Input Mode-cleaner
2021
Task list
- IMC LSC
- IMC ASC (2021/07/29)
- When COM and DIF loops are closed with high UGF, they may not be closed properly due to saturation, so review the loop design.
Calibrate all sensors associated with IMC ASC.
- First, we roughly check whether the angular fluctuation of the beam on IMMT1 meets the required value when the ASC is inserted in the configuration with one QPD of IMMT1 TRANS.
- Add a roll-off filter at a few Hz to keep the COM PIT noise out. This is because the PIT noise is visible from 30Hz to the lower frequency range of the IMMT1 TRANS QPD signal.
- Since the 12 and 13 Hz frequencies seem to be overdamped, and sensing noise is introduced, check to see if a peak at that frequency is really visible in the error signal. If you can see the peak at that frequency in the error signal, control it to remove it. If not, add a roll-off filter.
- Align the IMC and center all QPDs before measuring the sensing matrix, etc. Before taking alignment, take references. The way to do this is to turn on the ASC once and then turn off the input only, and the integrator will stop at the beam position when the ASC is on. Record the position.
- Put the transfer function of the DC centering loop into klog.
- When the ASC is turned on, the fluctuation of the DC light intensity becomes smaller, but this effect is different when the alignment is good and when it is bad, so check if the DC light intensity spectrum changes when the alignment is good and when it is bad.
- Measure the coherence between the signal of the TRANS QPD and the control signal. If the WFS is shaking due to jitter in the incident optical axis, the shaking should appear in the TRANS QPD signal of IMMT1.
- To completely determine the optical axis, the current sensor alone does not have enough degrees of freedom, so we need to add another sensor.
Hold regular meetings for reporting.
- Completely misalign the IMC and measure the RF spectrum and the DC spectrum of the reflected light from the MCI as seen by the REFL WFS.
- It is strange that the signals of COM and DIF, which are supposed to be different degrees of freedom, have almost the same magnitude when viewed by MCE TRANS QPD1 and 2. Recheck the measurement of the sensing matrix. It might be better to re-profile it.
- (After lock Xarm cavity) Calibrate the control signal of the arm resonator to the frequency noise and check if it remains the same with and without the IMC ASC.
Meetings
- 210818 IMC ASC weekly meeting
- 210729 IMC ASC review
Measurements
Finesse of IMC : k-log#17989 k-log#18002