从透射波前误差测量表征KAGRA蓝宝石镜子的双折射不均匀性
Characterisation of birefringence inhomogeneity of KAGRA sapphire mirrors from transmitted wavefront error measurements
AI总结：
本文提出一种基于菲佐干涉仪透射波前误差测量的快速双折射表征方法，成功重建KAGRA直径22厘米蓝宝石测试质量的双折射不均匀性，并验证了其对光束形状的影响，为未来更大尺寸低温测试质量的双折射表征提供了关键技术。
摘要：
将测试质量冷却至低温是降低引力波探测器热噪声的一种方法。晶体材料因其在低温下优异的热学和光学性能，被认为是制造低温测试质量及其镀膜的最有前景的材料。然而，由于晶体中的局部杂质和不均匀性所导致的双折射可能会降低探测器的性能。因此，在二维区域内进行双折射测量或成像显得尤为重要。本研究描述了一种对大尺寸样品进行快速双折射测量的方法，该方法仅需将使用线偏振光的菲佐干涉仪进行的一系列透射波前误差测量简单组合即可实现。利用该方法，完整重建了KAGRA两个直径为22厘米的输入测试质量的双折射不均匀性信息。随后，利用这些双折射信息计算了光场在通过基底时正交偏振方向上的横向光束形状。计算结果能够找到与使用KAGRA干涉仪进行的原位测量一致的光束形状。这项技术对于未来探测器中测试质量的双折射表征至关重要，因为未来探测器将使用更大尺寸的测试质量。
英文摘要：
Cooling down test masses to cryogenic temperatures is a way to reduce the thermal noise of gravitational wave detectors. Crystalline materials are considered the most promising materials for fabricating cryogenic test masses and their coatings because of their excellent thermal and optical properties at low temperatures. However, birefringence owing to local impurities and inhomogeneities in the crystal can degrade the performance of the detector. The birefringence measurement or mapping over a two-dimensional area is thus important. This study describes a method for fast birefringence measurements of a large sample by simply combining a series of transmission wavefront error measurements using linearly polarised light with Fizeau interferometers. Using this method, the birefringence inhomogeneity information of KAGRA's two input test masses with a diameter of 22 cm was fully reconstructed. The birefringence information was then used to calculate the transverse beam shapes of the light fields in orthogonal polarisation directions when passing through the substrate. It was possible to find a calculated beam shape consistent with in-situ measurements using the KAGRA interferometer. This technique is crucial for birefringence characterisation of test masses in future detectors, where even larger sizes are used.
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