1 - the ITF unlocked due to the earthquake
2 - the RFC also unlocked after a while and re-locked from time to time, but not stably enough
3 - during this period, AlpInj continued executing the macro that keeps MC_zCorr close to zero by moving the MC IP y offset. This macro is disabled when the RFC is unlocked. However, it acted many times during the earthquake period and always moved the IP in the same direction. At the end the MC was moved from 3075 to 3421, meaning a displacement of about 378 um.
4 - the laser frequency was forced to follow, since the IMC remained mostly locked. Master laser thermal correction increased up to 6 V. The relative IMC lenght change was about 2.6e-6 which would correspond to about 800 MHz of laser frequency if the IMC was always locked. Indeed the IMC remained locked during some of the MC IP ramps: during this periods the laser frequency followed.
5 - Finally the RFC relocked, after the earthquake calmed down. The IMC was longer and the master laser thermal correction larger.
6 - Step 1 was requested and ResetFmodErr executed. The master laser thermal correction was reset to zero. When the IMC relocked, the RFC relock moved the thermal correction to -0.6.
7 - FmodErr continued moving the MC IP back to the initial position to compensate for the wrong FmodErr.
8 - Finally the IMC relocked with the same length as at the beginning, but with different master laser thermal correction. A final adjustment of modulation frequency brought it back to the initial value.
At the end the IMC has the same length as before, but the master laser frequency was different, since the RFC unlocked during the transient.
As already reported, the OMC changed its working temperature, emaning that the laser frequency was changed. The change in temperature was of 0.18 degrees. The full temperature scan between two different resonances was visible shortly after: 1.60 degrees. Therefore the frequency change was 0.11 OMC FSR. This corresponds to a laser frequency shift of 460 MHz, considering the OMC length from the Optical measurements page.
According again to the Optical measurements page the RFC FSR is 470 MHz, which matches quite well. We can conclude that the accident induced a jump to the next fringe of the RFC.
As a side effect, we can calibrate the master laser thermal correction: 280 MHz / V.
