LIGO Document G1300718-v1

Design and development of a suspension platform interferometer for the AEI 10m Prototype Interferometer

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The AEI 10m Prototype interferometer is a facility for developing and testing novel techniques for advanced gravitational wave detectors. It is also an environment for performing measurements at and beyond the standard quantum limit (SQL). Therefore, a vacuum system with a volume of 100mł in an L shaped configuration is installed to house experiments, such as the sub-SQL interferometer. Three optical tables are placed inside the vacuum envelope. The optical tables are suspended by pendulum stages to isolate the experiments from seismic motion. These isolation benches are referred to as AEI-SAS (seismic attenuation systems). Below the resonance frequency of the pendulums the optical tables are not decoupled from the ground motion. Hence, we have designed and built a suspension platform interferometer (SPI) to stabilize the differential table motion in the frequency range from 10mHz to 100mHz down to 100pm/sqrt(Hz) in longitudinal displacement and 10nrad/sqrt(Hz) in angular displacement. The SPI senses the relative motion of the three SAS in five degrees of freedom by heterodyne interferometry and differential wavefront sensing. The interferometric signals are used in a feedback control system to stabilize the SAS relative to each other, so that one rigid platform is formed. The design of the SPI and the first measurements will be presented.
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