Absolute and Differential Complex E Field Reconstruction by Phase Shifting Interferometry

The Habitable Worlds Observatory is expected to carry a coronagraph instrument capable of direct imaging of Earth-like exoplanets in the habitable zone of distant stars. Such an instrument requires stability of its wavefront to a few picometers RMS in phase, and ≪ 1% in amplitude over one observational cycle of approximately 12 hours. These tight requirements demand an adaptive optics system with extreme long term internal stability. In this paper, we show how phase shifting interferometry helps enable this long term stability by suppressing sources of 1/f noise while also providing measurement of both the phase and amplitude of the beam. Additionally, we show how a new type of noncommon path interferometer with a photonic phase shifter enables inclusion of this type of modulation into existing coronagraph layouts.