o7 {. i
ZnS 271.52 265.60
- d+ r" n1 `% l* h: v& o1 \. D Ge 152.12 156.86
" g+ A8 F# h* A+ j z ZnS 291.92 294.156 s1 x& g, g! V
Ge 135.69 123.17- j" l1 D }/ x' T1 o2 X0 k
ZnS 249.93 250.12
+ M1 b$ A B. ]6 d! M Ge 166.98 178.96
! {6 o3 G2 d5 `3 ?" _ ZnS 553.73 528.64 |