jenne.driggers@LIGO.ORG - posted 14:05, Wednesday 26 June 2019 - last comment - 14:59, Tuesday 02 July 2019(50209)
Identifying the 10.43 kHz mode
[Georgia, Jenne]
- In prep for the measurement, at around 11:50am local we turned on the ETMY bias with 9 V (a little less than the 9.5 V value that ETMX uses). There is a lot of low frequency noise added, so we're sat here for ~7 min in case the data is useful, but then we're trying the other sign of the bias. We don't think that we need lower noise for our measurement (exciting the mode with various ESD patterns on different optics) though, so it should be fine either way.
- Keita points out that maybe we should think about grounding the ETMY bias input, since we aren't using it at all for lock acquisition.
- We were working on exciting the mode (not succesful yet), but lost lock. I suspect the lockloss is unrelated to our work, since none of the PI modes were any higher than they had been the whole lock, our excitation hadn't changed in a long time,
and Robert had said that he was planning to do some laser vibrometer work requiring contact with some HEPI piers. So, I suspect that the lockloss was a combo of Robert's work andthe fact that we're in EQ mode. Robert and crew were still in the H2 part of the LVEA, hadn't gotten near HEPI piers yet. - Acquisition guardian change: PRMI_ASC_OFFLOADED now turns off the PRMI ASC filter banks that were in use, prior to our trying to acquire DRMI lock. It looked like we were still sending signals out to the optics after we had lost PRMI when the SRM came back into alignment, which probably didn't help DRMI acquisition (although it did catch by itself).
- We are going to excite this time in the damping filter for PI mode 24, since then our RMS monitor won't be directly contaminated by our excitation, and will just monitor the actual peak height. New channel: H1:SUS-PI_PROC_COMPUTE_MODE24_DAMP_EXC, with a narrow bandpass in the awggui.
- Previous channel: H1:SUS-PI_PROC_COMPUTE_MODE24_BP_EXC.
- Had also tried exciting using the OMC deacon infrastructure, but that's not really what we want to be using for this identification measurement. We'll re-look at that when we're ready to implement deacon alignment for the OMC.
- To be continued in a comment by Georgia....
Terra called the control room and helped me excite the mode by increasing the gain in the dampining filter for mode 24 (no excitation required). We excited the mode until the PI_ESD_DRIVER_OUT monitors were several thousand counts. Though as we increased the gain we saw some broadband noise around our mechanical modes.
We set the ESD output matrix in the butterfly configuration (diagonal quadrants out of phase) and managed to ring up the slightly-lower-frequency 10.428 kHz mode (see first attachment, red is with the mode rung up). We then switched to the drumhead configuration (diagonal quadrants in phase), and managed to ring up the same mode again. So as yet we have not distingushed which mode this really is.
They saw something similar at LLO, and looked at the downconverted transmon QPD signal to distinguish between the two modes. During the first round of excitations I had the TR_Y QPD input matrix in the drumhead configuration (all quadrants added together). For the second round of excitations we switched the matrix to a pringle-mode. I will need to look back at the data and see if we saw our down-converted excited mode in the QPD.
Second attachment is the broadband noise with the ETMY ESD bias on, as noted by Jenne above.
The beams on the TransMon QPDs are so off-center that it might be hard or not possible to identify the modes using them. On each QPD (A & B) the lowest light segment has about 20x less light on it than the highest light segment. I think you'll need to center the beams on the QPDs to use them as a diagnostic.
I had a look anyway, and only see the downconverted mode when the Transmon QPD input matrix is in the pringle configuration, suggesting that the 10.427 kHz mode is a flower mode of ETMY. (I'm not sure if this is using only one QPD or some combination of both, it's not obvious to me from the PI screen.)
We didn't manage to ring up the 10.4305 kHz mode with our ETMY excitations, perhaps it is on a different test mass?
The last plots in this thread could be misleading. Slawek has pointed out that the QPDs should see the second order optical mode, but the linewidth we saw was too narrow for this... Maybe some electronic cross-talk?