Gabriele Vajente ILIAS WG1 meeting - Perugia Couplings of angular noises into dark fringe Diffused light studies

ILIAS WG1 meeting – Gabriele Vajente2 Summary Non-stationary noise couplings due to input beam jitter Preliminary study of daily trends Preliminary projections of angular control noise Acoustic noise by diffused light

ILIAS WG1 meeting – Gabriele Vajente3 Non stationary noises

ILIAS WG1 meeting – Gabriele Vajente4 Input beam jitter Temperature fluctuations in Laser Lab causing input beam jitter Powers oscillates with 20 min period Does this input beam jitter couple into high frequency noise? Search for modulated noises analyzing long locks (up to 40 h) IMC transmission and PRC pick-off powersIMC end quadrants diodes

ILIAS WG1 meeting – Gabriele Vajente5 Input beam jitter Temperature fluctuations in Laser Lab causing input beam jitter Powers oscillates with 20 min period Does this input beam jitter couple into high frequency noise? Search for modulated noises analyzing long locks (up to 40 h) IMC transmission and PRC pick-off powersIMC end quadrants diodes 0.7 mHz

ILIAS WG1 meeting – Gabriele Vajente6 Analyzed configurations During C6 run: –“bump” between 100 – 300 Hz (diffused light) –removed before the end of the run During M9 minirun: –New power stabilization scheme Input laser power is stabilized using a pick-off before the IMC Input laser power is stabilized using the power transmitted through the IMC Dark fringe spectrum with and without the “bump” The “bump” was acoustic noise re- injected by diffused light at north end bench

ILIAS WG1 meeting – Gabriele Vajente7 Analysis methodology Computed DF spectrum at intervals (every 5s or 20s, 60s window length, 2 16 points for each FFT) Computed band-limited RMS: [0, 2], [2, 10], [10, 30], [30, 50], [50, 200], [200, 600], [600, 1000], [1000, 10000] Hz Time evolution and frequency analysis of these RMS

ILIAS WG1 meeting – Gabriele Vajente8 C6 lock (without bump) Spectrum of dark fringe band-limited RMS time evolution

ILIAS WG1 meeting – Gabriele Vajente9 C6 lock (without bump) Spectrum of dark fringe band-limited RMS time evolution 2 – 30 Hz Angular noise? Coherence with BS, NE, WE and ISYS angular corrections 0.6 – 1 kHz Acoustic noise from the ISYS?

ILIAS WG1 meeting – Gabriele Vajente10 C6 lock (with bump) Spectrum of dark fringe band-limited RMS time evolution

ILIAS WG1 meeting – Gabriele Vajente11 C6 lock (with bump) The “bump” is modulated at 0.38 mHz. Correlated with NE building temperature

ILIAS WG1 meeting – Gabriele Vajente12 New power stabilization scheme

ILIAS WG1 meeting – Gabriele Vajente13 New power stabilization scheme No more modulated noise! Conclusion: All these noises were acoustic/angular noises of ISYS coupled through the power fluctuations in the IMC. IMC txIMC ty IMC trans.RFC trans.

ILIAS WG1 meeting – Gabriele Vajente14 Daily trends

ILIAS WG1 meeting – Gabriele Vajente15 Daily trends During one weekend ITF locked continuously for more than 28 h with all 10 LA loops closed Clear daily trend in dark fringe power Seems to be stable between different locks Dark fringe after OMC Dark fringe before OMC PRC pick-off power

ILIAS WG1 meeting – Gabriele Vajente16 Effect on dark fringe Dark fringe demodulated signal Dark fringe DC signal Red: DF DC maximum Green: DF DC minimum

ILIAS WG1 meeting – Gabriele Vajente17 Coherences B7 DCB7 ACpB7 ACq B8 DCB8 ACpB8 ACq Control noise? Diffused light Red: B1 DC maximum, Green: B1 DC minimum B7 = NE transmitted beam B8 = WE transmitted beam

ILIAS WG1 meeting – Gabriele Vajente18 Projections of angular noises

ILIAS WG1 meeting – Gabriele Vajente19 Projections of angular noises Strong coherence of all angular corrections with dark fringe Can compute approximate transfer functions to DF without noise injections All angular error signal are coherent with each other Can “project” angular noise into DF

ILIAS WG1 meeting – Gabriele Vajente20 Projections of angular noises Strong coherence of all angular corrections with dark fringe Can compute approximate transfer functions to DF without noise injections All angular error signal are coherent with each other Can “project” angular noise into DF THIS MAKES SENSE ONLY FOR THE DOMINANT SIGNAL!

ILIAS WG1 meeting – Gabriele Vajente21 Projections of angular noises Dominant noise source is WI (under local control!) It’s possible to strongly reduce its gain (by a factor of 20)

ILIAS WG1 meeting – Gabriele Vajente22 Projections of angular noises These projections are automatically computed via an octave program Needed independent measurements of transfer functions!

ILIAS WG1 meeting – Gabriele Vajente23 Diffused light investigations

ILIAS WG1 meeting – Gabriele Vajente24 Diffused light investigations First step: 100 – 300 Hz bump coherent with north end signals Found several stray beams in north end bench The strongest one comes from the flip mount used to attenuate the beam in front of the quadrants NE beam Quadrants Dark fringe spectrum

ILIAS WG1 meeting – Gabriele Vajente25 Diffused light investigations The beam hit the bench box and was diffused When the box was open, the bump disappeared Installed a cylindrical-conical aluminum beam dump Gain in sensitivity and NS-NS horizon stability The same beam in WE bench was dumped with black foam

ILIAS WG1 meeting – Gabriele Vajente26 Diffused light investigations Second step: 100 – 300 Hz coherence with WE signals h_rec [1sqrt(Hz)] h_rec [1/sqrt(Hz)] Straylight bump Black foam was not sufficient for this beam dumping Beam hit the box not orthogonally Used black AR- coated glass

ILIAS WG1 meeting – Gabriele Vajente27 Conclusions

ILIAS WG1 meeting – Gabriele Vajente28 Conclusions Input beam jitter couples with angular/acoustic noise –disappeared using new laser power stabilization scheme Daily trends (still input beam jitter) –will be solved with ISYS drift control Stray light has a major effect! –Need to careful dump every stray beam… Angular control noise –Dominant with Local Controls –AA not yet optimized. Noise re-injected up to some tens of Hz

ILIAS WG1 meeting – Gabriele Vajente29 Spare slides

ILIAS WG1 meeting – Gabriele Vajente30 VIRGO simplified optical scheme

ILIAS WG1 meeting – Gabriele Vajente31 Power stabilization Low pass filter at 8 Hz Unity gain at 60 kHz Reduction of power fluctuations starting 10 mHz Does not correct the slow oscillation