[Dsg-rich] all RICH Mirror 4 samples' reflectivity measurements complete

[Marco Mirazita]

Hi Tyler,
thank you for the data.
During the RICH meeting last friday, I presented some analysis of the 
data measurements on the samples of mirror 3, the file is here:
https://clasweb.jlab.org/wiki/index.php/2017_RICH_meetings
I now included the latest data, but my conclusions don't change.

The very first measurement on the control mirror was consistent with the 
known results from years ago.
However, in the measurements on our samples I found large variations in 
the response of the two photodiodes, bigger on photodiode A than on B.
This is strange (with respect to A, the B should see also variations on 
the reflectivity) and seems to indicate some instability of the system.

Thus, I would like to understand a bit better the system before changing 
anything.
As far as I can understand, possible source of instability could be:
- alignment problems: but according to the note, the system should not 
be sensitive up to few mm of misalingment.
- Instability of the light source

My suggestion is to take the following measurements, if you or someone 
from the DSG is available for that:

1) Verification of the stability of the calibration measurement
Align the system for the calibration runs, then take a set of 
calibration measurements say every 1 hours or so during one day (i.e. 6 
or 7 measurements), without touching anything between the measurements.
Please take note of the time you turn on the lamp and the time passed 
since then for every run.

2) Verification of the stability of the reflectivity measurements using 
the control mirror
Repeat the cycle of calibration and reflectivity mesurerement few times 
during one day:
- align the system for the calibration run
- take calibration data
- install the control mirror and align the system for reflectivity run
- take a reflectivity run
Once the mirror has been installed the first time, it should not be 
touched anymore for the next measurements, the alignment procedures 
should involve only the photodiode B. Again, please take note of the 
times.

This measurements should take two days,
Once we have these data, we could discuss what to do next.

Best regards,
Marco


Il 2017-07-14 23:09 Tyler Lemon ha scritto:
> Hello,
> 
> Attached are the Excel sheets containing reflectivity measurements for
> RICH Mirror 4 Samples 26, 27, and 28.
> 
> As we did yesterday, we took one calibration run at the beginning of
> all tests and then took two test runs for each mirror sample. All runs
> scanned wavelengths from 300 nm - 650 nm in steps of 10 nm.
> 
> Best regards,
> 
> Tyler
> 
> _______________________________________________
> Dsg-rich mailing list
> Dsg-rich at jlab.org
> https://mailman.jlab.org/mailman/listinfo/dsg-rich