Arm-length stabilisation for interferometric gravitational-wave   detectors using frequency-doubled auxiliary lasers
  Residual motion of the arm cavity mirrors is expected to prove one of the principal impediments to systematic lock acquisition in advanced gravitational-wave interferometers. We present a technique which overcomes this problem by employing auxiliary lasers at twice the fundamental measurement frequency to pre-stabilise the arm cavities' lengths. Applying this approach, we reduce the apparent length noise of a 1.3 m long, independently suspended Fabry-Perot cavity to 30 pm rms and successfully transfer longitudinal control of the system from the auxiliary laser to the measurement laser. 
Adam J. Mullavey, Bram J. J. Slagmolen, John Miller, Matthew Evans,   Peter Fritschel, Daniel Sigg, Sam J. Waldman, Daniel A...
physics.ins-det gr-qc