development for observation and reduction of radiation pressure noise
DESCRIPTION
Development for Observation and Reduction of Radiation Pressure Noise. T. Mori , S. Ballmer, K. Agatsuma, S. Sakata, S. Reid, O. Miyakawa, A. Nishizawa, K. Numata, H. Ishizaki, A. Furusawa, S. Kawamura, N. Mio. Graduate School of Frontier Science, the University of Tokyo - PowerPoint PPT PresentationTRANSCRIPT
GWADW 2010 in Kyoto, May 19, 2010
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Development for Observation and Development for Observation and Reduction Reduction
of Radiation Pressure Noiseof Radiation Pressure Noise
T. Mori, S. Ballmer, K. Agatsuma, S. Sakata,S. Reid, O. Miyakawa, A. Nishizawa, K. Numata,H. Ishizaki, A. Furusawa, S. Kawamura, N. MioGraduate School of Frontier Science, the University of TokyoNational Observatory of Japan
GWADW 2010 in Kyoto, May 19, 2010
OutlineOutline1. Objectives and scope of the experiment2. Setup and Experiment3. Problems and Solutions4. Future plans, Summary
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GWADW 2010 in Kyoto, May 19, 2010
1. Objectives and Scope1. Objectives and ScopeObjectives
Observe radiation pressure (RP) noiseReduce radiation pressure noise
measurement of ponderomotively squeezed vacuum fluctuations at the best homodyne phase
ScopeFabry-Perot cavities with tiny mirrors and high Finesse
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Radiation pressure noise
Shot noiseSQL
Radiation pressure noise reducedat some homodyne phase
GWADW 2010 in Kyoto, May 19, 2010
Ponderomotive squeezingPonderomotive squeezingSqueezing ponderomotively
Correlating amplitude fluctuation with phase fluctuation via back actionDisplacement changed by back-action of laser light and
vacuum fluctuationsSqueezing with frequency dependence
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Laser light and vacuum fluctuations
displacementLaser light and
ponderomotively squeezed vacuum
GWADW 2010 in Kyoto, May 19, 2010
Conceptual designConceptual design Main interferometer: Fabry-Perot Michelson
interferometer with tiny mirrors (20mg) and high Finesse (10000)
Output light homodyne detected with local oscillator
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Homodyne detection
Fabry-Perot Michelson interferometer
Tiny mirrors
High finesse
signalnoise h : homodyne phase
signal×noise
GWADW 2010 in Kyoto, May 19, 2010
Noise budgetNoise budget
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Laser power 200 mW
Injected laser power 120 mW
Finesse 10000
End mirror mass 20 mg
Diameter of end mirror 3 mm
Thickness of end mirror 1.5 mm
Front mirror mass 14 g
Reflectivity of end mirror 99.999 %
Reflectivity of front mirror 99.94 %
Optical loss 50 ppm
Beam waist of end mirror 340 m
Mechanical loss of substrate
10-5
Mechanical loss of coating 4×10-4
Length of silica fiber 1 cm
Diameter of silica fiber 10 m
・ Observation of RPN; 1×10-17 [m/rtHz]@1 kHz・ Ponderomotive squeezing of 6 dB
Observation and reduction of RP noise between 300Hz and 1kHz
GWADW 2010 in Kyoto, May 19, 2010
2. Setup: Small mirror and 2. Setup: Small mirror and pendulumpendulum
Silica fiber attached on 20mg mirrorGlued with UV cured resin
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Diameter: 3mm
Silica fiber of 10m in diameterFor lower suspension thermal noiseNow 20m: due to availability
20 mg mirror with a diameter of 3mm
Effective diameter ~2mmFlat mirror
GWADW 2010 in Kyoto, May 19, 2010
Initial setup: single Fabry-Perot Initial setup: single Fabry-Perot cavitycavityFabry-Perot cavity
Cavity length: 60mm, Finesse:1400Front mirror: fixed mirror mounted on PZTEnd mirror: suspension by a double pendulum
Middle mass (aluminium): eddy-current dampedAll the core optics are on one optical table
Table is suspended by a double pendulum
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End mirror
Front mirror
Fabry-Perot cavity
GWADW 2010 in Kyoto, May 19, 2010
Assembling of a pendulumAssembling of a pendulum Very large yaw fluctuation prevented the stable locking Damping magnet: optimized for damping the yaw motion
instead of the damping for the displacement (longitudinal) motion
We could lock the cavity with this configuration(hopefully higher Eddy-current damping)much less trouble with yaw-instabilities
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uniform magnetic field (top view)
GWADW 2010 in Kyoto, May 19, 2010
3. Characteristics of the cavity3. Characteristics of the cavity
succeeded in the stable locking UGF: ~1kHzPhase margin:
~80deg.Limited by the
mechanical resonance @4.5kHz
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Open loop transfer function
Gain
Phase
dela
y
GWADW 2010 in Kyoto, May 19, 2010
SensitivitySensitivity
Estimated from the error signal
Not optimized yetElectric noise not
eliminated
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Free running laser frequency noise (in theory)
Previous measurement (20080410)
GWADW 2010 in Kyoto, May 19, 2010
4. Problem: Yaw instability4. Problem: Yaw instabilityTechnically: prevents the stable locking, and makes the alignment
very difficult and painfulTheoretically: actuated by the radiation pressure
Resonant axis is changed from center of mirror because of mirror fluctuationsYaw mode fluctuation is increased by radiation pressure → angular anti-
spring effect (S. Sakata et. al., PRD81, 064023(2010))Can be actuated easily: because of single silica fiber
Torque by radiation pressure is a factor of 1000 larger than restoring force (for final cavity power)
Angular control system needed
Now constructing
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Incident light
Front mirror
End mirror
GWADW 2010 in Kyoto, May 19, 2010
Negative g-factor is better, but..Negative g-factor is better, but..Another solution for the yaw instabilityFor yaw motion: in general always stable & unstable
mode If input mirror is controlled, small mirror becomes
- unstable for positive g-factor- stable for negative g-factor
flat mirror: always unstable If enough budget, we will try a curved one
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g=(1-L/R1) * (1-L/R2)0<g<1 for optical stability
L > R2
GWADW 2010 in Kyoto, May 19, 2010
Problem: Q –factorProblem: Q –factor
Q-factor: previously measuredFiber: 10mworse than the expected value
Pendulum mode : Q= 7360 @ 5 Hz
Thermal noise: slightly lower than designed RP noise
1st violin : Q=3975 @ 1567 Hz
Clamping section might be problem
We will measure this again, and investigate them
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GWADW 2010 in Kyoto, May 19, 2010
Future plansFuture plansNow installing;
Laser power: 200mW -> 500mWwith frequency and amplitude stabilization system
Input mirror with angular control system
Now preparing;accurate measurement of the value of the system;
Q-factor of the torsion and pendulum modeclarify where mechanical loss comes from
->Build a FP Michelson interferometer
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GWADW 2010 in Kyoto, May 19, 2010
SummarySummary
Goal: Observation and Reduction of radiation pressure noiseKey point: suspended 20 mg mirror by 10 m diameter silica
fiber
Cavity locked stably at low power improvement on the yaw motion damping
Future planLaser power upgradeStabilization of the light sourceNew input mirror suspension for yaw motion control systemBuild a full interferometer
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GWADW 2010 in Kyoto, May 19, 2010
Thank you!Thank you!
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