Realistic filter cavities for advanced gravitational wave detectors

The ongoing global effort to detect gravitational waves continues to push the limits of precision measurement while aiming to provide a new tool for understanding both astrophysics and fundamental physics. Squeezed states of light offer a proven means of increasing the sensitivity of gravitational wave detectors, potentially increasing the rate at which astrophysical sources are detected by more than 1 order of magnitude. Since radiation pressure noise plays an important role in advanced detectors, frequency-dependent squeezing will be required. In this paper we propose a practical approach to producing frequency-dependent squeezing for Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and similar interferometric gravitational wave detectors. This work focuses on ``realistic filter cavities'' in the sense that optical losses in the filter cavity and squeezed light source consistent with current technology are considered. The filter cavity solution proposed for Advanced LIGO is ``practical'' in that it considers the nonquantum noise and readout scheme of the interferometer and a potential implementation geometry in the Advanced LIGO vacuum envelope.