Low Noise Suspensions and Readout Systems for Improving Advanced LIGO

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This is a collaborative research program between Vladimir Braginsky's Moscow State University (MSU) group and the Laser Interferometer Gravitational-Wave Observatory (LIGO) Laboratory. It focuses on two types of enhancements under consideration for Advanced LIGO: the use of crystalline silicon for the interferometer mirrors to reduce thermal noise, and quantum measurement techniques that can give sensitivities beyond the current limits due to quantum (shot) noise. Crystalline silicon is known to have excellent mechanical properties and has a minimum in its thermal expansion near 120 K. Operation at this point would minimize thermal noise. However, many aspects are not yet well enough understood for large scale application. Under this grant, we explore techniques for fabricating silicon ribbons for a silicon test mass suspension operating at 120 K, measure dissipation in silicon ribbon suspensions, and to find ways of minimization dissipation and thermal noise in the silicon suspensions. We investigate optical losses and other poorly measured thermal, mechanical and optical properties of pure high-ohmic crystalline silicon and other possible candidate materials for test masses from room to liquid nitrogen temperatures. Finally we analyze sources of noise in crystalline coatings applied to silicon test masses. The other main limitation to the sensitivity of Advanced LIGO will be quantum (shot) noise. We also continue the investigation of new topologies and measurement schemes for laser gravitational wave detectors, relevant to both Enhanced Advanced LIGO and beyond, and allowing us to suppress quantum noise and to relax requirements for the circulating optical power. The results of this work have a number of impacts. The most direct is that the techniques developed can be used to make gravitational wave detectors more sensitive, and thus help derive more information about the astrophysical phenomena that cause gravitational waves. Understanding the unusual conditions that create gravitational waves improves our understanding of violent processes that shape our universe exciting and inspiring students and the public. More broadly, the same techniques which are developed under this research can be used in a number of precision measurement applications in science and engineering. These include reducing noise in precison frequency reference standards to produce more accurate clocks, making quantum cryptography and quantum computing more feasible, improved tests of fundamental assumptions about space and matter, and ... finally, a major goal of this work is to foster closer collaboration on peaceful research between Russian and US scientists. This promotes better understanding between the scientific communities in these two super-powers.