B. Canuel – ILIAS WGI meeting 10/07/08 Diffused light Studies Outline... Measures of diffused light performed in the EGO optics lab Mitigation work on the different virgo benches (EDB, EIB, end benches) How it is recoupled: noise simulations and projections for EIB and EDB Results on sensibility Conclusions

B. Canuel – ILIAS WGI meeting 10/07/08 Measures of diffused light performed in the EGO optics lab

B. Canuel – ILIAS WGI meeting 10/07/08 Measures of diffused light performed in the optics lab Beam dump sample diaph L=500mm box Beam dump CCD stage Diffused light at 5cm from the sample with a PM of 1cm 2 Homogeneity evaluated by moving the sample placed on a translation stage Image taken with a CCD w 0 =1,2mm Derive a value of total diffused light Cross-check with LMA characterization for mirrors: quite good agreement Make comparisons between very differents elements Experimental setup:

B. Canuel – ILIAS WGI meeting 10/07/08 Mirrors Tests total scattering Typical used mirror from CVI: 6-7  W ppm Brand new from CVI: 3-3,5  W ppm Fichou HR miror (3”,spare of M1 detection) 1-1,6  W ppm First tested with the setup: a few typical commercial and customs mirrors CCD imageLight measured

B. Canuel – ILIAS WGI meeting 10/07/08 Mirrors Tests HR quadrant alignment miror Laseroptik: 0,8-1,2  W ppm Mirror from SILO: End bench spare M2 0,4-0,75  W ppm CVI substrate (fused silica), coated by LMA Tested by 45 ppm: nW60-100ppm General optics super polished, coted by LMA tested by 30 ppm nW15-45ppm Gain *8 Gain *24 Gain *8

B. Canuel – ILIAS WGI meeting 10/07/08 Mirrors tests: Huge difference between the different tested mirors... Commercial mirrors widly used on virgo benches really worse by one order of magnitude than customs from SILO or coated substrates from LMA and 2 orders of magnitude from superpolished ones. Typical used mirror from CVI 1400 ppm General optics super polished, coated by LMA ppm According to LMA values of a few ppm are reached on some superpolished...

B. Canuel – ILIAS WGI meeting 10/07/08 Lenses tests Optosigma plano convex 200mm 0,4-1uW80-200ppm Optosigma plano convex 300mm nW25-60ppm CVI biconvex 200mm nW15-40ppm CVI biconvex 500mm nW30-40ppm

B. Canuel – ILIAS WGI meeting 10/07/08 Lenses tests: Values (quite) homogenous with comparison with mirors Ppm values closed to very good mirors ppm But lots of local defaults (dots ?)

B. Canuel – ILIAS WGI meeting 10/07/08 “standard” LAPP model Reduced beam size of around 100  m LAPP model with polarizing cube  W ppm  W ppm Photodiodes and quadrants Additional problem: beam size on these photodiodes increasing the recoupling ?? window photodiode

B. Canuel – ILIAS WGI meeting 10/07/08 Photodiodes and quadrants 2,5-4  W ppm NIKHEF quadrant model used for alignment Low optical quality of the window (dots) Surface quite homogenous Quite good in comparison with photodiodes New BMS quadrant photodiodes (UDT sensors) 10  W 2000ppm 100  W 20000ppm Bright and very reflecting Wires !

B. Canuel – ILIAS WGI meeting 10/07/08 Absorbing glass nW15-30ppm Razor blade: medium power up to 5W New:  W Damaged:  W ppm 20000ppm Very directive in the incident plane High power from opto-sigma, up to 30W,2 inches aperture Home made beam trap Damage threshold 0 =1mm 0 =2,5mm 1,4 mW Beam dump studies Need good HP Beam dump..

B. Canuel – ILIAS WGI meeting 10/07/08 Mitigation work on the different benches (EDB, EIB, end benches)

B. Canuel – ILIAS WGI meeting 10/07/08 Tools used for hunting diffused light Shaker placed on the different benches to introduce seismic white noise or lines. Mesures with episensensor placed on the benches (3 axis seimic sensor 0,2-200Hz). Used the “radio dark fringe” to perform tapping test Realized several beam dump with absorbing glass (for big and powerful beams with two absorbing glasses glued with a small angle) We can see if the level of seismic noise reintroduced by diffused light on the dark fringe is improved by some action on the benches...

B. Canuel – ILIAS WGI meeting 10/07/08 External detection bench EDB PZT accelerometer episensor shaker - B1s beam dump - mirror M50, M52, M1p1 - lens L52 - B5 polarizer cube Critical elements identified by listening to the dark fringe:

B. Canuel – ILIAS WGI meeting 10/07/08 Improvements on EDB B1s beam dump (razor blade type) replaced by lens (f=-0.05) + beam trap (absorbing glass). Diode mounted on top of the B5 polarizer cube removed All the other optics were un-mounted and cleaned, mounts replaced with stiffer ones. (This model of diode scatters a lot of light)

B. Canuel – ILIAS WGI meeting 10/07/08 Improvements on EDB New tapping test performed: Clear improvement for all of them apart from M1p1 (too thin mirror, too be replaced…) no more visible Up-converted noise. quiet conditions noise injection before modifications noise injection after modifications Improvement on the dark fringe …

B. Canuel – ILIAS WGI meeting 10/07/08 EIB investigations Shaker In horizontal position episensor

B. Canuel – ILIAS WGI meeting 10/07/08 EIB Upconverted seismic noise quiet conditions noise injection with shaker Amplitude *2 noise injection with shaker Situation by exiting the bench whith noise around Hz using the shaker...

B. Canuel – ILIAS WGI meeting 10/07/08 EIB investigations Most critical : B2_M1, B2_M1 Actual source of the light: reflection on B2_L1, B2_L2 B2_M1 and B2_M1 cleaned, B2_L1and B2_L2 misaligned and reflections dumped with absorbing glass Lenses of Q21 and Q22 telescope misaligned : no visible effect

B. Canuel – ILIAS WGI meeting 10/07/08 Improvements on EIB Improvement on the dark fringe … Up-converted noise much reduced quiet conditions noise injection before modifications noise injection after modifications No more obvious source of scattered light (also tested: replacement of standard beam dumps by home made absorbing glass with no effect)

B. Canuel – ILIAS WGI meeting 10/07/08 NEB investigations episensor shaker Identified at first Check up: very small clipping, reflection of quadrant not well dumped.. Biggest contributions: splitter just before the 2 photodiodes photodiodes themselves The group splitter + photodiode is moved by 50 cm upstream, some absorbing glass is glued on the BS to dump the reflection on photodiodes. Beamsize: 200 to 600  m. Lowered backscattering rate

B. Canuel – ILIAS WGI meeting 10/07/08 Results of the firts check up of NEB quiet conditions noise injection before modifications noise injection after modifications Second check up....

B. Canuel – ILIAS WGI meeting 10/07/08 NEB second check episensor shaker Other problems found: 5 or more secondary beams visible after M2 but still very close from the main beam. They have different sizes and angles (suspect the NE second face, the doublet multi reflections, the second faces of M1 and M2) some clipping on NEB_M_Flip NEB_M_Flip beam dump replaced by absorbing Glass.

B. Canuel – ILIAS WGI meeting 10/07/08 Results of the second check up... Comparison of noise level (while injecting noise) before and after these modifications...

B. Canuel – ILIAS WGI meeting 10/07/08 Remaining noise... Shaking amplitude multiplied by a factor 2... Noise with beam dump placed at different places Black: no beam dump Red: after M3 Green: after M2 Blue :after M1 Purple: before M1 Limited by some element between M2 and M3 Close to the noise probably due to the lentone

B. Canuel – ILIAS WGI meeting 10/07/08 WEB investigations Same work as the NEB performed: - moved the diodes upstream by 50cm (beam size is now 800um instead of 200um) - absorbing glass placed on diode reflections -dumped various secondary beams -misaligned a bit more the quadrants. -Multiple beams after M2 correctly dumped by absorbing glass.

B. Canuel – ILIAS WGI meeting 10/07/08 Noise simulations and projections for all the benches (Thanks to Irene Fiori)

B. Canuel – ILIAS WGI meeting 10/07/08 Effect of back scattered light on the dark fringe... Backscattered light creates noise by seismic movement of the benches: How can we model this recoupling ? Contribution to dark fringe of a parasitic beam that is delayed by a scattering surface moving by d(t) and then recombines in the ITF: d(t) = bench displacement, given by the episensor on the bench g = 1 – 1.6, adjusted to best batch the upconv. bumps (accounts for a scattering surfaces that moves up to 60% more than the bench) G = adjusted to best match the sensitivity measured [h/sqrt(Hz)] Values of G determined by seismic injection can be used to: Caracterize the diffused light mitigation on the bench Compare the recoupling rates of the different benches Make the projection of quiet seismic noise on the benches on the dark fringe...

B. Canuel – ILIAS WGI meeting 10/07/08 Noise simulations and projection:EDB Evaluation of recoupling factor before the work by injecting a 27 Hz...

B. Canuel – ILIAS WGI meeting 10/07/08 Evaluation of recoupling factor before the work by injecting Hz white noise Noise simulations and projection:EDB Quite good agreement...

B. Canuel – ILIAS WGI meeting 10/07/08 Evaluation of recoupling factor after the work by injecting Hz white noise We see at least the improvement is a factor Noise simulations and projection:EDB EDB white HZ, after works (april 18) Simulation

B. Canuel – ILIAS WGI meeting 10/07/08 Noise simulations and projection:EDB Projection of quiet bench displacement on the dark fringe before and after the mitigation The level of diffused light introduced by the movement of the bench is now under the design

B. Canuel – ILIAS WGI meeting 10/07/08 Noise simulations and projection:EIB Evaluation of recoupling factor before and after the work by the noise injections 3,8e-20 1,2e-20 Improvement more than a factor 3...

B. Canuel – ILIAS WGI meeting 10/07/08 Projection of quiet bench displacement on the dark fringe before and after Noise simulations and projection:EIB Good improvement close to the design sensitivity...

B. Canuel – ILIAS WGI meeting 10/07/08 G = 9 x WEB G = 2 x G = 2,6 x G ~ 0,9-1,4 x NEB Evaluation/results of the improvement for the terminal benches Noise simulations and projection: terminal benches

B. Canuel – ILIAS WGI meeting 10/07/08 Situation of projected noise after mitigation Main contributions of the WEB and NEB, then comes the EIB and the EDB: Major noise contribution is associated to the bench mechanical resonances (10-20Hz). Required for Virgo+: Reduce the bench motion at the resonances (factor 5 is needed) for NEB, WEB and EIB Required for Virgo++/Adv Virgo: A factor 100 is required around the resonnances and 10 in the range of Hz

B. Canuel – ILIAS WGI meeting 10/07/08 To go further: passive damping of vibration of the benches Effect of placing a resonator on the benches to selectively damp the vibrations (around the resonance of the benches) Effect of the resonnator for the NEB Tested on this bench: improvement by a factor of 3... An other factor 2 needed to reach V+ specs (fine tuning to be done...) To be tested on all the benches.... Other resonnances to damp...(55Hz...) 55 Hz

B. Canuel – ILIAS WGI meeting 10/07/08 To go further: Placing the benches “on the ground”? Example of WEB... Seismic noise on the ground is much smaller! Good improvement. Remaining bumps are due to AC machines the cooling fans of the turbo pump... To reach the AdV design, some damping seems necessary...

B. Canuel – ILIAS WGI meeting 10/07/08 To go further: Using active isolation Active Feedback Vibration Control system provides fast response and control of vibrations Vibration Isolation for all six translational and rotational modes of vibration Ultra low natural frequency < 1 Hz No low frequency resonance Isolation beginning at 0.7 Hz Kinetics system mod Isolation 10Hz 99%

B. Canuel – ILIAS WGI meeting 10/07/08 To go further: Using active isolation Good improvement. Results close to the AdV design. It seems that the 0,7Hz resonnance of the platform is much spoiling the isolation. Long term stability should be evaluated.

B. Canuel – ILIAS WGI meeting 10/07/08 Results of the improvements

B. Canuel – ILIAS WGI meeting 10/07/08 Resulting improvements Clear gain on sensibility for frequencies under Hz Reduced up- conversion by back scattering

B. Canuel – ILIAS WGI meeting 10/07/08 Resulting improvements (2) improvement on quadrant demodulated signals after cleaning optics on their beam path improvements in longitudinal error signals during diffused light mitigation.

B. Canuel – ILIAS WGI meeting 10/07/08 Conclusion We are thinking about setting up a permanent test facility... Orders of magnitude identified between elements, the worse are not the most obvious ones (lenses vs mirors). Lower the diffused light rate on the optics side We should be very careful using standard HR mirors (replace some critical mirors ?) Take care about cleanless! Precise effect of incident angle on backscattering.... Design High power beam dump... Lower the seismic exitation of the benches Short timescale: reduce the benches resonnances by resonnant damper of using stiffer benches structures. Longer Timescale: study the use of active damped benches or passive systems in combination with external control of benches absolute position.