There has been some development work on a new metal triangular mode cleaning cavity (a la PMC) to be tested out in bridge (initially in the CryoLab).
What can a PMC to do?
* Acts as a (poor) length reference if we lock to it * Filters out the laser noise above the pole of the cavity * Gives a fixed reference point for the beam pointing and location w.r.t. the optical table * Turns beam jitter and frequency noise into intensity noise * Can be mounted on a base so that you can remove and replace it very accurately
Some Questions One Might Ask
* The initial LIGO PMC