Experiment in the night of Jan 26.
o The arm was locked for the IR beam and was aligned for it.
o The green was aligned to the arm
o The beat freq was observed with the RF analyzer and the webcam.
o Engaged the ALS servo
o Compared the fluctuation of the beat freq with and without ALS
o Scanned the beat freq in order to find an IR resonance
The beat freq was scanned. A resonance for IR was found.
However, the residual motion of the arm was not within the line width of the IR resonance.
To Do
- Improve the ALS servo (==>Koji)
- VCO noise characterization (==>Suresh is on it)
- Calibrate the PLL feedback (i.e. ALS error) into Hz/rtHz (==>Suresh)
- Calibrate the end green PZT fb into Hz/rtHz (==>Osamu is on it)
- Tuning of the suspension filters to reduce the bounce mode coupling.
DETAILS
o How to lock the arm with IR
- Coarsely align the arm without lock. Transmittion was ~300 with MCTRANS ~40000
- REFL11I is the error signal. unWhiten filter (FM1) should be on.
- Unlock the MC and null the error and the arm trans offset by running the following commands
ezcaservo -g -0.1 -r C1:LSC-REFL11_I_OUTPUT C1:LSC-REFL11_I_OFFSET
ezcaservo -g -0.1 -r C1:LSC-REFL11_Q_OUTPUT C1:LSC-REFL11_Q_OFFSET
ezcaservo -g 0.1 -r C1:LSC-TRX_OUTPUT C1:LSC-TRX_OFFSET
- Confirm the input matrix to pass REFL11I to MC path (why don't we use XARM path...?)
ezcawrite C1:LSC-MTRX_81 1.0
- Servo configuration
- For acquisition: Gain of 2. Only FM1 (1000:10) has to be on.
- After the acquisition (TRX>200): The gain is to be changed to 1. FM2 and FM3 can be turned on for the LF boost.
- Actuator matrix: connect MC path to ETMX and MC2
ezcawrite C1:LSC-OM_MTRX_18 1.0
ezcawrite C1:LSC-OM_MTRX_78 1.0
o How to align the green beam
- After the alignment I went the end and aligned the last two steering mirrors.
o The beat freq monitor
- Put the RF analyzer at the RF splitter of the RFPD output.
- Used Zonet webcam (http://192.168.113.201:3037) for the remote monitoring
o How to engage the ALS servo
- Preparation:
- VCO PLL feedback comes to X_FINE path.
- Put an offset of -850 to cancel too big offset (when the VCO is unlocked)
- Use Y_FINE channel for the offset addtion. FM1 is 10mHz LPF in order to make the offset smooth.
- Add X_FINE and Y_FINE by the matrix.
- Control
- Turn off X_FINE out. Leave Y_FINE output turned on.
- Turn on ETMX ALS path.
- Servo setting: FM1 1000:30 ON, others OFF, gain1
- Wait for the beat comes in to the locking range at around 80MHz.
- If the peak is too far, sweep Y_FINE offset in order to . Or change GCV slow thermal offset to let the beat freq jump.
- You may have ambiguity of the feedback sign depending on which green has higher freq.
- After the capture of the ALS lock, increse the gain up to 20. Turn on 0.1:boost at FM3.
o Comparison of the stability of the beat freq (Attachment3)
- The spectra of the VCO PLL feedback was measured.
- First of all, the signal was measured without ALS (blue).
The PLL lost lock quite frequently, so the careful adjustment of the offset was necessary.Still I think there was slight saturation upconversion.
- Then, the ALS was turned on (red). The gain was 20. This is an in-loop evaluation of the servo. The suppression was ~1000 at 1Hz.
o Beat freq scanning
- The following command was used for the beat note scanning
ezcastep -- "C1:GCV-YARM_FINE_OFFSET" "5,500"
- Once the IR transmission was found, the scan was stopped.
- Because the resultant rms stability of the arm was not within the line width of the cavity, the smooth resonant curve was not obtained.
- From the shape of the error signal the peak-to-peak displacement (f>1Hz) was estimated to be +/-0.7nm. The dominant displacement
in the period is 16Hz component.
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