Nulling interferometric beam combiner utilizing dielectric plates: Experimental results in the visible broadband

A laboratory experiment was performed on the achromatic nulling in the visible to SIM requirements. The experiment employed phase shifting interferometry techniques on a spectrally-dispersed fringe to measure the phase as a function of wavelength. The phase was then used by a control system which adjusts the tilt of the plates and the air path difference until a satisfactory level of the null was achieved. A fast servo adjusted the air path difference to stabilize the phase to the nanometer level. The design issue and the experimental measure of phase versus wavelength are discussed. A description of the control system and a preliminary measure of the null are presented.