[Cheryl, Giacomo]
Today we were finally able to route the parking beam through its intended baffle and viewport. With this result in hand, we gave a first quick try at a power budget.
The short version of the story is that at the parking viewport we measured about 60% of the power that reaches MC1, or 86% fo the power coupled into the IMC (due to a rather sloppy alignment).
The beam was measured at the following locations (power in mW, IMC locked unless otherwise specified):
| IMC REFL (IMC unlocked) | 174 |
| IMC REFL* | 49 |
| IM1 transmitted | 0.053 |
| IM4 forward transmitted | 0.0165 |
| IM4 backwards transmitted | 0.272 |
| Park | 106 |
* The IMC REFL with the IMC locked is estimated from the scaling of the REFL PD signal between the locked and unlocked status. At the time of the measurement the alignment was not great and the visibility was about 70%.
Due to lack of time, we did not measure the beam power inside the PSL.
When compared to the power effectively coupled into the IMC (the difference between IMC_REFL locked and unlocked), the power at the parking beam is 86%. For comparison, during the last power budget at LLO, a value of 90% was found.
Also, looking with an IR viewer into the chamber from one of the side viewport, we can see a bright beam on the adaptive optic dummy in front of IM4. It is not clear if it is a ghost beam, but probably not given its brightness. Tomorrow we will try to tune the alignment and see if and how much power we recover in the parking beam.