Yaochin and Yuhang

We tried to match BAB to the filter cavity last Friday. However, we found the beam is quite misaligned. And we have a bad mode mismatch.

Later, we figured out that there are two different reasons causing this problem.

1. Change of Faraday isolator. The length of the old FI(IO-3-1064-VHP) is 114.3mm. The length of the new FI(FI-1060-5SC HP) is 58mm. This length difference is not negligible and will change the mode matching condition.

2. Change of lens1 position. This lens1 is the lens just after OPO transmission. It is the common lens for FIS and FDS path. After the installation of the new Faraday, the matching condition for FIS is changed a lot. To characterize FIS, we must move the common lens.  

Anyway, we should first match BAB to AMC. 

We will measure again the beam parameter and check the position of lenses after matching BAB to AMC.