The Stanford gravitational wave research program is engaged in research and development on gravitational wave detection for the LIGO (Laser Interferometer Gravitational Wave Observatory) program through its membership in the LIGO Scientific Collaboration. The Stanford group's current objectives are guided by the LIGO 2008 Instrument Science Priority Matrix, and are devoted almost entirely to reducing risk and insuring the success of Advanced LIGO. Its major focus is on the development of highly sensitive optical coating and bulk optical absorption loss measurements, the effects of ultra-violet illumination on LIGO optical coatings, studies of dielectric coating and test-mass elastic dissipation, and the design of advanced seismic isolation systems and suspensions. Continuing improvements in these areas are sought for Advanced LIGO to increase its sensitivity and improve the likelihood for detections of gravitational waves. Studies on understanding and minimizing thermal noise in the detector's core optics are being pursued to enhance Advanced LIGO's sensitivity in the critical intermediate frequency band. Improved core optic suspensions and isolation platforms are being developed to enable higher sensitivity at low frequencies where ground vibrations currently limit performance.

Gravitational waves were predicted almost 90 years ago in Einstein's General Theory of Relativity, but they have not yet been directly detected due to the extreme sensitivity required. Interacting black holes, coalescing compact binary stellar systems, stellar collapses, pulsars and low mass X-ray binaries are all possible sources of gravitational waves, as is the random background of radiation from the early universe. The first generation of laser interferometer detectors, which operate by measuring strains in the fabric of space-time expected to be produced by gravitational waves, have collected data for several years. Second generation, higher performance detectors, such as Advanced LIGO now under construction, should allow us to develop gravitational wave astronomy as a new window on the Universe. The Stanford group has a strong, multidisciplinary program in developing the technology for such detectors. Participants include mechanical, electrical and control engineers, physicists and materials researchers. The program provides training for future scientists and engineers at both the undergraduate and graduate levels, it integrates basic scientific research with scientific education, and it develops and funds outreach programs that inform and educate the broader community.

Project Report

Stanford is engaged in research and development on gravitational wave detection for the LIGO (Laser Interferometer Gravitational-wave Observatory) program through its membership in the LIGO Science Collaboration and through its collaborative studies with the LIGO Laboratory. The Stanford group, over the past 20 years, has made many contributions to the NSF-funded LIGO program, past and present, and we continue to look ahead for enhancements to possible future detectors. Current objectives are focused on reducing risk and insuring the success of aLIGO, which is now nearing the end of its construction phase. We are also developing advanced technologies for possible upgrades to aLIGO and for potential future generations of gravitational wave detectors. The Stanford group provides the science lead for the aLIGO seismic isolation subsystem. We have worked with the aLIGO team to commission the isolation systems. These tables are 100 to 1000 times quieter than the ground (at frequencies above 1 Hz) and provide well-controlled, ultra-quiet mounting platforms for the aLIGO optics. Those platforms are installed and working well. We have developed techniques to allow the control systems to provide improved isolation, including feedforward on reactive structures and real-time control adjustment (i.e. blend switching). We have developed new tools to integrate the isolation subsystem into the detector, including improved watchdogs, system watchdog integration, and motion monitor projection. We have contributed to improved operation time and simplified user interfaces, and we have made progress in implementing real-time fault monitoring. One of our key contributions to aLIGO is the work our team carries out on a daily basis with the team at the LIGO detector sites, where we help answer questions and discuss the many issues that arise as our systems are integrated into the detector. Our team has also led in the development of seismic isolation technologies for future detectors. We have demonstrated a ‘seismic platform interferometer’ to optically connect adjacent isolation platforms and improve their performance below 1 Hz. We have studied several ways to integrate cryogenics onto existing platforms using prototypes developed at Stanford. This would allow a new generation of LIGO capable of being cooled to very low temperatures to reduce the thermal noise and improve the detector performance. We have shown that conductive cooling for the initial cool-down of test-mass optics is possible, and have shown that slowly flowing cryogens could potentially be used to remove heat without introducing excess noise to the detector system. Test-mass optics and optical coating studies remain critical areas of research to achieve low thermal noise, which currently limits aLIGO’s sensitivity. We have developed very sensitive instrumentation for measuring the optical absorption of aLIGO optical test mass coatings, and are working with the LIGO Laboratory and their coating vendors to produce coatings with the lowest possible losses. The fundamental nature of optical coatings using extended X-ray absorption fine structure (EXAFS) measurements at the Stanford Synchrotron Radiation Lightsource, nuclear magnetic resonance (NMR) spectroscopy, transmission electron microscopy and optical Raman spectroscopy. This powerful and unique combination of tools aims to uncover the underlying mechanisms for mechanical loss, which is directly related to thermal noise, at the atomic level. We have studied the material properties of test amorphous oxide coatings, and have made significant advancements in understanding their fundamental material properties. We have used these studies to directly compare and correlate changes in coating atomic structure with changes in mechanical loss. Collaborative studies with atomic modeling experts are focusing on what causes individual atomic bonds to shift under mechanical stresses, and how this contributes to mechanical loss. Our aim is to utilize this knowledge to direct the development of high-performance coatings with lower mechanical loss, and therefore lower thermal noise. We are developing custom optical coatings designed to bleed off localized charges from the main test masses in aLIGO, which would allow a reduction of excess charge noise. Thin films of electrically conductive materials, such as alumina-doped zinc oxide and related high optical index materials are being studied to determine if their electrical conductivity and their optical loss properties can be simultaneously brought within the aLIGO performance limits. We are collaborating with a local coating vendor (MLD) to leverage their production capabilities. A new class of low-loss single crystal thin film coatings has also been developed. Molecular beam epitaxy (MBE) deposition of (Al)GaP onto silicon, developed at Stanford, has potential to replace traditional amorphous coatings on the test-mass optics in future cryogenic detectors. We have fabricated test AlGaP coatings, which have demonstrated a 15 fold reduction in mechanical loss.

National Science Foundation (NSF)
Division of Physics (PHY)
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Pedro Marronetti
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Stanford University
Palo Alto
United States
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