Progress toward space-based nulling interferometry: comparison of null stabilization approaches

Nulling interferometry is a technique, which can potentially enable the direct detection of light from planets orbiting around nearby stars. In this approach, the light from two or more telescopes is combined using achromatic destructive interference, so that the bright stellar signal incident along the optical axis is cancelled. The radiation from fainter off-axis sources is thus left more amenable to detection. Deep nulling of broadband thermal white light has now been demonstrated experimentally, and two different methods of stabilizing the interferometer at the null-fringe position have been successfully exploited. In this report, the two null-fringe stabilization approaches investigated in our experiments are compared on a theoretical basis, and laboratory results obtained with both stabilization approaches are presented. Finally, a brief status update on current performance levels is provided