On Jan. 15th I replaced IO_MB_M3, which is in the main beam, in the IO path on the PSL.

After Robert added the tuned damper, I replaced the optic, and realigned the IMC_IN beam, using my GigE cameras, and the single bounce off of MC1 to the IMC WFS, and the results are that the IMC optics changed 5urad or less in each DOF from before the optic swap, results described in detail in alog 46436.

Robert found the jitter peak from this optic was greatly reduced, described in alog46494.

I've cleaned and inspected the optic that was removed, and found 6 small dings in an arc on the front surface, ranging from about 3mm to 16mm from the center of the 2 inch optic.

These damage sites are consistent with what was likely considered minor impact, and with the scattering from the optic.

I can't yet confirm that the scattering has been reduced with the new optic, as there was no time to evaluate.  I will evaluate at the next possible opportunity.

The attached files show two views of the optic's damage, and those features that are on the front surface are circled in yellow.  Both files are ~8MB.