Improving sensors for low-frequency gravitational wave detection

LIGO is limited below 20Hz by control and seismic noise. Reducing this noise will allow us to improve the measurement of a binary merger, learn more about the progenitor objects, and increase potential for multi-messenger astronomy. Additionally, higher mass and redshift binaries would be detectable. This is a primary goal of future ground-based detectors and upgrades. 

Better seismic sensors are critical to achieve these goals, including displacement sensors which are used to damp modes of the multi-stage pendulum which suspends the interferometer optics. To improve damping, sensors should be placed closer to the optic to enable greater control authority, reducing the control bandwidth required and subsequently the control noise. The sensors currently employed by LIGO are too noisy to use in this location making improved sensors necessary. Compact interferometers are a promising technology for this purpose and multiple have been developed which should meet the required performance. 

The threshold for technology integration into LIGO is high due to the intricacies and sensitivity of the detector, so testing in a LIGO prototype facility is required to verify performance and impact on the interferometer. This talk will describe an experiment measuring a mass with three of the compact interferometers which could be used in the sensor upgrade to compare their performance, verify successful integration with the detector and subsequently decide which technology to move forwards with.