Design and implementation of an SLM-driven coherent differential imaging scheme

Abstract

Direct imaging of exoplanets from the ground remains fundamentally limited by fast-evolving post-adaptive optics (AO) residual wavefront errors, and by quasi-static speckles arising from non-common path aberrations (NCPAs) downstream of the AO wavefront sensor. To first order, both sources of contrast degradation remain coherent with the stellar light, and recent studies have shown that coherent differential imaging (CDI) techniques can address their quasi-static and slowly evolving components. Recent laboratory demonstrations using focal plane phase diversity with an active LCoS spatial light modulator (SLM) have further established that local phase modulation can distinguish coherent speckles from incoherent astrophysical signals. Here we present a framework for the design and implementation of an SLM-based CDI integrator. Through simulations, we study the effects of varying the number of phase steps, modulation ring width, planet separation, and planet-to-star contrast. The numerical results are further supported by an initial laboratory validation. In the future, with the emergence of ultra-low-noise fast near-infrared detectors such as avalanche photodiode and microwave kinetic inductance detector (MKID) arrays, time-domain focal-plane CDI detection schemes could potentially also be able to suppress rapidly varying post-AO residual wavefront errors.