Active Vibration Isolation using a Suspension Point Interferometer

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Active Vibration Isolation using a Suspension
Point Interferometer
Youichi Aso Dept. Physics, University of Tokyo
Feb. 20 2004
ASPEN Winter Conference on Gravitational Waves
_at_ ASPEN Center for Physics LIGO-G040227-00-Z
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Introduction
Suspension Point Interferometer (SPI)
Active vibration isolation method
using a laser interferometer itself
Originally proposed by Prof. R. Drever
Low Freq., Improve Stability, Cryogenic
Interferometer
Prototype Experiments
Current experiment Combination of SPI and VSPI
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Contents

• SPI
• Principle
• Advantages, Applications
• Proto-Type Experiment
• VSPI
• Principle
• Proto-Type Experiment
• SPIVSPI
• Overview
• Experimental apparatus
• Development Status, Future plans
• Summary

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Suspension Point Interferometer
For GW detection
PD's
Lasers
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Working principle of SPI
Lock SPI
Rigid bar
Laser
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Working principle of SPI
Vibration is suppressed
Rigid bar
Laser
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Advantages and Applications
High performance active vibration isolation system
Seismic vibration
Cryogenic Interferometer
Vibration isolation of heat links
Stabilization
Easy lock acquisition
Actuator noise reduction
Coincidence Analysis
Dual Band
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Theoretical performance
Main factors
Control Gain
CMRR
Coupling from other degrees of freedom
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Asymmetry in the suspension
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at high frequencies
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Prototype experiment
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(No Transcript)
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Results from the proto-type experiment
Triple pendulum Fabry-Perot Cavity
Vertical vibration is dominant above 3Hz
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Transfer function measurements
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WFS test
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Vertical Suspension Point Interferometer
Goal
Stop the lower mass in the inertial frame
Assumption
External disturbances are only introduced from
the suspension points
Upper
Reference
More sticky to the inertial frame
Lower mass
Lower
Fabry-Perot Interferometer
Relative motion between the upper and lower mass
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VSPI Experiment
PDH Method
Photo Detector
?/4
Laser
EOM
PBS
Coil-Magnet Actuators
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Results of the VSPI experiment
Working fine up to 10Hz
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Next Step
Combination of SPI and VSPI
Aim
Achieve good vibration isolation
performance above the resonant freq. of the
pendulum.
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Overview of experimental setup
MC
Laser
EOM
EOM
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MGASMonolithic Geometric Anti Spring
Low freq. vertical spring
MGAS filter 1
Damping mass
MGAS filter 2
SPI mass
Eddy current plate
Recoil mass
Main mass
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Noise Budget
V-H Coupling 1 Asymmetry 1
Last stage40cm pendulum Other stages 20cm
Wire Q1000 Mirror Q10000
100mW at input Finesse 500
torr
Vacuum
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Development Status
Vacuum Chamber done
Suspension design done
MGAS test done
Optical components done
Waiting for the suspension parts to arrive
To Do
Test the suspension system
Electric circuits
Assemble the whole system
Noise hunting
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Summary
SPI, VSPI
High performance active vibration isolation scheme
Next generation detectors
Prototype experiments
Good results below the resonant freq. of the
pendulums
Limited by vertical vibration
Next experiment
SPI MGASF VSPI
better vertical vibration isolation
Test and assembly of the suspension is going on