LISA laser noise cancellation test using time-delayed interferometry

ABSTRACT The Laser-Interferometer-Space-Antenna (LISA) is a space-based interferometer with arm lengths of 5*10 9 m. Its designgoal is to measure gravitational waves with a strain sensitivity of 10 -23 at 10 mHz (for SNR=5 and 1 year integration).Unlike in earth-based interferometers the arm lengths can differ by up to 2% or 10 8 m. For that reason frequency noise inthe ~1 m laser will not cancel in the direct interference signal. A laser locked to a ULE reference cavity (CTE~3*10 -8 / o K) in a 1 o K/ Hz environment will have about 10 Hz/ Hz frequency noise. The LISA sensitivity goal requires for thelaser noise of less than 10 -5 Hz/ Hz, about a factor 10 -6 below what has been achieved (1) . Cancellation of laser frequencynoise can be achieved by time-delayed-interferometry (TDI) (2,3) . We describe a laboratory test of TDI with an unequalarm interferometer. The intent is to ascertain the performance limitations and proof-of-concept for 6 orders of magnitudefrequency noise suppression.Keywords: LISA, time-delayed interferometry, gravitational wave detector, laser frequency stability