*****
To join or leave the confocal microscopy listserv or to change your email address, go to:
https://lists.umn.edu/cgi-bin/wa?SUBED1=confocalmicroscopy&A=1
Post images on http://www.imgur.com and include the link in your posting.
*****

I think the change in gain is fairly logical with temperature.  As
temperature increases electrons have more thermal energy and are more
easily liberated from the plates in the PMT which leads to higher dark
counts.  It stands to reason that this increased energy also increases
the average number of electrons liberated during the photoelectron
multiplication process.

In general the gain of PMTs is not stable, varying dramatically with
both voltage and age. If you want to do quantitative measurements over
a longer period of time, you probably want to be photon counting or
else use a SiPM or other more stable detector.

Mike

On Sun, May 7, 2023 at 9:14 AM Mark Cannell <[log in to unmask]> wrote:
>
> *****
> To join or leave the confocal microscopy listserv or to change your email address, go to:
> https://lists.umn.edu/cgi-bin/wa?SUBED1=confocalmicroscopy&A=1
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi Ben
>
> Interesting. Your result seems to be inline with other studies showing an increase in QE as tubes are cooled below RT although about 20x larger than I expected given earlier studies
> e.g. Fig 11, A. Lyashenko et al 2014 JINST 9 P11021
>
> I wonder if the large gain effect you measured could have been related to the system electronics e.g. K-d1 voltage, overall PMT supply voltage, I-V converter etc. rather than the PMT per se?
>
> However, the CERN student suggested that S/N went up with temperature... Could that different result be related to photon wavelength since the 633 nm photons apparently had barely enough energy to liberate a photoelectron (the author suggested the QE ~ 0.05%) so that an increase in temperature could improve photoelectron liberation in that regime? Once photoelectrons leave the photocathode their energy should be so high (~100 eV) compared to RT that temperature should only have small effects.  It's also possible to get artifacts using photon counters at very high count rates.
>
> Cheers Mark
>
>
> Mark B. Cannell. Ph.D. FRSNZ FISHR
> Department of Physiology, Pharmacology & Neuroscience
> School of Medical Sciences
> University Walk
> Bristol BS8 1TD
>
> [log in to unmask]
>
>
>
> On 06/05/2023, 05:13, "Confocal Microscopy List on behalf of Benjamin Smith" <[log in to unmask] on behalf of [log in to unmask]> wrote:
>
>     *****
>     To join or leave the confocal microscopy listserv or to change your email address, go to:
>     https://lists.umn.edu/cgi-bin/wa?SUBED1=confocalmicroscopy&A=1
>     Post images on http://www.imgur.com and include the link in your posting.
>     *****
>
>     There are many reasons to keep a microscope room as thermally stable as
>     possible, but stable PMT gain is one of them.
>
>     There was a lab group here who were trying to quantify fluorescence
>     intensity on a two-photon microscope, but they were getting a triangle wave
>     pattern with a 17 minute period.  By simultaneously monitoring the PMT gain
>     and ambient room temperature, we confirmed that the PMT gain was inversely
>     proportional to the room temperature.
>     https://bit.ly/3HFMayj
>     https://bit.ly/42wuPQK
>
>     Most surprising for me was that a 1°C increase in ambient room temperature
>     was sufficient to cause a 6% decrease in PMT gain.
>
>     It also turns out that this effect was previously published by a student
>     researcher at CERN:
>     https://cds.cern.ch/record/2278277/files/temperature%20dependence%20of%20PMT%20quantum%20efficiency.pdf
>
>     This is also something to keep in mind in poorly cooled rooms, where unless
>     the PMTs themselves are thermally controlled, the PMT gain will gradually
>     go down, which would falsely look like a decrease in fluorescence.
>
>     Cheers,
>        Ben Smith
>
>     --
>     Benjamin E. Smith, Ph. D.
>     Imaging Specialist, Vision Science
>     University of California, Berkeley
>     195 Weill Hall
>     Berkeley, CA  94720-3200
>     Tel  (510) 642-9712
>     Fax (510) 643-6791
>     e-mail: [log in to unmask]
>     https://vision.berkeley.edu/faculty/core-grants-nei/core-grant-microscopic-imaging/
>