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Dmass and Koji
Last night we engaged the MZ and the ISS paths with the analog servos.
When I went to the lab, the MZ was locking but the ISS was oscillating at around 70kHz.
We reduced the gain of the last stage by a factor of 3, the oscillation was removed.
Dmass planned a comprehensive set of the measurements and is expected to reveal it on the e-log.
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These are the measurements I have planned, in order:
- Look @ green difference versus IR difference on a scope, use the Lissajous figure to calibrate the phase response
- Take Spectra of the IR and Green difference (now calibrated to phase) with the MZ locked and free, and see if the phase in the MZ locked state changes with ISS on/off
- (The green difference / green phase is my out of loop measurement of the IR phase - which I am locking - so I should be able to infer whether or not I am seeing excess noise in the green. I can figure out whether it is explained by the known sensing noise later)
- Do a series of four arm blocked measurements where I use one IR PD to do ISS, use the other as an OL PD, and then compare this to the green PDs (which are also OL), and see if I see excess intensity noise
- Consider whether or not I want better phase numbers closer to the UGF of the Mach Zehnder - PZT system. If I do, and I think I can win by doing some subtraction - AC couple into the DAQ (with SR560s), and then just record those and apply the existing frequency domain subtraction algorithm.
- Think about what exactly I should do for trying to get phenomenological transfer functions of Temperature / RIN into phase noise. (I still need to doodle out a setup here)
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