Dear Coating guys,

I have a query. If precision polished flat is coated with edge
filter which transmits 633nm, what will happen to the form error or
power on the coated surface of the flat? To be more precise, I wish to
know whether the power increases or decreases and why?

in article 78d30f36.0311060322.7ff524c7@posting.google.com, sankar at
sandivp@hotmail.com wrote on 11/6/03 3:22 AM:

Dear Coating guys,

I have a query. If precision polished flat is coated with edge
filter which transmits 633nm, what will happen to the form error or
power on the coated surface of the flat? To be more precise, I wish to
know whether the power increases or decreases and why?

Ussually, a coating placed upon a hot substrate, will shrink faster than the
substrate upon cooling. This puts the coating in tension. On a thin
substrate, it is very likely that the coating surface will become concave.

As for details, you are on your own.

Bill

Thank you very much for your info.
I have one more query. For coated precision polished flat, since
coating changes the form error, is it required to choose a convex
polished surface to compensate for concave surface after coating or
form error measurement after coating is not relevant?

in article 78d30f36.0311072148.2de1e88b@posting.google.com, sankar at
sandivp@hotmail.com wrote on 11/7/03 9:48 PM:

Thank you very much for your info.
I have one more query. For coated precision polished flat, since
coating changes the form error, is it required to choose a convex
polished surface to compensate for concave surface after coating or
form error measurement after coating is not relevant?

I think that you will find coatings on highly precise flats such as used in
Fabry-Perot interferometr mirros with rms variations in the neighborhood of
lambda/100 or so use SOFT coating materials that cannot support stress. For
that reason, the coatings are easily damaged.

Bill