LISA sensitivity training

JPL scientists verify measurement techniques required for space-based gravitational wave detectors

Geometry of the JPL interferometry testbed

In a breakthrough that has been years in the making, scientists at the Jet Propulsion Laboratory (JPL) have completed the first experimental verification of phase measurement and interferometer techniques needed for space-based gravitational wave detectors. The experiment is described by Glenn de Vine and others in "Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna," published in Physical Review Letters (paywall), discussed in Physics Today (paywall), and highlighted in APS Physics (open access).

Space-based gravitational-wave detectors will give birth to an entirely new field, gravitational-wave astronomy. The first such detector, the Laser Interferometer Space Antenna (LISA), is planned as a joint mission between Europe (European Space Agency) and the U.S.A. (National Aeronautics and Space Administration) for launch in the early 2020s. LISA will consist of three spacecraft separated by 5 million km. The constellation will respond to passing gravitational waves from sources throughout the Universe, such as black-hole collisions, with slight changes in the armlengths. Lasers linking the spacecraft will respond to these motions, which are as small as 5 picometers (1pm = 1 millionth of a millionth of a meter). An interferometric measurement system is required to measure these small motions, which appear as phase changes in the laser light sent from the very distant other spacecraft.

The required sensitivity was achieved at JPL in a configuration that contains the essential features of LISA interferometry, but on a laboratory scale. De Vine et al. were able to simultaneously suppress two sources of technical noise that would otherwise ruin the measurement by many orders of magnitude: phase fluctuations in the clocks used to synchronize the measurements, and frequency fluctuations in the lasers. The total noise suppression achieved was 9 orders of magnitude (or a factor of 1000 million). The results provide validation of the LISA phasemeter and of the essential features of the LISA optical design, as well as evidence that LISA performance will not be limited by technical phase noise.