Our group is engaged in research to enable the success of gravitational wave detectors through close involvement with the LIGO Scientific Collaboration (LSC). The strength of the group stems from our multidisciplinary roots in the Ginzton Lab at Stanford.
The seismic isolation and alignment system for Advanced LIGO was primarily developed by a team of scientists and engineers at Stanford, as part of a large team including people at MIT, Caltech, UC Boulder, professional design firms, and the LIGO observatories.
Our seismic isolation work provides team leadership and advanced research for the ultra-quiet, precision-controlled tables where LIGO’s sensitive optics are mounted. We are currently working on continued improvement in the robust performance of those systems when faced with large environmental disturbances such as high wind and large, distant (teleseismic) earthquakes. Every additional hour of operation for these detectors is another hour of valuable observing time. We also support research into techniques to enhance the existing isolation systems to enable future gravitational wave detectors by integrating cryogenic cooling systems for the mirrors onto the seismic isolation system without compromising the positioning or vibration requirements for the optics. This work is done in close collaboration with other members of the LSC.
The LIGO Scientific Collaboration (LSC) Center for Coatings Research (CCR), funded by the NSF and the Gordon and Betty Moore Foundation, seeks to extend the reach of the next generation of gravitational wave detectors by addressing the dominant noise source limiting their performance, thermal noise in the interferometer mirrors. This noise reduces the number of observable gravitational wave signals from astronomical sources. It arises from thermal excitation of the vibrational modes of the mirrors in the LIGO detector optics. The effect of these excitations is reduced as the mechanical quality factor (Q) of the mirrors is increased. Since the Q of the mirrors is limited by the reflective coatings deposited on their surfaces, lower noise requires development of better coatings. The CCR combines groups from 10 institutions in the US working on computational modeling of amorphous materials, deposition of coatings, and characterization of their atomic structure and macroscopic properties. These components are often performed by three diverse communities that work in relative isolation from each other. The strength of the CCR and its promise of accelerating discoveries arises from close integration of these three communities focused on a unified research goal. Coating thermal noise is also a limiting factor in the fields of precision timing, quantum information, low noise interferometry, and precision measurements like the search for deviations in the gravitational inverse-square law. Coatings improving on the state of the art in mechanical and optical properties developed under this program would be applicable to these communities as well.
Combining with our CCR efforts, Stanford has had a leading role within the LSC in developing experimental methods to characterize the optical, elastic, and structural properties of the amorphous materials composing multilayer dielectric mirrors. Florida carries out the current computational materials modeling effort within LSC. Our collborative research program is a synergistic teaming to combine these skill sets to address a critical issue to meet the design goals of A+LIGO, developing mirrors with 2-4 times less mechanical loss than the best currently available. The mechanical losses in amorphous materials depend on subtle, preparation-dependent features in their atomic structure. Data on these structural features obtained via the electron diffraction and X-ray scattering methods are challenging to interpret, as are molecular dynamics predictions of the structure. Methods exist to use the modeling to help interpret the data and the data to help constrain the modeling, which led to the teaming with Hai-Ping Cheng's group at the University of Florida. The structural data and predictions for dependence of elastic losses on material composition and process conditions, will become a major contributor to the broader LSC program to develop mirrors for A+ LIGO, guiding the others working on this problem through the thicket of possible synthesis and characterization experiments.
Another long-standing effort at Stanford has been in the optical characterization of low-optical loss materials at the sub-ppm/cm level, dating back to the downselect between silica and sapphire for initial LIGO test masses. We have recently begun using the interferometric tool developed for those studies to characterize cryogenic losses in single-crystal silicon samples to evaluate their suitability as testmasses in the planned cryogenic LIGO Voyager.