1. Tuning the MICH-->PRM output matrix element
   • Locked the PRMI with the carrier field resonant in the PRC.
   • REFL11 used to control PRCL, AS55 for MICH.
   • Turned on the sensing notches in the control filter bank. Drove a line in MICH at 311.10 Hz.
   • Tweaked the MICH-->PRM matrix element to minimize the coupling witnessed.
   • As shown in Attachment #1, the minimum coupling was found to be at the value -0.34 (the old value was -0.2655).
   • The minimum was very sharp. A 1% change from the optimum value increased the peak height by > x2. Is this reasonable?
2. Some sensing matrix measurements: After tuning the output matrix element, I locked the PRMI (ETMs misaligned) in four configurations:
   • PRMI locked with carrier resonant. REFL11_I used for PRCL control, AS55_Q used for MICH control.
   • PRMI locked with sidebands resonant. REFL11_I used for PRCL control, AS55_Q used for MICH control.
   • PRMI locked with sidebands resonant. REFL11_I used for PRCL control, REFL165_I used for MICH control (based on sensing matrix measurement and offsets from previous config).
   • PRMI locked with sidebands resonant. REFL33_I used for PRCL control, AS55_Q used for MICH control.
   • The attached GIF shows the evolution of the demodulated sensing lines as we move through configurations.
      
   • The actual PDFs are attached as a zip, Attachment #2.
3. PRMI locking with arms under ALS control
   • The arm cavity lengths were controlled as usual with ALS. This system needs some noise budgeting.
   • I set the CARM offset to -8 (arbitrarily chosen, approximately equal to 20nm, but anyways well above the cavity linewidth).
   • Then I re-aligned the PRM, and attemped to lock the PRMI using the 3f settings determined with no arm cavities --> no success.
   • Tried locking using the 1f error signals instead - in this config, the lock could be established.
   • However, I saw that there was significant light on the AS camera, and I had to put in an offset into the MICH loop to make ASDC go as low as possible.
   • I guess it is possible that the ALS control wasn't precise enough and the leaked light to the dark port was because of differential reflectivity of the arm cavities?
   • Anyways, I ran a sensing matrix measurement with the interferometer in this configuration, and I found that the MICH signal in REFL165 had rotated significantly.
   • I also found that the 3f DC offsets in this configuration were ~5x greater than what was the case for the lock with no arm cavities.

This is as far as I got last night. The first step is to see how reliable the settings determined last night are, today. I don't understand how changing the output matrix element can have brought about such a significant change in the MICH/PRCL separation in all the RF photodiodes.