[Solid_cc] WLS coated MAPMT performance question

[Zhiwen Zhao]

Hi, Sylvester

Thanks for sharing the useful info.
Assuming a right lamp, what wavelength can we get with N2 gas instead of 
vacuum?

Zhiwen

On 9/2/2016 10:45 PM, Sylvester J. Joosten wrote:
> Hi Everyone,
>
> The lowest wavelength from the monochromator testing on the figure I sent you is 220nm (gain: 4.26+/-0.14). I measured one lower wavelength: 215nm (gain: 5.42+/-.28). I did not find any evidence of the gain starting to taper off.
>
> We tried to go down to 200nm with the monochromator, but both the light intensity from the lamp, as well as the absorption in the air resulted in too low count rates compared to the dark current rate at shorter wavelengths. For a reliable measurement at wavelengths below 215nm we really need to work in a vacuum. I agree it would be interesting to see a coated PMT work down to 150 nm - below what even a quartz PMT can do!
>
> I will send around a copy of the technical report as soon as we have our final draft available.
>
> Cheers,
> Sylvester
>
>> On Sep 2, 2016, at 4:49 PM, Zhiwen Zhao <zwzhao at jlab.org> wrote:
>>
>> Hi, Michael and Sylvester
>>
>> I also think testing below 240nm and down to 200nm would be very useful
>> Photon number increase quickly toward UV. Photons from that region can take a big portion out of total.
>> Knowing them reliably would be great.
>>
>> Beyond that, I think it's also very interesting to test even lower, like down to 150nm.
>> This deep UV region has a lot more of photons.
>> To harvest them , we would need PMT,mirror,gas all work together at the same time.
>> SBU is trying to make mirror down to this region for EIC R&D.
>> (For SoLID, we would need right base for this though, I am not sure if CFRP used for LHCb can work.)
>> There are some literature showing heavy gas can be transparent at this region if it's free of Q2 and H2O
>> So testing PMT at this region would be very interesting.
>>
>> Zhiwen
>>
>> On 8/30/2016 4:26 PM, Garth Huber wrote:
>>> 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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>>>>>>
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