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RUI: Investigations of Mirror Thermal Noise for Gravitational Wave Detectors

RUI：引力波探测器镜面热噪声研究

基本信息

批准号：
2208079
负责人：
Steven Penn
金额：
$ 6万
依托单位：
Hobart and William Smith Colleges
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2022
资助国家：
美国
起止时间：
2022-07-01 至 2024-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2208079&HistoricalAwards=false
关键词：
RUI Investigations Mirror Thermal Noise

项目摘要

In 2015 NSF's LIGO (Laser Interferometer Gravitational-wave Observatory) launched the field of gravitational wave astronomy with the first direct detection of gravitational waves. LIGO detects gravitational waves, the ripples in spacetime, using an “L”-shaped detector, known as an interferometer, with 4 km long arms. Gravitational waves cause tiny differential stretching in the arms, which is measured by reflecting laser light off mirrors at the end of each arm and comparing the reflected beams. One of the main limits to LIGO’s sensitivity is that the mirror surfaces move as a result of thermally-induced vibrations. Known as thermal noise, these vibrations mask the gravitational wave signal. This research project will investigate a means for reducing this “coating thermal noise” by using a mirror coating formed from layers of crystalline semiconductor materials. Initial measurements indicate that this crystalline coating will lower the coating thermal noise by a factor of ten. As a result LIGO will be able to see several times farther out in the universe, with a dramatic increase in its rate of observing black holes and neutron stars. This rapidly growing catalogue of observations will inform current models of the composition, formation, and evolution of our universe. Answering the fundamental questions about the universe are ideas that excite, unite, and inspire all of humankind.The focus of this research program is the continued development of the GaAs/AlGaAs crystalline coating for use in the next major upgrade of the LIGO detectors. In addition to having excellent optical properties (scatter 10 ppm, absorption 1 ppm), these coatings have demonstrated an extremely low elastic loss. The dominant source of coating thermal noise (CTN) for crystalline GaAs/AlGaAs is thermo-optic (TO) noise, which is the combination of thermo-elastic (TE) and thermo-refractive (TR) noises. Using TO optimization, one can adjust the coating layer thicknesses so that the TE and TR effects are cancelling. These TO-optimized coatings have demonstrated a 10× lower CTN than the current LIGO coatings. While these results are extremely encouraging, a great deal of work remains to be able to realize these gains in LIGO mirrors. The measurements, to date, have been performed on small (≤ 75 mm) samples. This project oversees the development of these crystalline coatings to 20- and eventually 30-cm diameters, which are suitable for LIGO. The PI is working with the LIGO Lab to test the surface uniformity and optical properties at increasing sizes. The PI is collaborating with the Syracuse University group on tests of possible electro-optic noise and on the development of a new arm-locking system using 2 µm lasers. The PI is developing a finite element model of the coating to accurately predict the CTN. In parallel he is working with the MIT LIGO Lab group to improve the sensitivity of their CTN experiment so that it is capable of measuring the low CTN observed in GaAs/AlGaAs crystalline coating . The PI is collaborating with colleagues at Embry-Riddle, American, and Stanford to test possible birefringence noise. Finally the PI is exploring interferometer designs that could utilize the currently available 20-cm GaAs/AlGaAs coatings, rather than waiting to deploy these coatings after the 3+ year manufacturing process for 30-cm coatings.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.

2015年，美国国家科学基金会的激光干涉仪引力波天文台（LIGO）首次直接探测到引力波，开启了引力波天文学领域。LIGO探测引力波，即时空中的涟漪，使用的是一个“L”型探测器，即干涉仪，其臂长4公里。引力波在臂上引起微小的拉伸，这是通过在每条臂末端反射激光并比较反射光束来测量的。LIGO灵敏度的主要限制之一是镜面由于热激振动而移动。这些振动被称为热噪声，它们掩盖了引力波信号。该研究项目将通过使用由晶体半导体材料层形成的镜面涂层来研究减少这种“涂层热噪声”的方法。初步测量表明，这种结晶涂层将涂层热噪声降低十倍。因此，LIGO将能够看到宇宙中更远的几倍，观测黑洞和中子星的速度将大幅提高。这种快速增长的观测目录将为我们宇宙的组成、形成和演化的当前模型提供信息。回答关于宇宙的基本问题是激发、团结和激励全人类的思想。该研究计划的重点是继续开发GaAs/AlGaAs晶体涂层，用于LIGO探测器的下一次重大升级。除了具有优异的光学性能（散射10 ppm，吸收1 ppm）外，这些涂层还具有极低的弹性损失。晶体GaAs/AlGaAs涂层热噪声（CTN）的主要来源是热光噪声（TO），它是热弹性噪声（TE）和热折射噪声（TR）的组合。使用TO优化，可以调整涂层厚度，从而消除TE和TR效应。这些to优化涂层的CTN比目前的LIGO涂层低10倍。虽然这些结果非常令人鼓舞，但要在LIGO反射镜中实现这些成果，还有大量的工作要做。迄今为止，这些测量都是在小样本（≤75毫米）上进行的。该项目监督这些晶体涂层的发展，使其直径达到20厘米，最终达到30厘米，这适用于LIGO。PI正在与LIGO实验室合作，以测试越来越大尺寸的表面均匀性和光学特性。PI正在与锡拉丘兹大学小组合作，测试可能的电光噪声，并开发一种使用2 μ m激光器的新型臂锁系统。PI正在开发涂层的有限元模型，以准确预测CTN。与此同时，他正在与麻省理工学院LIGO实验室小组合作，提高CTN实验的灵敏度，以便能够测量在GaAs/AlGaAs晶体涂层中观察到的低CTN。PI正与安柏瑞德大学、美国大学和斯坦福大学的同事合作，测试可能存在的双折射噪声。最后，PI正在探索可以利用目前可用的20厘米GaAs/AlGaAs涂层的干涉仪设计，而不是在30厘米涂层的制造过程中等待3年以上才能部署这些涂层。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。