Vol. 17 (2014) > lrr-2014-6

doi: 10.12942/lrr-2014-6
Living Rev. Relativity 17 (2014), 6

Time-Delay Interferometry

1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, U.S.A. and LIGO Laboratory, California Institute of Technology, Pasadena, CA 91125, U.S.A.
2 IUCAA, Post Bag 4, Ganeshkhind, Pune 411 007, India

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Article Abstract

Equal-arm 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, mathematical foundations, and experimental aspects associated with the implementation of TDI. Although emphasis on the application of TDI to the Laser Interferometer Space Antenna (LISA) mission appears throughout this article, TDI can be incorporated into the design of any future space-based mission aiming to search for gravitational waves via interferometric measurements. We have purposely left out all theoretical aspects that data analysts will need to account for when analyzing the TDI data combinations.

Keywords: Interferometry, Gravitational-wave detectors

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Since a Living Reviews in Relativity article may evolve over time, please cite the access <date>, which uniquely identifies the version of the article you are referring to:

Massimo Tinto and Sanjeev V. Dhurandhar,
"Time-Delay Interferometry",
Living Rev. Relativity 17,  (2014),  6. URL (cited on <date>):

Article History

ORIGINAL http://www.livingreviews.org/lrr-2005-4
Title Time-Delay Interferometry
Author Massimo Tinto / Sanjeev V. Dhurandhar
Date accepted 16 May 2005, published 15 July 2005
UPDATE http://www.livingreviews.org/lrr-2014-6
Title Time-Delay Interferometry
Author Massimo Tinto / Sanjeev V. Dhurandhar
Date accepted 28 July 2014, published 5 August 2014
Changes Major revision, updated and expanded. The number of references increased from 35 to 65. This revised version includes new and major theoretical and experimental results that have appeared in the literature since the original review got released. The new Section 5.3 covers recent work performed by S.V.D. and collaborators on the mathematical foundations of second-generation TDI. Section 5.4 instead addresses the derivation of the TDI space corresponding to a laser interferometer architecture with only two arms. This covers both the LISA mission in the eventuality of failure of one of its arms, or other mission concepts in which by design only two arms are envisioned. Finally, in Section 7 some practical and experimental aspects related to the performance specifications of the different subsystems used for implementing TDI have been included.
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