Equal-arm interferometric detectors of gravitational radiation allow phase measurements many orders of magnitude below the intrinsic phase stability of the laser injecting light into their arms. This is because the noise in the laser light is common to both arms, experiencing exactly the same delay, and thus cancels when it is differenced at the photo detector. In this situation, much lower level secondary noises then set the overall performance. If, however, the two arms have different lengths (as will necessarily be the case with space-borne interferometers), the laser noise experiences different delays in the two arms and will hence not directly cancel at the detector. In order to solve this problem, a technique involving heterodyne interferometry with unequal arm lengths and independent phase-difference readouts has been proposed. It relies on properly time-shifting and linearly combining independent Doppler measurements, and for this reason it has been called Time-Delay Interferometry (TDI). This article provides an overview of the theory and mathematical foundations of TDI as it will be implemented by the forthcoming space-based interferometers such as the Laser Interferometer Space Antenna (LISA) mission. We have purposely left out from this first version of our "Living Review" article on TDI all the results of more practical and experimental nature, as well as all the aspects of TDI that the data analysts will need to account for when analyzing the LISA TDI data combinations. Our forthcoming "second edition" of this review paper will include these topics.

中文翻译：

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时延干涉测量。


引力辐射的等臂干涉探测器允许进行比将光注入其臂的激光的固有相位稳定性低多个数量级的相位测量。这是因为激光中的噪声对于两个臂来说是共同的，经历完全相同的延迟，因此当它在光电探测器处存在差异时就被抵消。在这种情况下，低得多的二次噪声会决定整体性能。然而，如果两个臂具有不同的长度（星载干涉仪必然会出现这种情况），则激光噪声在两个臂中经历不同的延迟，因此不会在探测器处直接抵消。为了解决这个问题，提出了一种涉及不等臂长和独立相位差读数的外差干涉测量技术。它依赖于正确的时移和线性组合独立的多普勒测量，因此它被称为时延干涉测量（TDI）。本文概述了 TDI 的理论和数学基础，因为它将由即将推出的天基干涉仪（例如激光干涉仪空间天线 (LISA) 任务）来实现。我们特意从有关 TDI 的“生活评论”文章的第一个版本中省略了所有更具实践性和实验性的结果，以及数据分析师在分析 LISA TDI 时需要考虑的 TDI 的所有方面数据组合。我们即将发表的这篇综述论文的“第二版”将包括这些主题。