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AdV-COM (1/√f noise)
mwas - 21:57 Thursday 03 October 2024 (65254) Print this report
OMC scans with SR aligned and misaligned

Did several scans in CARM NULL 1F with SR aligned, and SR misaligned in TY to have the DCP ~200Hz.

Figure 1 shows the four scans made today (in two different locks). The two scans with SR aligned are in black and blue, and with SR misaligned are in green and red. Most of the HOM decrease in power with SR misaligned, as expected. An exception is the order 2 mode which remains roughly at constant power. There is also some modes between 0MHz and 50MHz in this figure which either change in power by a factor 10 or move in frequency. I don't know what these are, I will need to look in the data more carefully.

Details

Unlocking and relocking to CARM NULL 1F
16h11m20 UTC - OMC scan started (CARM_NULL_SCAN_ON)
unlocked when the temperature scan was going back down

Relocked to CARM NULL 1F
Adding an offset in SR TY
-233.5 urad - starting steady state
0.6 offset in SR_TY_SET to make a transition in alignment over a few minutes
-232 urad - ending steady state, maintained with SR_TY_SET ~ 0.15
17h04m33 UTC - OMC scan started
17:26 UTC - stopping scan (CARM_NULL_SCAN_OFF)

Adding -16.0 MICH_SET to balance 56MHz sibeand on B1p

17h33m19 UTC - OMC scan started
17:54 UTC - stopping scan

Realigning SR and adjusting MICH offset to balance 56MHz sidebandon B1p

18h05m14 UTC - OMC scan started

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mwas - 13:45 Friday 04 October 2024 (65260) Print this report

A bit more analysis concerning the OMC scans, the first (blue) and last (black) measurement are with SR aligned. And with SR misaligned (green and red)

Figure 1. Shows highlighted the 56MHz sideband TEM00 and order 1 mode, both for lower and upper sideband. In addition the order 1 (~74MHz) and order 2 (~142MHz) of the carrier are shown. What is clear is that with SR misaligned the power of the 56MHz order 1 mode increase by a factor at least 5, which sounds reasonable. This explains the appearance of a peak around 20MHz in the FSR.

Figure 2 Shows the carrier modes from 1 to 12 from left to right. The peaks at ~45MHz that disappear with SR misaligned is the order 12 mode of the carrier. The HOM powers look reduced in power by at least a factor 2, and up to a factor 10 (for mode 4). The order 2 modes look all with similar power.

We can actually have 4 measurement of the order mode power in a single scan, two crossed when the OMC temperature is increasing and two when it is decreasing. This is not the case for the first (blue) measurement, as the interferometer unlocked during the down going scan.

Figure 3 shows all the measurents, there is lots of scatter with a single configuration having factor ~2 changes. So the order 2 mode is constant versus SR misalignement, but the error bars of that statement are that is constant within an error band of a factor 2.

/users/mwas/OMC/OMC_scan_demod_20241003/OMC_SCAN.m

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