EAGER: Low Noise Cryogenic Optical Resonator

在实验物理前沿的几个领域的高精度测量今天受到布朗热波动的限制。这包括用于测量等效原理和引力平方反比定律的扭摆，宏观量子力学振荡器的研究，用于射电天文学脉冲星计时的低温蓝宝石振荡器，激光干涉仪引力波探测器的钟摆和镜子，以及原子钟和光谱学中的参考腔。例如，作为高级LIGO项目的一部分，目前正在美国建造的大型干涉仪将对来自剧烈天体物理现象的引力波具有前所未有的灵敏度，但由于光学涂层中的热噪声，其灵敏度受到限制。在未来，要想进一步显著改善引力波探测器的天体物理探测范围，就需要降低干涉仪反射镜中的热噪声。镜面的布朗运动也限制了现代稳定激光器的频率稳定性。这些激光被稳定在刚性的法布里-珀罗谐振腔中，反射镜与LIGO干涉仪中的反射镜非常相似。当今最好的原子钟受到用来检测它们的激光的频率波动的限制。提高光学腔的稳定性将使研究人员能够将原子钟的稳定性提高几个数量级。这项EAGER奖励支持初步研究，旨在通过首次尝试使用低温硅作为光学参考腔，将这些参考腔的线宽提高一个数量级以上。由于反射镜及其涂层中的热能与温度成正比，虽然这种腔内的噪声从未被测量过，但通过降低温度可以直接改善效果。所采用的方案未经测试，可能会发现意外的噪声源。然而，通过使用高质量的低温材料可以获得的潜在好处是巨大的，并且将对前沿物理测量产生深远的影响，可能是变革性的影响。超稳定的激光波长在引力波探测、原子钟和广义相对论测试等领域都是必不可少的工具。在这些领域中，激光波长的稳定性非常重要，因此激发了一个长期的研究计划，以构建越来越稳定的参考腔。除了了解低温下的热噪声行为外，这项研究最终可以为激光和原子钟的精度提供一个新的频率稳定性水平。

High precision measurements in several areas at the forefront of experimental physics today are limited by Brownian thermal fluctuations. This includes torsion pendulums used for measurements of the equivalence principle and the gravitational inverse-square law, investigations of macroscopic quantum mechanical oscillators, cryogenic sapphire oscillators for use in the timing of pulsars for radio astronomy, the pendulums and mirrors of laser interferometer gravitational wave detectors, and reference cavities in atomic clocks and spectroscopy. For example, the large scale interferometers which are now being built in the U.S. as part of the Advanced LIGO project, will have an unprecedented sensitivity to gravitational waves from violent astrophysical phenomena but are limited in their sensitivity by thermal noise in their optical coatings. In the future, making further dramatic improvements in the astrophysical reach of gravitational wave detectors will require reducing the thermal noise in the interferometers mirrors. This Brownian motion of the mirror surface also limits the achievable frequency stability of modern stabilized lasers. These lasers are stabilized to rigid Fabry-Perot resonator cavities with mirrors very similar to those in the LIGO interferometers. The best atomic clocks today are limited by the frequency fluctuations of the lasers used to interrogate them. Improving the stability of the optical cavities would allow researchers to push the stability of the atomic clocks by orders of magnitude.This EAGER award supports preliminary research aimed at making more than an order of magnitude improvement in the line-widths of these reference cavities by attempting to use, for the first time, cryogenic silicon as an optical reference cavity. Since the thermal energy in the mirrors and their coatings is proportional to temperature, there could be a direct improvement by going to low temperature although the noise in such a cavity has never been measured. The scheme to be used is untested and an unanticipated noise source may be uncovered. However, the potential benefits which can be reaped by using high quality, cryogenic materials are tremendous and would have far reaching, possibly transformative, repercussions in leading edge physics measurements.An ultra-stable laser wavelength is an essential tool in a variety of fields including gravitational-wave detection, atomic clocks, and tests of General Relativity. The stability of the laser wavelength is important enough in these fields to have stimulated a long program of research in constructing increasingly stable reference cavities. In addition to understanding the thermal noise behavior at low temperatures, this research could eventually produce a new level of frequency stability for lasers and precision for atomic clocks.