To complete these observations:
Finesse has been measured on thursday, right after cleaning the cavity with ethanol @6000.
Finesse has been measured on friday, after opening the cavity for few tens of minutes @12000-12500. The cavity was openned while locking and the transmission was continuously and ~linearly increasing.
Finesse has been measured today after ~50h pumping with primary vacuum @17000. It's back to the highest value we've ever measured on this cavity.
Parameters @17000 finesse:
Input power: 7.85 mW (Koheras + AOM + 2*EOM)
Coupling: 70-75% => Pin ~ 5.9 mW
Transmission through S2 and P4: 50 µW (transmission estimated to 1.5 ppm) => Pcav ~ 33 W => G ~ 5600
It is compatible with a simulation with nominal parameters for mirrors and adding 47ppm by mirror of losses (absorption and scattering) which indicates 17k of Finesse and 4100 of power gain.
in this simulation, the coupling should be 94% instead of the 70-75% measured. It is possible that the losses (47 ppm) are not the same on all mirrors.
| Ronic Chiche wrote: |
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After mirrors were going back from LMA for cleaning and thermal anealing, they have been installed in FP cavity for Finesse measurement.
after getting strange results when the cavity is closed (very low Finesse...maybe too much ethanol inside cavity procucing some lineic losses), we get 12k-12k5 Finesse with primary vacuum (~4 mbar) and a clean lock (very flat transmission signal and quite noiseless reflection signal)
we let the cavity pumped all the WE to see if we can measure a difference or not at lower pressure.
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