Alexa, Evan

Daniel and Rana have pointed out that it doesn't make much sense to use AS_A_RF45 as a sensor for controlling the angular DOFs of sideband-locked PRMI/DRMI: the carrier is (intentionally) not resonant in these configurations, meaning that the 45 MHz RF signal is dominated by the 45 MHz sidebands beating against a weak (and potentially spatially junky) carrier signal. What we want instead is a signal which involves some sort of beating with the 9 MHz TEM00 mode, since this is resonant inside sideband-locked PRMI/DRMI. We propose to use AS_A_RF36 to feed back onto BS M2, since the 36 MHz signal involves the beating of the 9 MHz sidebands with the (co-resonant) 45 MHz sidebands. This is what is used at LLO (see Den's slides at G1400981).

We've done the following to prepare AS_A_RF36Q for use with the ASC loops:

• With no beam on AS_A, we zeroed the dc counts appearing on each segment.
• With Dan's help, we closed the ASC DC centering loops for AS_A. Originally these used the OMC QPDs to provide the error signal, but now they use AS_A DC.
• Then we excited the BS pitch by sending a 5.3 Hz, 3000 count excitation into H1:SUS-BS_M2_TEST_P_EXC.
• We demodulated each of the eight RF36I/Q signals at 5.3 Hz, and then adjusted the demod phases to put all the power in Q.

To proceed from here, we need to:

• Balance the relative amplitudes of the segments
• Adjust the gains of the ASC loops in order to compensate for any gain difference between RF45 and RF36.
• Improve the gains/shapes of the loops.