The CGH on its mounting assembly was inserted into the hole in M3 today. It can be seen through the lower section of the SAC framework (aka the birdcage) when the rubber sleeve surrounding the SAC is lifted up.
Neat to finally get to see M3 properly as well!
The SAC Reference Mirror's a small flat mirror that bolts onto the back of M4 & is used to align things with the optical axis of the SAC. We attached that in order to adjust the tip & tilt of the interferometer so that we'll be able to pick up a beam returning off the CGH. A rather cute little parasol had to be employed to prevent the reference mirror sending an extra beam straight back up that would swamp the CGH return.
The angry volcano's calling for a SACrifice...
To be able to reach M3 & the CGH, the Faro Arm sits on a lower perch than its usual one & wears an extended probe on the end.