[Solid_cc] WLS coated MAPMT performance question

[Garth Huber]

Thank you Sylvester and Michael for the information.

It is great news that you have been so successful with vacuum deposition.  My 
understanding is that this results in a significant improvement of WLS coating 
compared to other methods.

As Brad mentioned, a copy of a technical report when you have one available 
would be very welcome.

Do you expect to eventually have QE measurements below 240 nm?

Garth Huber

Sylvester J. Joosten wrote:
> 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
>
>
>
>
>
>> 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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-- 
Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada.
tel: 1-306-585-4240. fax: 1-306-585-5659.