Re: [ATM] What is the "dielectric" in dielectric coatings?

["Vladimir Galogaza" <vladimir.galogaza@zg.htnet.hr>]

Ken,

But on a second thought.

If reflectivity of metal is (arbitrary) 90% meaning that
without coating 90% of input intensity will be reflected, 10% absorbed.

If there is coating with reflectivity 4% 

4% of input intensity will be reflected by coating (arbitrary).
96% will enter coating and fall on the metal
90% of this 96%   will be reflected by metal this amounts to 86.4% of 
        input intensity on  the coating
if in phase this 86.4% will be added to 4% which is total 90.4%.

Assumptions
1) There is no additional reflection on the coating-metal boundary 
of incoming light 
2) same  on the coating-air boundary of the outgoing light.
3) coating has zero absorption (100% transparent).

 0.4% enhancement in reflectivity comes from less light entering metal and
absorbed there .

Multi level coating can increase this gain by reflecting more light 
before it reaches metal.
Actually it is possible to avoid metal completely (dielectric mirror), 
but the price will be narrower spectral band and greater
dependency on input angle due to interference condition.

Does this sounds reasonable to the public on the list?

Regards
Vladimir.



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