KAGRA引力波探测器中蓝宝石测试镜光学性质研究

1. 武汉大学物理科学与技术学院 武汉 430072;2. College of Science Department of Physics, Rikkyo University, Tokyo 171-8501;3. National Astronomical Observatory of Japan, Tokyo 181-8588

P142;

Optical Characterization of Sapphire Test Mirror in KAGRA Gravitational Wave Detector
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1.School of Physics and Technology, Wuhan University, Wuhan 430072;2.College of Science Department of Physics, Rikkyo University, Tokyo 171-8501;3.National Astronomical Observatory of Japan, Tokyo 181-8588

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摘要:

低温制冷技术是下一代激光干涉仪引力波探测器的核心技术之一. 日本引力波探测器KAGRA (Kamioka Gravitational Wave Detector)作为该技术的前沿开拓者, 将运行在20K的超低温环境中, 并使用在低温下热噪声较低的单晶蓝宝石晶体作为测试镜. 然而, 高质量大尺寸低吸收率的蓝宝石晶体极难制备. 此外, 由于蓝宝石晶体存在晶格结构不均匀, 很容易导致不必要的双折射效应, 从而影响探测器的目标灵敏度. 基于上述问题, 开发了两套大尺寸光学测量系统, 首次系统研究了KAGRA低温蓝宝石测试镜的光学特性. 首先, 根据探测器对测试镜热噪声的要求, 开发了一套基于光热共光路干涉技术的光学测量系统, 该系统可对测试镜以及测试镜表面涂层的光学吸收进行有效的表征. 其次, 基于光学吸收测量系统, 开发了一套双折射效应测量系统, 该系统可以有效表征测试镜中双折射的均匀性. 目前两套测量系统的搭建与调试已完成, 对蓝宝石测试镜光学吸收的测量灵敏度达到了1.5ppm/cm, 双折射测量系统的空间分辨率小于0.3mm times 0.3mm. 该工作对降低大尺寸低温测试镜双折射效应及提高探测器灵敏度具有重要意义.

Abstract:

Cryogenic technology is one of the key technologies for the next generation of Laser Interferometer Gravitational-Wave detector. The Japanese gravitational wave interferometer KAGRA (Kamioka Gravitational Wave Detector), as the pathfinder of this technology, will operate in a 20 K cryogenic environment and use a sapphire single crystal with less thermal noise at low temperatures as the test mirror. However, sapphire crystals with high quality, large size, and low absorption rate are extremely difficult in manufacturing. In addition, due to the inhomogeneity of lattice structure in the sapphire crystal, it is easy to cause unnecessary birefringence effects, thereby affecting the target sensitivity of the detector. Based on the above problems, this paper developed two large-size optical measurement systems, and for the first time studied the optical characteristics of KAGRA cryogenic sapphire test mirrors systematically. First of all, according to the requirements of the detector for the thermal noise of the test mirror, we developed an optical measurement system based on the photothermal common-path interferometer technique, which can characterize the optical absorption of the test mirror and the surface coating of the test mirror effectively. Secondly, based on the optical absorption measurement system, we developed the birefringence effect measurement system, which can characterize the uniformity of birefringence in the test mirror. At present, the construction and testing of these two measurement systems have been completed, and the measurement sensitivity of the optical absorption of the sapphire test mirror has reached 1.5ppm/cm. As for the birefringence measurement system, its spatial resolution is less than 0.3mm $\times$ 0.3mm. This work is of high significance for reducing the birefringence effect of large-size cryogenic test mirrors and improving the sensitivity of the detector.

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##### 历史
• 收稿日期:2021-03-11
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• 在线发布日期: 2021-12-07
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