[Jason, Masayuki]

• The laser power was increased to 1 W, and a beam dump campaign for ghost beams was carried out. First, a mirror-mount beam dump plate was installed on the JM2 mirror mount.
• Next, a beam dump to catch the AR reflection from the EOM was installed next to JAC_L1.
• Then, the s-polarized beam separated by the EOM was dumped between JAC_L2 and JAC_L3. Since a balance mass was present in this area, the beam dump height had to be adjusted. A dog clamp was inserted between the post and the beam dump to raise the height.
• When observing the beam between JAC_L2 and JAC_L3, multiple vertically separated beams were seen. At first, this was suspected to be a reflection returning from the HAM2 septum viewport; however, the beams did not disappear even after blocking the downstream path, indicating that this was not the cause. The most likely origin is multiple reflections from JAC_L1, although this has not been confirmed.

We still need to find the back reflection beam from the septum viewport, and discuss what we will do for the vertically separated beams.