[Valera, Stefan, Masayuki, Yutaro, Yuta]
To check if the conjugation effect discussed in klog #9388 is correct, we locked PRX without Xarm and with Xarm.
We observed a reduction of p-pol with Xarm locked, as expected.
Locking configurations
Locking configurations are in LSC_LOCK guardian.
PRX is locked with REFL RF135, Xarm is locked with analog REFL RF45.
We did not used ALS.
After locking PRX on sidebands, we just turned Xarm lock on and waited ~30sec to acquire lock.
Result
Attached StripTool screenshot shows DC powers at different sensing ports when transitioning from PRXarm to PRX on carrier. Below is the summary of the build-up for s-pol and p-pol in each configurations.
PRX PRXarm
K1:CAM-POP_SUM 4.6e6 4.4e6 (camera pixel sum of POP Spol)
K1:CAM-POP_P_SUM 1.5e7 7.7e6 (camera pixel sum of POP Ppol)
K1:ALS-X_ARM_INPUT_OUT 12.3 4.0 (forward POP P-pol)
The amount of p-pol inside PRX cavity is attenuated by a factor of ~3 when Xarm is also locked.
From p-pol reduction, we might expect s-pol increase, but the amount of s-pol inside PRX cavity is actually slightly reduced (~5%) since Xarm reflectivity is lower than ITMX reflectivity due to Xarm losses, and cavity build up will be smaller.
REFL (s-pol power) is also slightly increased with Xarm locked since Xarm reflectivity is lower than ITMX reflectivity due to Xarm losses, and PRX cavity will become more undercoupled.
The beam shape of POP p-pol is also better with Xarm locked (compare camera screenshots when PRX and PRXarm).
During the experiment, we also measrued the build-up gain of PRX from single bounce from ITMX at the POP table (POP PDA1 DC). The DC signal is as follows:
| ITMX single bounce (PRM misaligned) | 3.5 |
| PRX locked on carrier resonance | 8.5 |
| PRX locked on f1 resonance | 2 |