Cascina, June 19th, Brewster window noise ? Raffaele Flaminio EGO and CNRS/LAPP Summary - Original observations - Brewster window replacement - New problems - Solutions - Conclusions?

Cascina, June 19th, Scattered light noise Environmental noise acting on in air components + Scattered light from in air components = Phase noise in the interferometer (with the typical environmental-like noise structures) Laser Brewsters End benches Detection bench Injection bench

Cascina, June 19th, Brewster windows Brewster windows separating different vacuum regions Laser Brewsters End benches Detection bench Injection bench

Cascina, June 19th, DETECTION BENCH DETECTION BREWSTER DN250CF

Cascina, June 19th, IB PR Al BAFFLEGLASS BAFFLE INJECTION BREWSTER

Cascina, June 19th, Acoustic noise entering from the Brewster (“Radio Brewster”) - Several test and studies made by Irene Fiori - Predictions “strange”; expected ITF noise larger than measured ITF noise (and coherence with Brewster seismometer pretty bad) - Explication: maybe seismometer not measuring the good surface Original observations Brewster replaced with a larger one - From 16 cm diameter to 19.6 cm diameter

Cascina, June 19th, 20077

8

9 With new Brewster ITF noise worst than before New Observations (I)

Cascina, June 19th, With new Brewster ITF noise worst than before Foreword (II)

Cascina, June 19th, Coherence with Brewster seismometer better than before New observations (II)

Cascina, June 19th, With new larger Brewster new light visible on the detection bench - Light visible at ~10 cm from the axis of the main beam - This light is missing the first detection lens (L1, diameter 12 cm) - This light is diffused on a couple of supports on the detection bench New observations (III) B1s B1 B1p B5 L3 /2 OMC M1 M5 L7

Cascina, June 19th, Julien Marque (2004) Old prediction: spurious beams Bd1 Bi2Bi1 Bd2

Cascina, June 19th, Julien Marque (2004) Old prediction: spurious beams Bd1 Bd2

Cascina, June 19th, Julien Marque (2004) Old prediction: spurious beams Bd3 Bd4 Bi1

Cascina, June 19th, Julien Marque (2004) Old prediction: spurious beams Bd3 and 4

Cascina, June 19th, Julien Marque (2004) Old prediction: spurious beams Bd5 Bd6 and 7 Bd8 Bi2

Cascina, June 19th, Julien Marque (2004) Old prediction: spurious beams Bd5 Bd7 and 8 Bd6

Cascina, June 19th, With the old brewster One of the predicted spurious beams Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam

Cascina, June 19th, With the new brewster One of the predicted spurious beams Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam

Cascina, June 19th, With the new brewster Considering beam diameter defined as 2 w 0 One of the predicted spurious beams Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam

Cascina, June 19th, A possible scenario: - “Brewster noise” due to spurious beams - Scattering from the Brewster link lateral wall into the B1 beam Another discussed scenario: - More spurious beams reaching the detection bench - Then scattered into B1 - Difficulty: bench is suspended in vacuum, no direct coupling with environmental noise Another possible scenario: - More spurious beams reaching the detection bench - Then scattered on the tower wall or on the Brewster - Then scattered back into B1 Discussion

Cascina, June 19th, Additional diaphragm before the Brewster A possible mitigation Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam

Cascina, June 19th, Additional diaphragm before the Brewster Other predicted beams - more uncertain - less powerful A possible mitigation Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam

Cascina, June 19th, Additional diaphragm before the Brewster Considering full BS aperture A possible mitigation Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm)

Cascina, June 19th, Scattering of spurious light from the ITF ? Yes, but …. …… no difference in the ITF noise

Cascina, June 19th, Noise injections (May 2 nd )

Cascina, June 19th, Injection with shaker: comparison with old Brewster Noise injections (May 2 nd )

Cascina, June 19th, Injection with loudspeaker: comparison with old Brewster Noise injections (May 2 nd )

Cascina, June 19th, Damping the Brewster

Cascina, June 19th, ITF noise: ‘damped’ Brewster

Cascina, June 19th, ITF noise:‘damped’ Brewster

Cascina, June 19th, Noise projection I. Fiori and G. Vajente

Cascina, June 19th, Discussion ITF noise larger because of new Brewster Brewster link vibrating more than before? No. Sensitivity to Brewster vibrations larger than before? Yes Why? What is the mechanisms ? BEAM SPLITTER DETECTION 1) Scattering of spurious light coming from the ITF 2) Scattering of spurious light generated in the Brewster 3) Scattering of spurious light coming from the detection

Cascina, June 19th, Scattering of spurious light generated in the Brewster Possible but new Brewster is expected to be better - larger Brewster window - larger exit windows - Brewster window with larger roughness? No (source: L. Pinard) - Brewster window with larger residual reflection? with mW incident ~ 270 mW reflected 200 mW on P pol and 70 mW on S-pol (source: P. La Penna) - Brewster link vibrating more? No. - Something in the Brewster vibrating more? Candidate: aluminum baffle

Cascina, June 19th, Scattering of spurious light coming from the detection BEAM SPLITTER DETECTION 3) Scattering of spurious light coming from the detection Decision to better protect the Brewster from light coming from the detection side

Cascina, June 19th, Conclusion

Cascina, June 19th, Conclusion

Cascina, June 19th, Injection with shaker: comparison with old Brewster Noise injections (May 9 th )

Cascina, June 19th, Injection with loudspeaker: comparison with old Brewster Noise injections (May 9 th )

Cascina, June 19th, Identification of 122 Hz with one of the Brewster link supporting legs Change of Brewster link damping configuration Change of SR pump with a smaller one More investigations (I)

Cascina, June 19th, Clear excitation of 136 Hz and 241 Hz tapping on DT east flange Damping on DT east tube Large effect on ITF sensitivity when tapping on DT west flange Damping on DT west tube No effect on sensitivity More investigations (II)

Cascina, June 19th, Observation of diffused light coming from detection output window Cleaning of window No effect on sensitivity More investigations (III)

Cascina, June 19th, Tapping tests on injection Brewster, injection tower, injection table - Small effects on ITF sensitivity - No excitation of ITF noise structures/resonances - Much less sensitive than detection tower and Brewster Tapping tests on injection Brewster, injection tower, injection table - Very small effects on ITF sensitivity - No excitation of ITF noise structures/resonances Tapping test attempted on NI - failed due to unlock Need to study sensitivity to all towers vibration - need to learn how to excite towers without unlock - place seismometers in more useful positions (now measuring vertical seismic noise near tower base) More investigations (IV)

Cascina, June 19th, Result

Cascina, June 19th, Conclusion - The new Brewster was limiting the sensitivity - The sensitivity is back to what it was on April the 6 th (before the Brewster was changed) - Sensitivity to environmental noise still there - No big improvement with new Brewster (why?) - Tapping test and injections continue to tell that the detection tower and the Brewster are the most sensitive parts of the ITF (but several tests still to be done) - How to make the difference between the tower and the Brewster?

Cascina, June 19th, Result

Cascina, June 19th, “Mystery noise”

Cascina, June 19th, “Mystery noise”

Cascina, June 19th, “Mystery noise”

Cascina, June 19th, “Mystery noise”