RUI: Survey of Magneto-Optical Materials for Faraday Isolators in Future Gravitational-wave Detectors

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In the first two years after coming online following a major upgrade designed to boost their sensitivity by a factor of ten, the twin Advanced LIGO detectors have made several detections from binary black hole mergers and colliding neutron stars, opening a new era of multi-messenger astronomy with gravitational waves. To observe events from a larger variety of gravitational wave sources and to see further into the universe requires a new-generation of detectors with even higher sensitivity over a broader range of the gravitational wave spectrum. This new generation of detectors will employ higher laser powers, larger test masses of low-loss materials cooled to cryogenic temperatures, and the operation at longer wavelength of the laser, among many others. High laser power and longer wavelength present a challenge for the Faraday isolators whose performance is strongly affected by the operating wavelength, requiring the current designs to be revisited. This study will investigate new magneto-optical materials for Faraday isolators in future gravitational wave detectors, in order to identify high-performance, low-absorption candidates at wavelengths longer than one micrometer. The proposed projects will enhance the research activities in the field of experimental gravitation at Montclair State University (MSU), will train and mentor undergraduate and master's degree students, and will help them develop hands-on skills in areas of optics and lasers, spectroscopy, vacuum systems and cryogenics.The MSU group will perform spectral measurements of transmittance and Faraday rotation on several classes of magneto-optical materials at wavelengths longer than one micrometer. As the Verdet constant typically increases at low temperatures, these measurements will be carried out both at room and at cryogenic temperatures, as low as 5K. The proposed work will have a direct impact on developing and designing Faraday isolators for the future gravitational wave detectors. Early identification of suitable materials will allow for timely implementation and proper review of the new isolators.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.