ring dampers and gold barrel coatings -to control parametric instabilities chunnong zhao on behalf...
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Ring Dampers and Gold Barrel Coatings
-to control parametric instabilities
Chunnong Zhao on behalf of Gingin facility, ACIGA/UWA
UWA Experimental Team:
David Blair, Pablo Barriga, Jean-Charles Dumas, Yaohui Fan, Slawek Gras, Li Ju, Haixing Miao, Andrew Woolley, Chunnong Zhao
Current main focus:
Control of Parametric Instabilities
m
10
Acoustic mode mCavity Fundamental mode (TEM00, frequency o)
Radiation pressure force
Parametric Instability
Input light frequency o
Scattering into TEMmn,frequency 1
3-mode interaction requires frequency matching and spatial overlap of acoustic and optical modes
Current Status: Simulation
AdvLIGO predictions: 5-10 unstable modes per test mass; maximum PI gain of 10-100
PI Effects: Time to break lock
•Time to reach vibration amplitude 10-6 m: ~230 seconds
•TL time constant: hours
•RoC: not constant
0 50 100 150 200 2500
0.2
0.4
0.6
0.8
1
1.2x 10
-5
Time (sec)
Aco
ustic
Mod
e A
mpl
itude
(m)
Current Status: Experiments with Sapphire Test Masses
0.92 0.94 0.96 0.980
0.5
1
1.5
2
2.5
3x 10
-4C
ircul
atin
g T
EM
01 m
ode
pow
er (
w)
0.92 0.94 0.96 0.980
0.005
0.01
0.015
Cavity g-factors
-R
Associated acoustic mode at f=160 kHz
Associated acoustic mode at f=84 Hz
-2.55 -1.46 -1.03 -0.79ITM Effective RoC (km)
•Measured power of the TEM01 mode as a function of the ITM RoC.
•Blue line: interactions with acoustic mode at frequency of ~ 160kHz
•Red line: interactions with acoustic mode at frequency of ~84 kHz.
Simple spectrum because:
•single cavity
•small test mass
•low mode density
How to Control PI
Detuning by RoC
Reduce Qm with minimum
noise: Ring damper
2
1
1
2
0
2
10
1
/8
eff
m
minmB
L
QQQPR
m
0 : the frequency of the TEM00 mode1 : the frequency of the TEMmn mode/2Q1
Q0,1,m : Q-factors of the cavity modes,TEM00 and TEMmn, and the acoustic mode respectively
Parametric Gain:
When R>1 the
instability will occur
V. B. Braginsky, S. E. Strigin, & S. P. Vyatchanin, Phys. Lett. A, 287, 331-338 (2001)
Radius of Curvature Tuning
•Simple cavity: Black
•Marginally stable PR: Red
•Stable PR : PI gain curve will sit between these two curves
sgras@cyllene.uwa.edu.au
Optical coating
LossyStrip
Ring dampers: Q reduction with minimum noise
Gold Strip: Thermal noise spectral density vs. position
Modelling assumptions:• Full AdvLIGO test mass with flats• Best estimated of fused silica acoustic loss• Best estimated of coating acoustic loss
Model Results:• Is the thermal noise penalty acceptable?• Higher thermal noise
larger stability windows
For minimal thermal noise other control schemes are needed
Modelling AdvLIGO Ring Damper and Barrel Coating
sgras@cyllene.uwa.edu.au
Number of unstable modes with and without ring damper
•Number of unstable modes reduced to mostly <5
ETM optical coating
TN = 5.70e-21 (only optical coating)
20m ring damper, φ=5.5e-3
TN = 2.41e-21 (only ring damper)
1m barrel gold coating, φ=0.01
TN = 2.74e-21 (only gold coating)
• In best case, a few modes with R>1 per test mass
• Need other control at the same time
Other Control Schemes
• Optical feedback
• Feedback control using electrostatic actuation
• Tune stable recycling cavities
Proposed Gingin Experiment
10 W Laser & mode matching optics
11 m 72 m 3 m
M0
L2
L1
M1
M2
Configuration using existing vacuum system:
PRC: •Increase cavity the power and finesse •Tune the high order mode Guoy phase
• Maximise the Parametric gain • Study the control schemes• Study the thermal aberration • Study the ring damper
CP
Acknowledgements
• David Blair and Li Ju, UWA staff.• Slawek Gras, Pablo Barriga, Haixing Miao, Yaohui Fan:
PhD students• Guido Muller, Phil Willems, Gregg Harry: Gingin Advisory
Committee and OWG• Jesper Munch, Aiden Brooks, Peter Veitch: U Adelaide
partners• Sergey Vyatchanin, Bill Kells: theoretical discussions and
assessment.
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