fibre_walk_project_code/fitting_ringdown.org

Fitting Ringdown

• Fitting transients
• Failure of the steady state
• Weird Oscillations

Fitting transients

• one can solve the equation of motion for when a mode is in the steady state and the laser is suddenly switched. one obtains a decaying oscillation which can be fitted to the data.
• this works ok, when the system was in the steady state before the jump
• see /hiro/fibre_walk_project_code/src/commit/5cda9758f4c30ed574d389368485bb83c7ac3038/scripts/transients_without_amplification.py
• we obtain \(γ\approx\SI{2.2}{\kilo\hertz}\) but this can vary a lot
• the detuning frequency seems to be completely off

Failure of the steady state

On the right peak on can see that there might be something fish going on. This is data/24_05_24/nice_transient2.

Weird Oscillations   ATTACH

• when turning on the amp while the laser is running we get some oscillations at \(\sim \SI{40}{\kilo\hertz}\) which is a period of \(\SI{25}{\micro\second}\). this is 500 times roundrip time :(). I thought it might be a wave packet traveling around the loop, i.e multiple modes together…

osci_closeup.png osci_far.png cleaned.png

• it isn't close to the fsr though…
• fitting a sine to that gives pretty much the same, as does an fft cleaned_fit.png
• it is pretty constant over all steps in data as can be ascertained from this script
• these are also present w/o the amp cutout!

osci_without.png