J. O'Dell, J. Garcia

Continuing with the diagonalization of the FMY M1 OSEMs, mechanical adjustments to the FMY top mass (M1) were made to further decouple the "F1" and "SD" OSEMs from the Yaw DoF.  The same sine wave excitation at 1.4Hz was injected to the "H2:SUS-FMY_M1_TEST_Y_EXC" channel with a 100ct amplitude. The expected contributions to the "Yaw" transfer function should be the "F2" and "F3" OSEMs with desired isolation of the other OSEMs ("F1", "RT","LF", "SD") at ~30dB or less.

Initial measurements indicated the "F1" OSEM to be ~10dB isolated from Yaw, with the other OSEMs at ~30dB isolation. Our reasoning was the "F2" and "F3" OSEMs were not in line with the center-of-mass of M1, causing a slight Pitch that would manifest itself in the "F1" OSEM response.  To lower the COM of M1, a 300g mass was added to the top of M1.  The OSEMs were then realigned to center the flags and the first pdf is the same measurement with this configuration.  The "F1" response is roughly ~20dB lower than "F2" and "F3" and the "SD" response about ~17dB lower.

"fmy_osem_diag_yaw_add_mass_300g_f1align_111005.pdf"

This promising result encouraged us to add more mass to lower the COM further.  A 100g mass was then added to M1. At this time, it was noticed the flag of the M2 LL OSEM was twisted and possibly rubbing against the OSEM photodiode sensor and/or LED source.  The M2 LL OSEM housing was removed, and the subsequent measurement is displayed on the second pdf.  The "F1" isolation is now at ~25dB and the "SD" OSEM now at ~29dB.  

pdf #2 - "fmy_osem_diag_yaw_add_topmass_400g_f1alignm2llosemoff_111005.pdf"

The flag for the M2 LR OSEM was noticed to be twisted as well, and it's OSEM housing was removed.  The current configuration of the FMY is the M2 LL and LR OSEM housings are removed, there is now 400g added mass to the M1, and the M1 LF and RT flags are out of range of their respective OSEM beam paths due to the added mass.