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AdV-ISC (Commissioning up to first full interferometer lock)
flaminio - 0:40 Friday 03 December 2021 (54086) Print this report
A few observations about two recent locks (30/11 and 01/12)
The two plots attached to this elog entry are the ones that I showed at the meeting earlier today.

The first shows some of the interesting signal during the 25' long lock on 30/11.
- In the middle of the lock the SR mirror alignment in TY has been changed. As already noticed this reduces the B1p_DC and increases B7_DC/B8_DC.
Moreover the increasing trend in B1p_DC is stopped. At the same time there is a decrease in the overlap of carrier and LSB as measured by the phase camera on B4.
- During this lock SPRB is kept aligned using the centering of the 112 MHz signal on QD2 (top right plot). In order to do so the bench is moved in TX and the same motion is visible on the QD2 DC V i.e. the carrier beam in vertical. This confirms that the carrier and the sidebands are moving differently and that the sidebands are moving more than the carrier (at least vertically). The relation between the motion in the bench in TY and the QD2 in the horizontal direction is less obvious and it seems to change slope when the SR mirror is moved (also in TY).

The second plot shows the sidebands (56 and 6 MHz) and the carrier during the long lock on 01/12.
- While all four sidebands look pretty much superposed, the carrier is slightly shifted in position (and also rotated). If one looks at their motion as a function of time the sidebands seems to "dance" coherently while the carrier is on a different rhythm (a slower one).

Images attached to this report
Comments to this report:
bonnand - 10:01 Friday 03 December 2021 (54090) Print this report

If you want to see the "dance" of the sidebands and carrier of B4 beam, here is a video of the B4 phase camera images around the moment where SR_Ty was moved horizontally during the lock of the 30/11.

SR_Ty was moved at 16:40:37 UTC (1min2sec in the video), it has hard to see if the beams moved with SR.

I would advise to watch the video in accelerate.

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