TCS works

(Viviana, Alessio)

This entry is to report on the activities performed on wednesday afternoon and thursday morning.
On wednesday 27, we worked on the polarizer issue (see NI TCS bench works):
we performed a test with the IR cameras. The set-up or the
measurement is shown in figure 1. On the North bench, with the new
laser, the effect is still there. We than made the same measurement on
the West bench and this effect is not seen. We suppose that the
cause is the new laser installed on the North bench, so next week we'll
replace it with the other spare.
On thursday 28, the activity was focused on the intensity
stabilization, mostly to investigate the cross-talk between the two
benches. We closed the intensity stabilization on both benches and the
noise spectra were showing common lines with very high coherence. The
effect is due to the beating between the RF signals of the laser RF
drivers (see Fixing 75Hz line) re-introduced by the AOM cables and/or RF drivers.
We tried to decouple the benches by changing the cabling of the AOM
drivers, but no effect was visible. At last, we moved the WI laser RF
driver from the TCS room to a place close to the WI acoustic enclosure,
as far as possible from the NI laser RF driver: the amplitude of the
common lines decreased. Next week we'll try to improve the shielding of
the lasers RF drivers.