Stefan, Koji, Kiwamu,

We newly installed a L2P correction filter on BS which reduces the coupling to the bottom stage pitching from the penultimate length actuator drive.

Stefan completed the L to P and P to P measurements on BS yesterday. Then Koji fitted the data using LISO and I punched in the fitted poles and zeros of the ratio L2P/P2P in foton and loaded the filter in M2_DRIVEALIGN_L2P. We did a quick test in which we had a big excitation in the M2 length drive and monitored the pitch motion by the oplev with and without the L2P correction. It looked successful although we did this test at only two frequencies, namely 1.1 and 0.8 Hz, because a Y to Y measurement was running in background which we didn't want to screw up at that moment. The coupling looked successfully reduced at least by a factor of 10 at both frequencies as far as we can observe it on a StripTool screen. Note that in order to get the cancelation right, the gain of the L2P  correction chain needs to be -1. If one wants to further test the performance, he or she should run a swept since measurement extensively.

* * *  the L2P correction filter * * *

- - - - freq [Hz]   Q - - - - - -
pole 0.3737768342347  3.4267960418
pole 0.4822474954282  7.0937407121
pole 1.1164786260     9.7341833818
pole 2.1443263848     3.2444753770

zero 0.4313822619174  2.1809027959
zero 0.7477704984560 224.3944177073
zero 1.7628959088     1.1355062310

gain factor -0.0108000650535