[Solid_cc] WLS coated MAPMT performance question

[Brad Sawatzky]

On Mon, 29 Aug 2016, Michael Paolone wrote:

> > 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.

If the wavelength shifter material is fully transparent above 300-350
then why does the material look cloudy when applied -- shouldn't it be
clear?


One other question that came to mind was whether the WLS florescence
delay messes with the timing you want for background suppression.  If
you're assuming coincidence gates of ~40ns, then it won't matter a bit.
If you're thinking of something really tight, like 10ns, then the tail
of the florescence decay time could matter.

-- Brad