To measure the losses in the chain containing the EOMs, the Faraday and the IPC1 on EIB, the power was measured with a calorimeter, preceded by a f=-50mm devergent lens (newport KBC043)
- Before the EOMs, the measured power was 32.6 W at 12:58:30 UTC.
- After the EIB_M5 mirror, the power was 24.0 W at 14:01:00 UTC
We tried to measure the power without the divergent lens,
- Before the EOMs, P=42.1 W at 14:13:50 UTC
- After EIB_M5, P=30.5 W at 13:02:45 UTC
In every measurements, the output voltage of the PMC_TRA photodiode was stable around 0.53 V. The BPL was closed. It appears that the presence of the lens changes the measurement by 25%, probably due to an absorption or an uncoaded surface or the variation of the beam size on the calorimeter. So we decided to use another lens f=-30mm.
- Before the EOMs: P= 42.8 W at ???
- After EIB_M5 P=30.1 W at 14:31:40 UTC
The estimated losses of the whole chain is 30%.
We recentered the beam on the BPL quadrant, with the PMC cavity locked, we closed and open the BPL loop, so the piezos are roughly at the position that send the beam into the EOM. Then we move the QN quadrant vertically until the Y signal is cancelled, and the QF until TX signal is cancelled. Then all the setpoints of the BPL are set to 0 urad and 0 um.
After that,we tried to rotate IPC1 while measuring the power after EIB_M5 in order to maximize the measured power. We managed to reach a power of 34.6 W, which corresponds to a 20% loss. Then we changed the horizontal shift setpoint (X_SET signal) in order to maximize the power measured by the calorimeter. By seting X_SET to -200 um, we reaached a 35.6 W power. Which correspond to a 16 % power loss. The others degrees of freedom remains untouched.