Fabian, Washimi, Yokozawa

We started the investigation of the vibration noise at the SR3 chamber.

First motivation is that there is large coherence between MICH displacement and SR3 opvel pitch and yaw.

We want to distiguish the SR3 suspension is really flactuating or optical lever pick up the environmental vibration.

The detail report and analysis will be reported by Fabian, I quickly checked the measured data.

Fig.1 : Spectrum and coherence between SR3 oplev pitch and accelerometer which was placed under the oplev receiver table

There is some coherence above 40Hz, but not in 17Hz and 35Hz. But there is very large 60Hz noise I suspect that ground loop was happened. I need check the ground issue tomorrow

Fig. 2 : Spectrum and coherence between SR3 oplev pitch and accelerometer which was placed under the oplev transmittance table

There is quite large coherence at the 17Hz and 35Hz. And shape of the spectrum is consisitent. From this result, at least oplev transmittance part pick up the vibration and detected at the QPD.

Fig. 3 : Spectrum and coherence between SR3 oplev pitch and accelerometer which was placed the SR3 outer frame.

Similar to the Fig.2. case.

Fig.4. : Spectrum and coherence between accelerometer which was placed under the oplev transmittance table and which was placed at hte SR3 outer frame

most peak above 10Hz is comes from the vibration of the SR3 frame.

(Current SR oplevs above the 10Hz  are good accelerometers)