RUI: Investigations of Mirror Coatings for A+ and Third Generation Gravitational Wave Detectors

RUI：第一代和第三代引力波探测器镜面涂层的研究

基本信息

批准号：
1912699
负责人：
Steven Penn
金额：
$ 24万
依托单位：
Hobart and William Smith Colleges
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-08-01 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1912699&HistoricalAwards=false
关键词：
RUI Investigations Mirror Coatings A+

项目摘要

This award supports research in gravitational wave detector instrumentation and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. The Laser Interferometer Gravitational-wave Observatory (LIGO) project has opened new windows to observe and understand the universe. The first direct detection of gravitational waves was also the first observation of the inspiral and merger of binary black holes. While black hole mergers are one of the most energetic events in the universe, they were not visible by electromagnetic telescopes. Now, after viewing several such observations, LIGO is developing a catalogue of the population of binary black hole systems. In addition, LIGO's observation of a binary neutron star merger inaugerated the field of multi-messenger astronomy. These simultaneous observations of gravitational waves and light allow for deeper insights into neutron star structure, and they allow us to test fundamental concepts like the speed of gravitational waves and the Hubble constant. The major challenges in this field are the noise sources that limit sensitivity, most notably thermal noise in LIGO's mirror coatings. LIGO is an interferometer, an L-shaped detector with 4 km long arms, which detects gravitational waves by observing tiny differential stretching in the arms. Identical light waves, emitted at the vertex, pass down each arm to a mirror and are reflected back. Any phase difference in the recombining beams corresponds to a difference in arm length. Thus detecting gravitational waves depends on the precision detection of the surface of the end mirrors, but for LIGO that precision is a daunting one billionth of an atom width. The mirrors, at room temperature (300; K), vibrate due to thermal energy at the mirror's resonant frequencies, which are much higher than the gravitational waves frequencies that LIGO can detect. If the mirrors were composed of an ideal elastic material, these vibrations could be ignored and of no concern. Indeed the fused silica glass used for the mirror substrates is a nearly ideal elastic material. However the highly reflective mirror coatings have internal friction that shifts some of the vibrational energy down to gravitational wave frequencies. That motion, which masks the gravitational wave signal, is mirror coating thermal noise (CTN). This research project is designed to understand and reduce CTN in order to improve LIGO's sensitivity. This project aims to reduce coating thermal noise by lowering the dissipation, or mechanical loss, in the coating materials. This dissipation occurs when a fluctuation in thermal or strain energy causes a dissipative state transition. This dissipative process is commonly modeled as an asymmetric double-well potential. The dissipation is reduced by increasing the energy asymmetry in the states, which lowers the transition probability. The team will investigate crystalline coatings, specifically AlGaAs, which has excellent optical properties. The AlGaAs elastic loss is very low for small samples, but further study is needed to understand the loss for large coatings. The team will also investigate stabilized amorphous dielectric coatings. Amorphous dielectric coatings produced by ion beam sputtering can have excellent optical properties, but they typically have high elastic loss. Annealing lowers the dissipation by allowing the material to relax into its lowest energy state. But annealing is limited by low crystallization temperature for these materials. Stabilized amorphous coatings are mixtures of dielectrics in which material mixture frustrates crystallization and allows a higher annealing temperature and lower elastic loss. The team will collaborate on experiments to test if the effects of annealing can be achieved by heating the substrate during deposition.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.

该奖项支持引力波探测器仪器的研究，并解决了美国国家科学基金会“宇宙之窗”大构想的优先领域。激光干涉仪引力波天文台（LIGO）项目为观察和理解宇宙打开了新的窗口。首次直接探测到引力波，也是首次观测到双黑洞的吸气和并合。虽然黑洞合并是宇宙中最具能量的事件之一，但电磁望远镜无法观测到它们。现在，在查看了几次此类观测结果后，LIGO 正在开发双黑洞系统总体目录。此外，LIGO 对双中子星合并的观测开创了多信使天文学领域。对引力波和光的同时观测可以让我们更深入地了解中子星结构，并使我们能够测试引力波速度和哈勃常数等基本概念。该领域的主要挑战是限制灵敏度的噪声源，尤其是 LIGO 镜面涂层中的热噪声。 LIGO 是一种干涉仪，是一个具有 4 公里长臂的 L 形探测器，通过观察臂中微小的差异拉伸来探测引力波。从顶点发出的相同光波沿着每条臂传递到镜子并反射回来。重组光束中的任何相位差都对应于臂长的差异。因此，探测引力波取决于端镜表面的精确探测，但对于 LIGO 来说，其精确度是令人畏惧的原子宽度的十亿分之一。在室温 (300; K) 下，镜子会因镜子谐振频率的热能而振动，该频率远高于 LIGO 可以检测到的引力波频率。如果镜子是由理想的弹性材料制成的，那么这些振动就可以忽略不计，无需担心。事实上，用于镜子基底的熔融石英玻璃是一种近乎理想的弹性材料。然而，高反射镜涂层具有内部摩擦，可将部分振动能量降低至引力波频率。这种掩盖引力波信号的运动就是镜面涂层热噪声（CTN）。该研究项目旨在了解和减少 CTN，以提高 LIGO 的灵敏度。该项目旨在通过降低涂层材料的耗散或机械损失来减少涂层热噪声。当热能或应变能的波动导致耗散态转变时，就会发生这种耗散。这种耗散过程通常被建模为不对称双阱势。通过增加状态中的能量不对称性来减少耗散，从而降低跃迁概率。该团队将研究结晶涂层，特别是具有优异光学性能的 AlGaAs。对于小样品来说，AlGaAs 弹性损失非常低，但需要进一步研究来了解大涂层的损失。该团队还将研究稳定的非晶介电涂层。通过离子束溅射生产的非晶介电涂层具有优异的光学性能，但它们通常具有较高的弹性损耗。退火通过使材料松弛到最低能量状态来降低耗散。但退火受到这些材料的低结晶温度的限制。稳定的非晶涂层是电介质的混合物，其中材料混合物抑制结晶并允许更高的退火温度和更低的弹性损失。该团队将合作进行实验，以测试是否可以通过在沉积过程中加热基板来实现退火的效果。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。