The Roman Space Telescope will have the first advanced coronagraph in space, with deformable mirrors (DMs) for wavefront control (WFC), low-order wavefront sensing and maintenance, and a photon-counting detector. It is expected to be able to detect and characterize mature, giant exoplanets in reflected visible light. Over the past decade, the performance of the coronagraph in its flight environment has been simulated with increasingly detailed diffraction and structural/thermal finite-element modeling. With the instrument now being integrated in preparation for launch within the next few years, the present state of the end-to-end modeling, including the measured flight components such as DMs, is described. The coronagraphic modes, including characteristics most readily derived from modeling, are thoroughly described. The methods for diffraction propagation, WFC, and structural and thermal finite-element modeling are detailed. The techniques and procedures developed for the instrument will serve as a foundation for future coronagraphic missions, such as the Habitable Worlds Observatory.
The Roman Space Telescope will be launched in a few years, and its Coronagraphic Instrument (CGI) is being assembled after a decade of development. The on-orbit performance of CGI has been predicted using numerical modeling, including diffraction and wavefront control modeling to simulate images and finite element modeling to estimate wavefront instabilities due to thermal and vibrational (reaction wheels) disturbances. We describe the final end-to-end modeling results representing a realistic observing scenario.
Coronagraphic space telescopes for imaging Earth-like exoplanets, such as the projected Habitable Worlds Observatory, will require extraordinary optical stability, with wavefront drift performance measured in the picometers. This paper considers how active means, using sensing and control subsystems, can control the entire coronagraphic beam train, from the telescope’s segmented primary mirror, through the coronagraph’s deformable mirrors, to stabilize the electric field in the coronagraph. Integrated telescope and coronagraph models are used to show how this can work to preserve contrast at the 10-10 level and provide important observational efficiencies. In future work, the models will also be used to identify needed performance levels for the various control system components, to help inform NASA’s technology funding priorities.
Integrated optical models allow for accurate prediction of the as-built performance of an optical instrument. Optical models are typically composed of a separate ray trace and diffraction model to capture both the geometrical and physical regimes of light. These models are typically separated across both open-source and commercial software that don’t interface with each other directly. To bridge the gap between ray trace models and diffraction models, we have built an open-source optical analysis platform in Python called Poke that uses commercial ray tracing APIs and open-source physical optics engines to simultaneously model scalar wavefront error, diffraction, and polarization. Poke operates by storing ray data from a commercial ray tracing engine into a Python object, from which physical optics calculations can be made. We present an introduction to using Poke, and highlight the capabilities of two new propagation modules that add to the utility of existing scalar diffraction models. Gaussian Beamlet Decomposition is a ray-based approach to diffraction modeling that allows us to integrate physical optics models with ray trace models to directly capture the influence of ray aberrations in diffraction simulations. Polarization Ray Tracing is a ray-based method of vector field propagation that can diagnose the polarization aberrations in optical systems. Poke has been recently used to study the next generation of astronomical observatories, including the ground-based Extremely Large Telescopes (TMT, GMT, ELT) and a 6 meter space telescope (6MST) early concept for NASA’s Habitable Worlds Observatory.
Modern lenses offer high resolution and display a significant sensitivity to misalignment. Accurately detecting misalignment requires evaluation over the full field of view (FOV). We propose a method of utilizing commercial MTF test stations and custom software to measure, evaluate, and visualize the performance over this entire area. These techniques allow the detection and characterization of misaligned systems with greater accuracy than typical three or five field point MTF measurements.
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