1. Gas measurements and CsI photocathode studies at WIS Ilia Ravinovich November 2002 Weizmann Institute

2. Gas measurements at WIS Test cell D2 MC PMT-1 PMT-2 Beam splitter LiF LiF window Detector Ar input Ar output CF4 input CF4 output Gas output The system comprises a H20 FUV monochromator (100-500 nm), a Deuterium lamp (115-400 nm), PMT-1460 (115-320 nm) and LiF windows (cut-off 105 nm). The transmission is determined as CF4/Ar ratio normalized to Ar/Ar ratio.

3. CsI photocathode studies at WIS D2 MC PMT-1 Beam splitter LiF CF4 output The CsI photocathode (2500 A) was deposited on a polished stainless-steel substrate, pre-coated with a 1000 A thick Al layer. A positive voltage was applied to a mesh electrode placed at a distance at 3.5 mm. Exposure to air < 10 min. CF4 input +HV A CaF2 window The CsI photocathode was prepared on 15.11.2002 and since then is continuously operated in vacuum and in CF4 atmosphere. The photocurrents are stable and well reproduced after several cycles vacuum-CF4. The CsI photocathode is not destroyed by CF4! Mesh CsI

4. Next steps at WIS D2 MC PMT-1 PMT-2 Beam splitter LiF Detector CF4 input CF4 output Gas output The idea is to use a single monochromator both for transparency monitor and CsI absolute quantum efficiency measurements. LiF window PMT-3 Rotate UV mirror (splitter) LiF window +HV A A Mesh CsI