Devices and Materials for the Instrument Science of Advanced Gravitational-Wave Detectors

Gravitational waves are the messenger that will tell us about some of the most highly energetic events in the universe, in this case the coherent motion of very heavy masses undergoing high acceleration; such large masses can be found in black holes, the merger of neutron star binary systems, supernovae, and the echoes of the big bang. The discovery of gravitational waves as well as the discovery of these sources with Advanced LIGO, the Laser Interferometer Gravitational Wave Observatory built by the National Science Foundation to make a direct detection of gravitational waves, would be a major milestone in the history of science. Advanced LIGO encompasses an extremely diverse array of underlying scientific and engineering disciplines: examples include lasers, optics, low noise electronics, control systems, grid computing, algorithm development, and handling large data sets.

The Advanced LIGO interferometers have turned on and commissioning of them has increased their sensitivity far above previous detectors. The goal of a tenfold sensitivity improvement is in sight. Because the search volume scales as distance cubed, advanced LIGO will have more than 1000 times more sources within its reach. To achieve this improved sensitivity, essentially everything except for the vacuum system has been replaced. This includes the use of a 180 Watt laser, quadruple pendulum suspensions, 40 kilogram test masses, active seismic platforms, a signal-recycled interferometer, stable recycling cavities, an output mode cleaner, DC readout, and improved thermal compensation. The higher laser power presents challenges for the input optics, a responsibility of the University of Florida. Moreover, this research has impacts that go beyond gravitational wave science. High-power optical devices developed in this project have commercial applications in the laser and optics industries.

This project will address items that could be needed in order to optimize the performance of the detector. It also addresses basic research needed for future upgrades and next generation detectors, which will further increase the science reach of the observatories as well as work on detector characterization. Simulations of the interferometers will be carried out to aid commissioning work. Work on thermal adaptive mode-matching and devices for beam-jitter suppression will be done. A novel scheme for sensing alignment errors will be modeled and prototyped. Thermal coating noise as a function of temperature will be measured. Looking further into the future, experiments to measure impurities and free carrier absorption in high purity silicon for test masses will be conducted. Considerable effort will be put towards improving the bidirectional throughput of Faraday isolators that are key components of a squeezer for future detectors.