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fabian.arellano - 16:44 Tuesday 30 July 2019 (9703) Print this report
Residual motion of the optic in ALIGNED and FLOAT states

Today I measured the residual motion of the optic in ALIGNED and FLOAT states.

In both states the optic RMS displacment and velocity fulfills the requirement, which suggests that turning the control system off for the payload during observation time should be fine if considered necessary. It's worth mentioning the main interferometer team wants to have some sort of local control system for the payload during observation time, but the details still have to be decided.

This table shows the integrated RMS displacement for each degree of freedom and the requirement.

Degree of freedom ALIGNED FLOAT Requirement
Longitudinal displacement 0.25 µm  0.3 µm 0.4 µm
Longitudinal velocity 0.3 µm/s 0.3 µm/s 0.5 µm/s
Pitch displacement 0.17 µrad 0.15 µrad 1 µrad
Yaw displacement 0.42 µrad 0.35 µrad 1 µrad


  • There is no inertial damping.
  • Directory: /kagra/Dropbox/Subsystems/VIS/TypeBData/SR2/Noise/Measurements/20190730/
  • File for ALIGNED state: SR2_ALIGNED_TM_OPLEV_ASD_190730_1564468105.xml
  • File for FLOAT state: SR2_FLOAT_TM_OPLEV_ASD_190730_1564469006.xml
  • Bandwidth of the displacement measurement' from 0.010 Hz to 800 Hz.
  • The bandwidth of the optic velocity measurement was from 0.010 Hz to 10 Hz. Above 10 Hz there is a lot of noise which I don't believe is real displacement of the optic. The peaks are likely related to the oplev optics support platform
  • Related entries: 8945, 9456., 9697, 9702.
Comments to this report:
fabian.arellano - 15:04 Thursday 01 August 2019 (9752) Print this report

In case you don't see the plots attached to this report please click here: 9752.

This report shows the amplitude spectral densities of those degrees of freedom whose integrated RMS is larger or equal in ALIGNED state than in FLOAT state. Namaley, pitch, yaw and longitudinal velocity. See figures 1, 2 and 3 respectively.

We can see that in pitch and yaw the control system seems to be introducing an unsuitable amount of noise in the following frequency bands:

  • Pitch: 0.380 Hz and  2 Hz.
  • Yaw:  0.045 Hz and 0.230 Hz.

In the case of the longitudinal speed the control system seems to excite a large peak at 0.705 Hz.


If you won't ever need to work with data similar to the one used in this report, you likely don't need to read this section.

  • I exported the longitudinal velocity from diaggui using the channel name win1_pad0_trace0.
  • Directory: the same as the data files.
  • File names: SR2_FLOAT_TM_OPLEV.txt, SR2_ALIGNED_TM_OPLEV.txt, FLOAT_ALIGNED_TM_comparison.m.
  • The text files have six coulumns each: frequency, pitch, yaw, pitch RMS, yaw RMS, longitudinal velocity.
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