Evolved Laser Interferometer Space Antenna

View of amplified effects of a + polarized gravitational wave (stylized) on eLISA laser beams / arms paths.
Detector noise curves for LISA and eLISA as a function of frequency. They lie in between the bands for ground-based detectors like Advanced LIGO (aLIGO) and pulsar timing arrays such as the European Pulsar Timing Array (EPTA). The characteristic strain of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve.[27]

Simplified operation of a gravitational wave observatory

Figure 1: A beamsplitter (green line) splits coherent light (from the white box) into two beams which reflect off the mirrors (cyan oblongs); only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected (purple circle).
Figure 2: A gravitational wave passing over the left arm (yellow) changes its length and thus the interference pattern.

Like every modern gravitational wave observatory, eLISA is based on laser interferometry technique. Its three satellites form a giant Michelson interferometer in which two “slave” satellites play the role of reflectors and one “master” satellite the one of source and observer. While a gravitational wave is passing through the interferometer, lengths of the two eLISA arms are varying due to space-time distortions resulting from the wave. Practically, it measures a relative phase shift between one local laser and one distant laser by light interference. Comparison between the observed laser beam frequency (in return beam) and the local laser beam frequency (sent beam) encodes the wave parameters. See: Evolved Laser Interferometer Space Antenna

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