The award supports (i) the search for a stochastic background of gravitational-waves of both primordial and astrophysical origin using the latest data from the Laser Interferometer Gravitational-wave Observatory (LIGO) and its international collaborators. Rather than considering the entire sky at once, the search considers individual sky regions and is expected to produce the world's best limits on stochastic gravitational radiation. Additionally the award supports (ii) the development of an all-optical trap for a small mirror, a step that could lead to improved sensitivity in next generation gravitational wave detectors. Radiation pressure, together with the optical cavity dynamics, will provide the trapping force without the need for active feed-back.
Primordial gravitational waves in the LIGO observation band were generated in the early universe at energy densities beyond the experimentally-tested regime of the Standard Model of particle physics and have the potential to reveal new physics. Observing these waves may be the biggest prize gravitational-wave astronomy has to offer. Looking beyond existing gravitational-wave detectors, optical trapping of a test mirror using radiation pressure will allow the manipulation of macroscopic objects at the quantum level, and can lead to an improved angular control system for the next-generation gravitational-wave interferometers. The project will also provide hands-on experience for undergraduate students and training for graduate students on actual LIGO interferometer hardware.
Projects Outcomes Report - NSF PHY-1068809 Intellectual merit: The Advanced LIGO gravitational-wave observatory is on the brink of providing the first direct observations of gravitational waves, opening up a new era for astronomy. The research supported by this awards aimed at facilitating the initial gravitational wave observation, and developing technologies for upgrading the LIGO gravitational wave observatory in the future. The research accomplished under this award includes the design and installation of a system to keep track of the quality of gravitational-wave data. Additionally a variety of upgrade options for Advanced LIGO were investigated. The first investigation was a study of optical configurations that would allow reducing the impact of thermal noise on the gravitational-wave interferometer sensitivity at the current LIGO facilities [PRD 88, 062004 (2013)]. A possible spin-off is the use of this configuration in reference cavities for optical frequency standards. We also investigated using existing detector technology at larger facilities. This path looked especially promising for the future. It would allow the observation of binary neutron star and black hole mergers at cosmological distance (figure) [arXiv:1410.0612]. Such a gravitational-wave interferometer could serve as the backbone observatory for gravitational-wave astronomy for many decades. One way to reduce the cost of such a facility is the use of lenses inside the interferometer arms to reduce the optical beam, and therefore the required vacuum system size. For such a configuration we identified a new type of thermal noise for lenses, related to radiative surface losses [Phys. Rev. D 90, 043013]. Additionally a novel radiation-pressure-based control scheme for optical mirrors was investigated. A setup that controls the mirror position using only the pressure exerted by light was successfully demonstrated. The optical configuration in this setup automatically adjusts the light intensity to maintain the mirror's position, without requiring any active electronic feed-back. The use of this technique for optical alignment control was investigated [PRD 89, 122002 (2014)]. Broader impact: The project supported two graduate students and one post-doctoral researcher. It also provided research opportunities for a number additional graduate and undergraduate students.
