[Solid_cc] WLS coated MAPMT performance question

[Michael Paolone]

Questions are answered below:

> Hi, All
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> Michael
> We had some discussion about the measured QE curve from H12700_03 coated
> with WLS and have some questions
> In the attached plot, the green lines shows the QE curve you gave me.
> 1. why there is up and down wave like change between 250-300nm

The absorption/remittence spectrum isn't flat.  See attached file.

> 2. above 350nm, it shows no change comparing to uncoated PMT. If the
> main feature of WLS is shifting light to UV, why QE won't drop at high
> wavelength?

It works the other way, Higher energy (low wavelength) photons are
absorbed and reemitted as lower energy (high wavelength) photons.  So why
isn't there a bump at higher wavelengths, you might ask?  The QE spectra
has the WLS effects folded in.  So a photon at 250nm on the QE plot has an
average effective QE of the 250nm photons that were not absorbed averaged
with the QE of the reemitted photons at higher wavelengths.  On the QE
plot, photons at 350nm are not absorbed at all, so their effective QE is
not changed.

> 3. Donal's group at UVa did similar coating, have you had any crosscheck
> with them or their result.

Not that I know of.  I can check with Sylvester and Zein-Eddine.

>
> Thanks
>
> Zhiwen
>
>
>
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