# Simulation meeting 2022 Jan 27 15:00

Zoom2: https://zoom.us/j/6676627462

## Participants

Marc Eisenmann, Matteo Leonardi, Yoichi Aso, Yuta Michimura, Haoyu Wang

## Agenda

### Updates from Projects

- Birefringence simulation
- Marc suggest we need to recenter the TWE maps before calculating theta map. We can use markers on TWE maps to find out the rotation center of the mirror.
- The current alpha-minus map used for simulation has too large PV value (300nm). In this case, we need a lot of higher-order modes to do the simulation, which can take weeks to calculate. So we must unwrap theta and alpha-minus.
- The current software FINESSE version 2 cannot apply amplitude reflection index to mirror. It uses power reflection index, which has sign problems to simulate the birefringence effect. We are going to use FINESSE version 3, which allow simulators to use user defined maps and the calculation of mirror maps in FINESSE 3 is improved.
We are currently simulating round-trip loss in one arm cavity when birefringence is considered with the MZ model with fixed parameters (without maps), and compare it with Michimura-san's calculation calculation.

- Birefringence characterization of Spare ETMY in NAOJ
- With careful calibration for the centering and rotation of TWEs, the theta map looks quite smooth now after unwrapping. But there are still some sharp features.
- Marc is going to measure delta-n again with normal incidence, and compare it with calculation from TWEs.

- Other business
- We are going to change the frequency of simulation meeting to monthly as the content is overlapped with the MIR meeting, integration meeting and KAGRA filter cavity meeting.