diffused light studies
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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
750mW@1064nm
PM@45°
sample
diaph
L=500mm
box
Beam dump
CCD
stage
Diffused light measured @45° at 5cm from the sample with a PM of 1cm2
Homogeneity evaluated by moving the sample placed on a translation stageImage taken with a CCD camera @10cm.
w0=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:
(1”,HR@45°)
6-7 W 1200-1400ppm
Brand new from CVI:(1”,HR@45°) 3-3,5 W 600-750ppm
Fichou HR miror(3”,spare of M1 detection)
1-1,6 W 200-340ppm
First tested with the setup: a few typical commercial and customs mirrors
CCD image Light measured
B. Canuel – ILIAS WGI meeting 10/07/08
Mirrors Tests
HR quadrant alignment miror Laseroptik: 0,8-1,2W 150-250ppm
Mirror from SILO:(2”,HR@45°)
End bench spare M20,4-0,75 W 80-150ppm
CVI substrate (fused silica), coated by LMA (2”,HR@45°)
Tested by LMA@ 45 ppm:300-500nW 60-100ppm
General optics super polished, coted by LMA(2”,HR@45°)tested by LMA @ 30 ppm
70-210 nW 15-45ppm
Gain *8
Gain *24
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 (1”,HR@45°): 1400 ppm
General optics super polished, coated by LMA (2”,HR@45°): 15-45 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 0,4-1uW 80-200ppm
Optosigma plano convex 300mm 120-300 nW 25-60ppm
CVI biconvex 200mm 70-200 nW 15-40ppm
CVI biconvex 500mm 150-200 nW 30-40ppm
B. Canuel – ILIAS WGI meeting 10/07/08
Lenses tests:
Values (quite) homogenous with comparison with mirors
Ppm values closed to very good mirors 15-200ppm
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 cube10-12 W 2000-2500ppm
270-310W 55000-65000 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
2,5-4W 500-800ppm
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 reflectingWires !
B. Canuel – ILIAS WGI meeting 10/07/08
Absorbing glass70-150 nW 15-30ppm
Razor blade: medium power up to 5W
New: 40-50 W
Damaged: 80-100 W
10000 ppm
20000ppm
Very directive in the incident plane
High power from opto-sigma,up to 30W,2 inches aperture
Home made beam trap
Damage threshold1,8W@w0=1mm5,6W@w0=2,5mm
1,4 mW detected @5cm
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
EDBPZT 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
ShakerIn horizontal position
episensor
B. Canuel – ILIAS WGI meeting 10/07/08
EIB Upconverted seismic noise
quiet conditions
noise injectionwith shakerAmplitude *2
noise injectionwith shaker
Situation by exiting the bench whith noise around 10-20 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 glassLenses 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 noisemuch 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 BSto 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
shakerOther 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 absorbingGlass.
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 dumpRed: after M3Green: after M2Blue :after M1Purple: before M1
Limited by some element between M2 and M3Close 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:
))(22sin()( gtdGt
d(t) = bench displacement, given by the episensor on the benchg = 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 line @ 27 Hz...
B. Canuel – ILIAS WGI meeting 10/07/08
Evaluation of recoupling factor before the work by injecting 10- 20 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 10- 20 Hz white noise
We see at least the improvementis a factor 6....
Noise simulations and projection:EDB
EDB white 10-20 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 10-20 WEB G = 2 x 10-20
G = 2,6 x 10-20 G ~ 0,9-1,4 x 10-20 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 10-100Hz
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. 8001
Isolation Efficiency @ 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 100 -150 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 benchesShort 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.
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