RUI: Investigations of Mirror Thermal Noise for Gravitational Wave Detectors

RUI：引力波探测器镜面热噪声研究

• 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

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 (NSF) 的 LIGO（激光干涉引力波天文台）首次直接探测引力波，利用“L”形探测器（称为“L”形探测器）探测引力波，即时空涟漪。干涉仪，臂长 4 公里，引力波会在臂中产生微小的差异拉伸，这是通过末端镜子反射激光来测量的。 LIGO 灵敏度的主要限制之一是镜面因热引起的振动（称为热噪声）而移动，这些振动掩盖了引力波信号。一种通过使用由晶体半导体材料层形成的镜面涂层来减少这种“涂层热噪声”的方法，初步测量表明，这种晶体涂层将能够将涂层热噪声降低十倍。看在宇宙中更远的地方，观测黑洞和中子星的速度急剧增加，这一快速增长的观测目录将为当前宇宙的组成、形成和演化模型提供信息，回答有关宇宙的基本问题。宇宙是激发、团结和激励全人类的想法。该研究计划的重点是继续开发 GaAs/AlGaAs 晶体涂层，除了具有出色的光学性能外，还可以用于 LIGO 探测器的下一次重大升级。属性（散点10 ppm，吸收率 1 ppm），这些涂层表现出极低的弹性损耗，晶体 GaAs/AlGaAs 涂层热噪声 (CTN) 的主要来源是热光 (TO) 噪声，它是热弹性的组合。 (TE) 和热折射 (TR) 噪声通过 TO 优化，可以调整涂层厚度，从而消除 TE 和 TR 效应，这些 TO 优化涂层的噪声降低了 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，仍然需要做大量的工作。迄今为止，这些测量都是在小型（≤ 75 毫米）样品上进行的。该项目负责监督这些直径为 20 厘米并最终达到 30 厘米的晶体涂层的开发，这些涂层适用于 LIGO。PI 正在与 LIGO 实验室合作，测试尺寸不断增加的表面均匀性和光学特性。 PI 与雪城大学小组合作测试可能的电光噪声并开发使用 2 µm 激光器的新型臂锁定系统，以并行准确预测 CTN。正在与麻省理工学院 LIGO 实验室小组合作，提高其 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 正在与同事合作。最后，PI 正在探索可以利用当前可用的 20 厘米 GaAs/AlGaAs 涂层的干涉仪设计，而不是等待在 3 年多的制造过程后部署这些涂层。 30 厘米涂层。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors

用于引力波探测器的衬底转移 GaAs/AlGaAs 晶体涂层

• DOI: 10.1063/5.0140663
• 发表时间: 2023-03
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Cole, G. D.;Ballmer, S. W.;Billingsley, G.;Cataño;Fejer, M.;Fritschel, P.;Gretarsson, A. M.;Harry, G. M.;Kedar, D.;Legero, T.;et al
• 通讯作者: et al