Methodological demonstration of laser beam pointing control for space gravitational wave detection missions

In space laser interferometer gravitational wave (G. W.) detection missions, the stability of the laser beam pointing direction has to be kept at 10 nrad/root Hz. Otherwise, the beam pointing jitter noise will dominate the noise budget and make the detection of G. W. impossible. Disturbed by the residue non-conservative forces, the fluctuation of the laser beam pointing direction could be a few mu rad/root Hz at frequencies from 0.1 mHz to 10 Hz. Therefore, the laser beam pointing control system is an essential requirement for those space G. W. detection missions. An on-ground test of such beam pointing control system is performed, where the Differential Wave-front Sensing technique is used to sense the beams pointing jitter. An active controlled steering mirror is employed to adjust the beam pointing direction to compensate the jitter. The experimental result shows that the pointing control system can be used for very large dynamic range up to 5 mu rad. At the interested frequencies of space G. W. detection missions, between 1 mHz and 1 Hz, beam pointing stability of 6 nrad/root Hz is achieved. (C) 2014 AIP Publishing LLC.