Some more details of the yesterday shifts:
Waveplates
- EQB1 HWP position to equalize LO and BAB: 109470
- SQB1 HWP1 position to maximize the incoming beam toward FLT: 36297
- SQB1 HWP2 position to send all the reflection back to EQB1: 82525
- Final position of SQB1 HWP2 in order to have a weak transmission after SQB1 FI 83025
N.B in order to minimize the homodyne detection losses we had to change the polarization axis from poth the waveplates. To change polarization we have to do about 27000 steps whereas to change axis about 54000. The waveplates have a lot of hysteresys thus these number are not an absolute reference.
BAB and SC Mode contents:
Afrer the alignment of the cavity we checked the power of TEM 00, TEM 10 and TEM 20 of BAB and SC. During the measurement we realized that we had the cavity well aligned on SC and the SC and BAB not well superposed. Afrer the measurement we aligned the BAB into the cavity with IR_M3 and M5 then we aligned the SC into the cavity using SC_M1 and SC_M3.
We found the following results:
| BAB [V] | SC [V] | AOM SET BAB [V] | AOM SET SC [V] | |
|---|---|---|---|---|
| TEM00 | 1.99 | 12.62 | -0.0081 | 0.0676 |
| TEM10/01 | 0.157 | 0.11 | -3.63133 | -3.555 |
| TEM20/02 | 0.011 | 0.06 | 3.4652 | 3.541 |
Attached a plot of the AOM scan between -4V and +4V with SC and BAB shutter open.
We found the sidebands at the following AOM set:
- SC Lower: -1.38 V (about 0.6V of transmission)
- SC Upper: 1.51 V (about 0.6V of transmission)
- BAB Lower: -1.952 V (about 0.12 V of transmission)
- BAB Upper: 2.09 V (about 0.12V of transmission)
To be sure we need to check id the -1.952V and 2.09V sidebamds are due to the modulation of the BAB inside the AEI Box. We will check it soon by switching off before SC sidebands and after by switching off the SC itself.
