I think I have told a lie in the last meeting -- the measured sensing matrix doesn't look similar to what Optickle predicts.
Smells like something is very wrong.
Measured sensing matrix
The measured matrix are shown in the diagram below.
The lengths of arrows corresponds to the signal strength in unit of V/m. The radial axis in in log scale.
The angle of arrows corresponds to their best demodulation phases.
Some obvious things:
- REFL11 : The separation angle between MICH and PRCL is narrow and it is far from the ideal 90 degree. This doesn't agree with the simulation.
- REFL33: The MICH and PRCL signals are almost degenerated in their demodulation phase.
- REFL55 : It shows non-90 degree separation. This doesn't agree with the simulation.
- REFL165 : The separation is close to 90 degree, but the signals are small. And I am not sure if the MICH signal is real or just noise.
- AS55 : Somehow it shows a nice 90 degree separation, but this result doesn't agree with the simulation.
Expected sensing matrix from a simulation
For a comparison here is a result from an Optickle simulation.
This time the radial unit is W/m instead of V/m, but they are qualitatively the same unit.
The radial axis is in log, so when it says 2, it means 10^2 [W/m].
Simulation setup:
loss per optic = 50 ppm
Measurement
- Locked PRMI with the carrier anti-resonating in PRCL.
- Adjusted the control gains for both the MICH and PRCL control to have UGFs at ~ 100 Hz.
- Put a 30 dB notch filter in each control servo at 283.1 Hz where an excitation signal will be.
- Excited PRCL and MICH at different time via the realtime lockng in the LSC front end. The amplitude is 1000 counts and the frequency is at 238.1 Hz.
- For the MICH excitation, I have coherently and differentially excited ITMs
- Used DTT to take a transfer function (transfer coefficients at 283.1 Hz) from the lockin oscillator to each LSC demodulated signal.
- Including AS55I/Q, REFL11I/Q, REFL33I/Q, REFL55I/Q and REFL165I/Q.
- Calibrated the obtained transfer functions from unit of counts/counts to V/m using the actuator response (#5637)
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I have measured the sensing matrix of PRMI.
It seems that the MICH signal in the 3f ports (REFL33 and REFL165) were quite tiny, and because of that it is very tough to use them for the actual MICH control.
The data is coming soon.
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