After aligning the IR to both arms, we did a arm finesse ring-down measurement. The fit uses the nominal ITM transmissions (0.44% ITMX, 0.48% ITMY).
X-arm:
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Finesse = 1399
Power build-up factor = 891
Ring-down half-life = 3.11msec
REFL POWER locked/unlocked = 0.96
Y-arm:
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Finesse = 28
Power build-up factor = 18
Ring-down half-life = 0.42msec
REFL POWER locked/unlocked = 0.50 (agrees with experiment)
We also tried to move the alignment of the y-arm around a bit, in the hope that we could find a better spot. There was only very little dependence on spot position.
Finally, we also did a beam scan of the y-arm, confirming a 30-ish finesse. That picture is also attached. Note the wide, almost double-peaked resonance structure.
Attached are plots of the ring-down data (blue) and fit (orange), as well as the plotting function and raw data.
[Masayuki, Yutaro]
This is the result of cavity scan of Y arm for green.
From this, finess is estimated to be 17, while the design is something like 50.
[yutaro, masayuki]
The attached picture is four resonant peaks with free swinging cavity. I picked at random, and they don't seem to have double peaks.
Attached plot is long term trend of the IR (right) and GR (left) transmitted power with the the temperature of ETMY (upper). The transmitted IR power was around 3000 and the GR power was 1500 about one month ago, and seems to get smaller with the ETMY temperature.
Mmm, does it indicate anything?
[Keiko, Takaaki, Stefan, Masayuki]
The ETMY started to be warmed up today. We did ring-down measurement again, and found that the finesse got increased even at 33 K. The estimated finesse is 120, corresponds to the mirror loss of 1.1 %. We did several measurement and all of the fittings shows consistent value.
The low finesse might be because of the contamination on the mirror...??
Here are the fitting results of three ring-down measurement when 33K on Friday:
- GPS 1242116740 Finesse 121
- GPS 1242116820 Finesse 129
- GPS 1242116800 Finesse124
Stefan's simple fitting script was used.
