Cold Mirror

[size=+3]Cold Mirror
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A cold mirror reflects short wavelengths and transmits long wavelengths. The are many applications for this type of coating. In this example, we require that the coating consist of layers of SiO2 and TiO2 on a glass substrate and have the following performance at normal incidence:
& c) |( Y1 ]/ I/ J" U( c> 90% reflectance for 380-750 nm
* S$ @1 m2 A) @3 w9 LThe prime difficulty with this type of coating is the design of the reflector. After an acceptable reflector has been designed, it is usually easy to extend the transmitting region. For instance, the plot below shows the 21-layer design extended to 2000 nm.

Here are the designs, starting with the layer closest to the substrate, and with thicknesses given in nm:
4 `+ y- s) H* p; n4 P4 ?5 E5 Q& ~/ vTIO2      44.21     33.76
SIO2     102.57    124.04
9 x1 X; u6 o* i5 G$ ETIO2      43.97     28.39
6 k/ ^! f2 Y. DSIO2      73.13     66.36
  U8 A3 j. |: H  u" F4 wTIO2      42.56     51.05
! k/ s% p5 y* o7 _" S+ v9 {SIO2      82.52     86.41
% K, U# N3 y% C# ]: i/ VTIO2      48.92     51.97
, b5 Z. ]9 D8 kSIO2      87.18     88.77
$ y' W+ H" a: r6 kTIO2      46.48     39.55
2 y& f, z3 {! a9 pSIO2      66.56     70.41
$ S3 Y6 Y& R. H/ ]9 O* XTIO2      36.16     36.85
7 {' _# ^# c1 z$ A% WSIO2     162.54    162.37
TIO2      53.07     53.15
0 W+ H7 @, u) @7 @. ASIO2      97.19    102.08
6 G, x4 J$ u; W' X$ h( F6 WTIO2      79.13     81.48
- |, @. J9 Z# p9 b' E" ^SIO2     102.19     99.64
( E) P# A( C8 r! `0 TTIO2      67.77     61.86
SIO2     128.87    137.38
TIO2      53.24     51.30
SIO2     158.61    191.13
TIO2      34.40     19.03