[Solid_cc] WLS coated MAPMT performance question

[Sylvester J. Joosten]

Hi Zhiwen, Hi Michael,

I have a few additional comments:

1. The WLS spectra you are showing come from a preliminary test where the coating thickness wasn’t fully saturated. We have since then perfected the coating application on the MAPMTs. You can find a figure of a more recent test, comparing the measured QE with coating at 5 different wavelengths, with a theoretical calculation. It would suggest to use the theoretical curve for your simulation.

2. See Michael’s answer. Bottom line is that the WLS is fully transparent above ~300nm.

3. We are the only group besides CERN capable of doing vacuum deposition of p-Terphenyl, which is necessary to get a sufficient thickness of p-Terphenyl without crystallization ruining the layer. Our measured results for the CLAS LTCC are better than better than what has previously been published. We are currently finishing a publication to be submitted to NIM detailing our procedure and findings.

Le me know if you have any additional questions!

Cheers,
Sylvester 


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> On Aug 29, 2016, at 10:11 AM, Michael Paolone <mpaolone at jlab.org> wrote:
> 
> Questions are answered below:
> 
>> Hi, All
>> If you are receiving this, it means I added you into the
>> solid_cc at jlab.org list.
>> It can be used to discuss shared topic between LGC and HGC
>> (I also setup a separated list solid_hgc at jlab.org for HGC only)
>> 
>> 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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