Phase Reconfigurable Nulling Interferometer

We propose the use of a phase reconfigurable spatial light modulator (SLM) in place of a static computer generated hologram (CGH) in interferometric test systems for next generation meter class telescope optics. A liquid crystal on silicon (LCoS) SLM offers additional flexibility, potentially higher measurement precision, and relaxed alignment requirements over static CGHs. Programmable phase provides the user with the ability to test different optical components without requiring the design of a different CGH in each case. Applying the phase to the SLM in-situ, to generate the optical null, greatly relaxes the requirements for the critical alignment precision associated with CGHs. Additional measurement precision may be achieved by applying additional piston phase changes to the SLM hologram in the manner of a vibration free phase shifting interferometer. Phase errors due to air currents could potentially be removed on the fly, and phase errors in other system components could also be compensated. Phase I examines a small format 512x512 10 bit SLM on a benchtop test interferometer to validate the concept using commercial off the shelf (COTS) components. A phase II continuation would implement a 31mm square large format 1536x1536 SLM with 768 waves of applicable phase stroke.