[Solid_cc] WLS coated MAPMT performance question

[Brad Sawatzky]

Interesting, thanks very much for the plot.  The (test) PMTs I've seen
in the past have be quite cloudy -- I suspect your deposition method
for the LTCC must be more refined.

If you have it, I would be interested in reading a technote or
equivalent about the CLAS LTCC application.

All the best,
-- Brad

On Mon, 29 Aug 2016, Sylvester J. Joosten wrote:

> Hi Brad,
> 
> To answer your first question:
> 
> When applied through vacuum deposition, the p-Terphenyl layer is
> barely visible - it mostly makes the PMT face look less glossy due to
> slight surface irregularities. Large degrees of cloudiness are
> indicative of crystallization, which *will* decrease the optical
> transparency.
> 
> We coated and tested 200 5-inch PMTs for the CLAS LTCC, and we
> performed precise gain measurements between 200 and 400nm with a
> monochromator. I included the results of such a measurement in the
> attachment. The measured gain is compared to the a theoretical
> calculation for a 110ug/cm^2 coating. Above 320 nm, the performance of
> uncoated and coated PMTs is identical, while below 320 nm the coated
> PMT performs significantly better. At no point did we measure any
> performance degradation.
> 
> Regarding the timing:
> 
> We measured a 2ns delay due to the WLS with a narrow time
> distribution. Light above 320nm does not interact with the WLS and is
> therefore not delayed. While I don’t think this is a big problem due
> to the 1/wavelength^2 dependence of the Cherenkov spectrum, I do agree
> we need to take this into account when designing our trigger
> (especially if we are thinking to use an ultra-narrow window).
> 
> Cheers,
> Sylvester