LISA laser noise cancellation test using time-delayed interferometry

The Laser-Interferometer-Space-Antenna (LISA) is a space-based interferometer with arm lengths of 5*10 9 m. Its design goal is to measure gravitational waves with a strain sensitivity of 10-23 at 10 mHz. Unlike in earth-based interferometers the arm lengths can differ by up to 2% or 108 m. For that reason frequency noise in the λ ~ 1 μm laser will not cancel in the direct interference signal. A laser locked to a ULE reference cavity in a 1°μK/square root Hz environment will have about 10 Hz/square root Hz frequency noise. The LISA sensitivity goal requires for the laser noise of less than 10-5 Hz/square root Hz, about a factor 10-6 below what has been achieved (1). Cancellation of laser frequency noise can be achieved by time-delayed-interferometry (TDI) (2,3). We describe a laboratory test of TDI with an unequal arm interferometer. The intent is to ascertain the performance limitations and proof-of-concept for 6 orders of magnitude frequency noise suppression.