First attempt failed.
- First input/output matrix was put in place by Jax.
- WFS demod dark offset was set.
-
Briefly closed the servo and things didn't make sense.
- WFSA error was zeroed but WFSB not. Cavity was apparently misaligned.
- Even without the servo, I couldn't flip the sign of WFSB error by tilting ETM and/or ITM.
OL whitening.
See Thomas's entry. ITMX and ETMX are good now.
Demod phase and sensing nonsense.
After Thomas was done with OL, we had to measure sensing matrix again as it uses OL data. Found that demod phase changed, not reliable from measurement to measurement. In the end, I've found that:
- WFS demod phase and the sensing matrix is highly dependent on the cavity alignment or the WFS centering or both.
-
I needed to align the cavity by hand really well and center the WFS to obtain a reliable demod phase.
- Even then, it looked as if the amplitude of sensing matrix elements varied by maybe a factor of 1.5 or more over 10 minutes time.
- WFSB beam position moves more than WFSA.
The measurement was done by wiggling ETMX at 3.5Hz and ITMX at 1Hz, first in YAW, measuring the demod phase and the sensing matrix for segment 1 and 3, then switch to PIT for 2 and 4. Angle to length shouldn't be a problem as PDH should have a large gain there to squash the length error.
New sensing matrix.
The attached shows one snapshot of demod phase itself on the left screen and the demod phase/sensing matrix measurement on the right.
Two dtt sessions show PIT and YAW. In each dtt window, left is ITM and right is ETM, top shows how Q phase is minimized, middle shows the sensing matrix amplitude in cts/urad (WFS/oplev), bottom shows the sensing matrix phase (should be 0 or +-180) as well as relative phase between diagonal elements (should be +-180).
The sensing matrix phsae still has 10 deg-ish systematic at 1Hz (ITM) and 25 deg-ish at 3.5Hz (ETM). Maybe a decimation filter for OL DQ, maybe something else, definitely not 1:10 whitening, I don't worry about this for now.
PIT.
| ITM | ETM | |
| WFSA | -1922.46 | -1651.43 |
| WFSB | -655.52 | -393.65 |
YAW.
| ITM | ETM | |
| WFSA | -3243.17 | 1042.83 |
| WFSB | -2947.28 | 931.62 |
That was it for Friday. I will not work over the weekend at the site.
Corresponding input matrices:
Pitch:
| Hard | Soft | |
| A | -0.000568 | 0.000588 |
| B | -0.00228 | 0.00776 |
Yaw:
| Hard | Soft | |
| A | 0.0526 | -0.0582 |
| B | -0.0274 | 0.0299 |
These have been updated accordingly.
I've also attached a matlab script that will turn the sensing matrices into input matrices, just to make sure the method exists somewhere other than my notebook.
