# Minutes of the ISC Meeting on 2015/3/13

Date/Time: 2015/3/13, 13:00 - 15:00

Location: SeeVough

Participants: Hirose, Michimura, Yamamoto, Arai, K. Yamamoto，H. Yamamoto，Arai，Miyakawa，Kokeyama, Somiya, Ando, T. Saito，Kawabe, Aso

## Main Conclusions

#### AR IBF

- No compensation for the index of refraction inhomogeneity is unacceptable.
- We should give a specification for the RMS fluctuation of n to the polisher.
- A concrete number for this specification will be decided based on more simulations.

#### Output Optics

- Even for bKAGRA1, we need to use OFI, OMMT and OMC (all of them).
- We need to try to find a design with less number of output chambers for cost cut.
- Relaxing the requirements for IMMT and OMMT mirrors should be considered for cost reduction.

## Action Items

- Perform simulations of the ITM substrate inhomoeneity with various maps to decide on the requirement for the RMS of n (Hirose, H. Yamamoto).
- Perform simulations with RSE (Hirose, H. Yamamoto)
- Calculate the HOM spectrum at the AS with Finesse with simple ITM lenses included (Somiya)
- Find a configuration for the output optics with less number of output chambers (Somiya).
- Check how much IMMTs can be moved to compensate for the ROC error (Aso).

## Discussion memo

#### AR IBF

- The 45MHz RFSB power decreases significantly in the PRC when the RMS of n fluctuation gets larger (roughly over 20nm). We need to give a spec number to the polisher.
HOM spectrum at the AS port can be calculated with Hirose-san's simulation. -> Useful for the OMC design.

- We need to simulate with many random(?) inhomogeneity maps to see the worst case.

#### Output optics

Shall we change OMC between bKAGRA1 and bKAGRA2 ? -> Quite likely. We should develop the first OMC focusing on bKAGRA1. If it turns out to be good enough for bKAGRA2, we will continue to use it. If not, we will make a new one.

We need to check if reasonable control signals can be obtained for bKAGRA1 with PRFPMI. -> A/I for Aso.

- A back of the envelope calculation shows that good vibration isolation is needed for output optics. Just putting on the ground is not OK.
- We need to find a way to squeeze in OFI, OMMT, OMC to less number of chambers, utilizing the fact the SRM chamber is empty for bKAGRA1. (We have to be careful because there is no bread board with stack in SRM chamber by default).