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Quantum Efficiency measurement system for large area CsI photodetector . Francesco Cusanno INFN Roma I Gruppo Sanita’ on behalf of Hall A RICH collaboration. TJNAF - Hall A RICH Evaporation system The Q.E. measurement system: Measure principles and procedure
Quantum Efficiency measurement system for large area CsI photodetector
INFN Roma I Gruppo Sanita’
on behalf of Hall A RICH collaboration
, 0.5 cm
TJNAF - Hall A RICH
We built a proximity focusing RICH for Hall A at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab)
Rich in Hall A
RICH Phase space in Hall A
Cu – Ni – Au pad layers
10-6 mbar vacuum, 2 nm/s CsI deposition at T = 60 ºC (CERN experts indications). Vacuum - heating conditions start 15 – 24 h before evaporation. A post-evaporation heat treatment is done for 12 hours.
Rotating mirror (CaF2)
UV source box
The ratio A2/A1 = Q.E.(CsI)/Q.E. (PMT), indeed the wire chamber is in the vacuum (no charge amplification) and the anode and grid voltage allow to work in full collection regime for the chamber (and the PMT dynodes and anode are connected together to ground, so no charge amplification for PMT too; PMT supply is 78 V).
A3 current (PhotoDiode in the optic box) monitors the UV source stability.
Hamamatsu L2D2 lamp (C7860 power supply) 161 nm spectral peak; 3 filters (Acton Research Corporation),
~ 20 nm FWHM wide, centered at 160 – 185 – 200 nm)
Filter rotating switch system,
(6 position, one is Al disk)
N2 flow tube
Hamamatsu L2D2 Deuterium lamp
Peak 158.80 nm; spread: 25.20 nm FWHM
Peak 198.40 nm; spread: 23.40 nm FWHM
Q. E. (%)
PMT- source convolution
CsI - source convolution
(lamp + filter)
Q. E. (%)
We use Electron Tubes Limited (ETL) 9402B PMT, Q.E. is known by ETL (single PMT) datasheets.
ETL 9402B characteristics
9402 S/No. 38 PMT Q.E.
CsI Photocathode (0 V)
Grid (0 V)
Anode wires collect electrons from the CsI plane
The grid wires ‘stop’ electrons on the anode
Anode wires are 20 mm diameter, grid wires are 50 mm diameter, anode and grid wires are crossed.
Wire distance is 4 mm.
Chamber collecting area is 50 mm x 50 mm (light spot is smaller, ~ 10 mm).
We get a complete Q. E. map; in this case 1 bad spot (~ 1 cm2). If bad results we can repeat the evaporation (soon).
Good uniformity on all the PC (total spread:
21.7 % -24.4 %, apart the bad spot; average
Q. E.: 23.7 % ).
Average Q. E. at 200 nm: 5.5 %
Same pattern at 185 nm too,
Average Q. E. at 185 nm: 11.6 %
15 % error bars are plotted
0; 0; 1.2 g; 1.2 g
Air exposure and reconditioning
22 h. air exposure (19.5 ºC, 41% relative humidity), 27 h. pumping has a small effect; 12 h. heating restore about 1/3 of the loss.
Outgassing and reconditioning
25 not-pumping d., 0.25 mbar, reconditioning: 12 h. pumping + 14 h. heating 60ºC; second (longer) heating has no effect.
6 not-pumping d., 0.013 mbar, has similar effect than after pumping reconditioning in the previous case (50% loss)
Possible interpretation is the ‘outgassing’ of organic particles from the substrate (it is cleaned by organic solvent before evaporation).
Also the system can perform thickness, air exposure, post heat treatment dependence study.
Extrapolating the thickness dependence results (adding the ‘standard’ 300 nm result) it possible to expect higher Q. E. at higher thickness
0; 0; 1.6 g; 1.6 g
2 mm Au
10 mm Ni
(7 mm requested)
Support and temperature dependence