Reports 1-1 of 1 Clear search Modify search
AdV-DET (Output mode cleaner)
mwas - 16:30 Wednesday 22 March 2017 (36980) Print this report
OMC short scan on dark fringe
This morning piggy-backing on locking operations did two quick scans of the OMC1.

Figure 1, scan on recombined ITF at half fringe, the top middle pannel shows that the TEM00 mode is at 15mW, and TEM10 is at 1mW. We managed to have 0.5mW on the TEM10 before, so the alignment could be better but is decent.

Figure 2, shows 3 peaks with ITF on dark fringe (see figure 3) and the OMC1 temperature changing (not linearly). The first peak (0.6mW) is a TEM00, the second (3mW) is a TEM00, the third peak (9mW, off scale on the figure) is a TEM10. The mode of different orders are separated by ~70MHz for the OMC. So the brighter TEM00 should be the 56MHz side band, and the bright TEM10 is the first order mode of the 56MHz. The smaller TEM00 is either the carrier or the 6MHz, I would expect it to be the carrier as only a single peak is visible.

For science mode we plan to have ~80mW going through the OMC. B1s2 sees 8% of the light, so that would correspond to 6.4mW. So the amount of carrier TEM00 available in this scan of the OMC is 10 times smaller than what we would like to have in the end. Having some dark fringe offset, would make it easier to lock the OMC and confirm that the currently first TEM00 in the scan is indeed the carrier one.
Images attached to this report
Comments to this report:
mwas - 15:01 Thursday 23 March 2017 (37005) Print this report
Today, mid-day, I have made a larger range, slower scan of the OMC with the ITF at dark fringe.

Figure 1 shows the scan (in the opposite direction than previously), looking at the camera at the same time, I have noted the shape of the modes going through the OMC.
Found only two TEM00 modes (expected 3: carrier, lower side-band, upper sideband), that would mean that the upper side-band TEM00 is hiding underneath the carrier TEM10 mode, which would be 10 times brighter.
Hence the small a clean TEM00 is the lower side-band, and the brighter and jagged TEM00 is the carrier (contrary to what I have said in the previous entry).

It actually is not surprising for the carrier TEM00 to be jagged. The loop is on dark fringe, so we just see here the noise of the loop fluctuating around the proper dark fringe. This means that we could try to lock the OMC without a dark fringe offset, as there is substantial offset already (contrast defect?). But of course having some controlled dark fringe offset would make it easier and presumably lower the power fluctuations.
Images attached to this comment
Search Help
×

Warning

×