The CBC data quality group have been looking at the noise coming out of the PSL to practice detector characterization for aLIGO. We noticed that there is a significant change in the nature of the PSL spectrum between Jan 29 and Jan 30, 2013, possibly correlated to the PSL reboot. I have attached plots of spectrum of H1:PSL-ISS_PDA_OUT_DQ to show this. The first plot (viewer-0.png) shows the PSL spectrum from a good time on Jan 29. I have also attached the status of the PSL online detchar channel (ODC) for the same time period (viewer-1.png). The ODC state is all green, indicating that the PSL is functioning correctly and both the ISS and FSS are locked. This spectrum looks good. However, the PSL spectrum from this morning (Jan 30) appears to have a strong line at 60 Hz with a harmonic at 120 Hz, a new line at 300 Hz, a forest of lines above 500 Hz, and a large bump at 650 Hz (viewer-2.png). I looked at the ODC data to pick 60 seconds where the PSL is locked to make the spectrum (viewer-3.png). The PSL appears to be going in and out of lock much more today. I tried picking a time this morning when the PSL was in a good state for a longer period of time. I have attached the PSL ODC plot for 40 mins from 0800 PST (viewer-5.png) which shows that there appears to be a good stretch of data at 0828 PST. The PSD for this time (viewer-4.png) does not have the large bump at 650 Hz, but the other lines are still there. Is this a known issue with the PSL?
Michael asked if there was any difference in the IMC lock state between these two times. I made plots of H1:IMC-MC2_TRANS_SUM_OUT_DQ minute trends for 40 mins starting Jan 29 0800 PST and Jan 30 0800 PST (attached). It looks like the IMC was unlocked during both these times (at least I don't see any steady periods in the level of the transmitted light).
I created a current ISS spectrum along with an RPN plot of the laser using the DBB. The RPN measurement looks the same as it did last time I took it, so I don't think it's the laser. I switched PDs in the ISS loop and tried adjusting the gain but the noise is still there. I did find the noise eater off on the NPRO, but there was still no difference when I turned it on (I've left it on).
Duncan, the QPD in trasmission of MC2 was not cabled as of Jan 30th (they are working on it right now), so H1:IMC-MC2_TRANS_SUM_OUT_DQ will not show you anything reasonable.
Instead, if you want o track the lock status of the IMC, I suggest you look at H1:IMC-REFL_DC_OUT_DQ. With the current operating powers, it will show you something around 450 counts when the IMC is unlocked, and something in the ~100 range (60-130 depending on the alignment into the IMC, lower means better).
Following Giacomo's suggestion, here are the MC REFL plots for Jan 29 and Jan 30 around the time I took the PSL spectra. These show that the first (clean, line free) spectrum on Jan 29 at 0800 PST was taken from a time when the IMC was locked, but the second two were not. I took another spectrum on Jan 30 at 8:22 PST when the IMC was locked and it still shows the forest of lines. Bottom line: this extra noise in the PSL ISS PDA spectrum seems to have appeared sometime between Jan 29 and Jan 30. It is there when the IMC is locked. This may all just be due to looking at PSL data while IMC commissioning is going on, but it might be worth following up to see if something changed in the IMC/PSL coupling between Jan 29 and 30.
