I processed some bandlimited intensity noise injections I did on August 18 of this year.
The goal was to resolve the low-frequency intensity noise projection to DARM.
This is a difficult business because the intensity loop works strongly suppresses low frequency noise, and easily saturates when you inject a high levels to see the noise in DARM.
In our case, we've seen that increasing the intensity injection amplitude actually reduces the coherence seen, since nonlinear noise rises faster with higher intensity RMS.
So to reduce RMS, I made some fine bandlimited injections, saved in the same place as alog 52864.
The results are strange, quite unlike our intensity to DARM results from O3.
See plot 1 for the TF in m/RIN, plot 2 for the DARM projection in m/rtHz.
First, the total coupling is far lower now than in the past at LF, see alog 52864.
At HF, it's about the same.
Second, there is some unexpected dips between 20 and 30 Hz. I sort of expected this region to be dominated by differential radiation pressure due to arm power differences dP_arms
.
Third, there is a clear dip at 70 Hz, and a corresponding phase flip from around -45 to 45 degs.
We saw something similar to this in the past, as we switch from radiation pressure to contrast defect intensity coupling.
(There is a sign difference between these plots and alog 52864.
I believe the signs in this alog are correct.)
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Full data for these plots is in: /ligo/home/craig.cahillane/Git/IFO/IntensityNoise/data/Injections/20220818
Scripts for generating these plots in: /ligo/home/craig.cahillane/Git/IFO/general/scripts
Terminal calls were:
To process data (in labutils env):
python run_all_intensity_noise_injection_plots.py /ligo/home/craig.cahillane/Git/IFO/IntensityNoise/data/Injections/20220818/Intensity_inj_*.hdf5 1344821693 1344831693 -o 0.5
To stitch TFs (in psl env):
python /ligo/gitcommon/psl_measurements/code/multi_tf_plot.py *intensity_to_darm_tf.txt --stitch -u --title "Stitched bandlimited intensity to DARM injections - August 18 2022" -y log -s --labels "100-200 Hz" "2000-7000 Hz" "200-300 Hz" "20-30 Hz" "300-2000 Hz" "30-40 Hz" "40-60 Hz" "60-100 Hz" --legend_loc outside -y1 1e-14 -y2 1e-11 --units "m/RIN"
To stitch ASDs (in psl env):
python /ligo/gitcommon/psl_measurements/code/multi_spec_plot.py *intensity_to_darm_asd_projection.txt --stitch --title "Stitched bandlimited intensity to DARM injections - August 18 2022" -s -x1 10 -x2 7500 -y1 1e-23 -y2 1e-16 --ylabel "DARM [m/rtHz]" --labels "100-200 Hz" "2000-7000 Hz" "200-300 Hz" "20-30 Hz" "300-2000 Hz" "30-40 Hz" "40-60 Hz" "60-100 Hz"