Reports until 15:38, Monday 14 January 2019
H1 ISC (IOO, PSL)
sheila.dwyer@LIGO.ORG - posted 15:38, Monday 14 January 2019 - last comment - 17:07, Monday 14 January 2019(46404)
Intensity noise from second loop limiting DARM at 25 Hz, as well as 350-400 Hz

As Danny reported on Friday 46382, the HAM2 motion coupling to DARM that Robert noticed 46373 is coupling through the ISS second loop, and there is also strong coherence with DARM below 30Hz.  

Dany and I used data from several different locks on Friday, and we couldn't make a good comparison of the low frequency noise in DARM because some of those locks had large scattering or other low frequency problems. This morning Keita Jenne and I got about 10 minutes of data with the ISS second loop in 4 different states while the interferometer was in low noise:

second loop off, output switch on Jan 14th 2019 18:38 UTC
second loop off, output switch off 18:48 UTC
2nd loop AC coupled 18:59:30 UTC
2nd loop DC coupled 19:17 UTC

The attached DARM spectrum shows that the ISS was adding noise to DARM both at 25Hz and below and from 350-400Hz.  The coherence  of the ISS out of loop diodes with DARM is pretty much the same weather the second loop is AC or DC coupled.  REFL RIN also indicates that the intensity noise imposed by the second loop is the same for the AC coupled or DC coupled ISS.

Georgia and Danny have pico'd the array to fix this. 

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georgia.mansell@LIGO.ORG - 17:07, Monday 14 January 2019 (46412)

We pico'd onto the ISS second loop QPD and PD arrays. We have improved the RIN on both the inner (in-loop) and outer (out-of-loop) PD arrays (first attachment), and the alignment onto the individual photodiodes and the QPD (second attachment).

Gabriele last centred the beam on the array last year. There are two picomotor mirrors on the path from IM4 to the ISS arrays, we adjusted both PM1 and PM5, but mostly PM1. We did this pico'ing with the IFO unlocked, and the power through the mode cleaner at 30W.

We definitively made the noise better from 300 Hz - 1 kHz, though we noted the peaks around 485 Hz seemed to be breathing a bit. We also noted the 60Hz line appears worse on the inner PDs than the outer, perhaps we could consider switching which is the in-loop sensor.

The second attachment shows time series' while picoing. The first row is the PDs and PD sums for the inner sensor, the second row is for the outer sensor, and the third row is the QPD. The final colum is the picomotor positions, at t = -750 we switched between the picomotors.

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