Re: [ATM] Borofloat 33

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Stathis Kafalis wrote:

>
>>I think the 92% includes the reflection losses from the two faces.
>>
>
>Really? Can somebody confirm this or the opposite? To my understanding the 
>transmittance number should allways be given without reflection losses, but I 
>don'r know for sure. If I look through them (25 mm thickness), they seem to 
>be completely clear like looking throuh a clean window, but I can't say, if 
>this is as good as with optical glass.
>
>
You can verify it for yourself.  The plot lists (for most of the
visible wavelengths) about 92% trasmission at 0.7 mm thickness.
If this were only internal transmittance, the transmission is
proportional to the power of the thickness.  In this case, the
transmission at 5 mm would be 0.92^(5/0.7) or about 0.55.  It
isn't, so there must be something else that causes almost all
the loss (the lines for 0.7 and 5.0 mm thicknesses aren't too
far apart in that region).  That something else is the reflections.
That loss is also about what you'd expect from such a reflection,
4% is the number I've usually seen bandied about; two of those
would be pretty close to putting it at the 92% level.
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