Ansel and Sheila following up on 77990. This work relates to the 9.5 Hz comb triplet .
Channels involved
- H1:PSL-ISS_PDA_REL_OUT_DQ - identified as a possible witness in 77990, which started the rest of the investigation. Does not see the 9.5 Hz combs when the ISS second loop is off.
- H1:PSL-ISS_PDB_REL_OUT_DQ - does see the 9.5 Hz combs (very clearly!) even when the ISS second loop is off, and even when the IMC is unlocked. Selected as best channel for tracking the time dependence of the comb (below).
- Other places the combs are seen, albeit not as clearly:
- H1:PSL-PMC_HV_MON_OUT_DQ - also identified as a possible witness in 77990, combs are present here but much weaker.
- H1:PSL-ISS_SECONDLOOP_PDSUMOUTER_OUT_DQ
- H1:PSL-ISS_SECONDLOOP_PDSUMINNER_OUT_DQ
- H1:PSL-PWR_NPRO_OUT_DQ (laser power before amplifier)
- H1:PSL-PWR_HPL_DC_OUT_DQ (laser power after amplifier)
(Thanks to Sheila for guidance on channels and times here!)
Comb history
With this information in hand, it was possible to track the 9.5 Hz combs back to a likely start date on or near Sept 2, 2021. Details:
- I used the PDB channel first to determine that the combs appeared between August 30 and Sept 7, 2021. After that I switched over to some of the channels where the comb is more faint (H1:PSL-PMC_HV_MON_OUT_DQ, H1:PSL-PWR_NPRO_OUT_DQ, H1:PSL-PWR_HPL_DC_OUT_DQ), as there wasn't any good data from PDB (presumably due to the ongoing work), and found a distinct change point between the Sept 1 and Sept 2 daily spectra. A spreadsheet showing the dates & channels checked is attached.
Checking the alogs around that time, there was quite a bit of PSL upgrade work ongoing, as summarized in 59832.
This work is ongoing; as before, details and work-in-progress notes can be found on gitlab. Anamaria and Matt H have supplied a number of times to look at LLO data (recall that these combs have counterparts at LLO), particularly for dark spectra of the ISS PDs. This is next on the to-do list.
What about the 11.9 Hz comb mentioned in the previous alog?
It's also in a lot of these channels! However, unlike the 9.5 Hz, I don't see a notable change point in early September. This is not really surprising, since the 11.9 Hz comb was noted in O3. I'm focusing on the 9.5 Hz combs first, which are more pervasive, but keeping an eye out for more 11.9 Hz clues along the way.
Anybody interested in looking at the spectra can find the full set of plots here (more will be added as I work): https://ldas-jobs.ligo-wa.caltech.edu/~ansel.neunzert/iss_channels_combs/ .
