Members: Yuhang and Tomura

On 09 December, we found that the end mirror of the filter cavity had relatively larger variation in its pitch motion. As refer to in elog 428, the normal angular variation for the end mirror pitch with the loop closed was 3-4 urad. However, values we found there were 6-7 urad. As for the other mirrors (PR, BS, and IM), these values seemd decent or even better. We suppose this pitch noise on the end mirror can be one reason why we cannot lock the cavity although the beam seems to be well aligned. The reason of the noise itself is still unknown.