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:
> 90% reflectance for 380-750 nm
8 \4 b2 f6 R) N7 BThe 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.
0 B3 H$ {, E% L7 L
Here are the designs, starting with the layer closest to the substrate, and with thicknesses given in nm:
9 f8 p3 A# a9 R8 J& yTIO2      44.21     33.76
SIO2     102.57    124.04
TIO2      43.97     28.39
# s' u3 Y+ ?& w) WSIO2      73.13     66.36
TIO2      42.56     51.05
SIO2      82.52     86.41
7 s1 o; I7 m, a7 ]2 tTIO2      48.92     51.97
2 N5 }8 e7 U0 H: k; [& N" ASIO2      87.18     88.77
- q; k2 _8 Z5 uTIO2      46.48     39.55
SIO2      66.56     70.41
TIO2      36.16     36.85
$ d) f; G9 h  d8 G* KSIO2     162.54    162.37
TIO2      53.07     53.15
* P; ?. Y/ {' w% Q  i9 hSIO2      97.19    102.08
TIO2      79.13     81.48
( }- ^9 L# u; MSIO2     102.19     99.64
TIO2      67.77     61.86
, `3 c; ^$ \8 f9 K/ h# k$ PSIO2     128.87    137.38
TIO2      53.24     51.30
SIO2     158.61    191.13
0 t) L1 D9 M4 t* zTIO2      34.40     19.03