Measuring Attometer-Scale Thermal Fluctuations in Optical Coatings for Applications in Gravitational Wave Detection

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With the detection of Gravitational Waves (GW) by the Advanced Laser Interferometric Gravitational-Wave Observatory (LIGO) a new window to the Universe has been opened. These first detections only mark the beginning of a process to make LIGO more sensitive, increasing the detection rate with each step along the way. One of the most important open problems in LIGO noise reduction is related to the coatings of the mirrors used in the interferometer. Advances in precision optical measurement have made it possible to measure the thermal fluctuations of macroscopic materials. Thermal fluctuations in mechanical systems which occur at the atto-meter scale, and are known as "thermal noise", are a limiting noise source in gravitational wave detectors and in the best frequency references. This work will expand the scope of an ongoing experiment at MIT which was used to measure the thermal noise of Advanced LIGO mirrors. The new scope will include characterizing potential replacements for the coatings currently used in gravitational wave detectors.The founding principle of the experiments supported by this award is that the thermal noise experienced by different spatial modes of a resonant cavity is easily separated from most technical noises, making a high signal to noise measurement possible in a tabletop experiment. These studies will test new materials used for ion-beam-sputtered (IBS) coatings, searching for new promising candidates to replace the coatings currently used by LIGO. Research in the area of coating thermal noise will allow us to extend the reach of gravitational wave detectors, make more precise clocks, and probe more deeply the quantum nature of opto-mechanical interactions. Since the proposed work will have a strong influence on the design of future gravitational wave detectors, its urgency cannot be overstated.