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Figure 1
Figure 1: Time-Delay Interferometry (TDI). LISA-like detectors measure GWs by transmitting laser light between three spacecraft in triangular configuration, and comparing the optical phase of the incident lasers against reference lasers on each spacecraft. To avoid extreme requirements on laser-frequency stability over the course of the many seconds required for transmission around the triangle, data analysts will generate time-delayed linear combinations of the phase comparisons; the combinations simulate nearly equal-delay optical paths around the sides of the triangle, and (much like an equal-arm Michelson interferometer) they suppress laser frequency noise. Many such combinations, including those depicted here, are possible, but altogether they comprise at most three independent gravitational-wave observables. Image reproduced by permission from [447], copyright by APS.