Sensors for Low-Frequency Improvements in Advanced LIGO

University Of Washington, Seattle WA

Investigators

Abstract

Last February, Advanced LIGO detected gravitational waves for the first time, opening a new window to the universe. This award supports the development of new equipment to be deployed at the LIGO sites in Hanford, WA, and Livingston, LA. This consists of a high precision inertial tilt sensor to measure horizontal tilt independently from horizontal acceleration, which will improve Advanced LIGO seismic isolation, enabling robust operation of the interferometer under adverse environmental conditions. Research on tilt sensors will have a broader impact in areas such as seismology and geophysics by enabling measurement of tele-seismic tilts and tilt-free ground acceleration at frequencies as low as 10 mHz. The high precision angle readouts developed for these tilt sensors have a wide variety of applications in metrology and precision experiments. This award not only supports the development of a device for Advanced LIGO, but it also serves to maintain and strengthen synergistic activities of this table-top gravity group with the gravitational wave detection community. Importantly, this STEM research will train undergraduate and graduate students, and postdocs in building precision mechanical instruments. In LIGO's transition from Detector to Observatory, maintaining high duty cycles is a key challenge. Environmental conditions such as high wind, microseism and earthquakes were primarily responsible for significantly limiting the duty cycle during the first observing run. This is due to the inability of seismometers to distinguish between low-frequency tilt and translation, known as tilt-horizontal coupling. The ground-tilt sensors the group has developed have been demonstrated to improve the low-frequency seismic isolation in LIGO. Further improvement by making them smaller and more sensitive with interferometric readouts, would allow them to be mounted directly on the isolated platforms from which the LIGO mirrors are suspended, enabling a stronger and direct benefit to low-frequency differential motion of the mirrors. In addition, they may prove useful in measuring seismic tilts in the gravitational wave-signal band between 5-30 Hz, allowing cancellation of Newtonian noise, which is expected to limit sensitivity of aLIGO and future detectors.