Figure 1 shows the “before” to “after” improvement in DARM. In addition, the figure shows the large decrease in jitter in the IMC WFSs. Both are included because the coupling to DARM varies, but the jitter signal is consistent. 

Figure 2 shows the original and the new mounts for the piezo mirror. The main mechanical changes are: 1) the collar is glued into the U200 mount instead of pressed by the usual single set screw. This stiffens the pitch and yaw motion of the piezo and collar around the connection to the U200 mount. 2) I added a “flying buttress”, bolted to the alternate U200 connection point on the side (inset photo). This is to stiffen and damp the pitch and yaw degrees of freedom around the single connection screw between the U200 mount and the base. 3) I added damping material to the new mount. 4) We shortened the lever arm of the massive mirror, while keeping the mirror in the same place, by moving the U200 attachment point forward to an alternate threaded hole in the base.

The main resonance moved from 260 to 350 where it overlapped with the largest resonance of the top periscope mount, so we brought it back down about 15 Hz by adding moment of inertia with damped clamps. It is now much damped and lying on top of one of the lower amplitude modes of the top mount.

In addition, we noticed that the beam was very close to the edge of the safety tube (second page of Figure 2). We moved the beam further from the edge by reducing the length of the tube by a couple of inches (the tube is angled relative to the beam) and by shimming the inner tube in the telescoping assembly. We replaced the white clean room tape, that was locking the telescoping assembly, with Kapton tape. The safety tube is a couple of inches shorter but still extends over the edge of the table (see figure).

Kiwamu I., Rick S., Robert S.