High contrast vacuum nuller testbed (VNT) contrast, performance, and null control

Abstract

WORD ABSTRACTHerein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. The VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. ABSTRACTHerein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. Tbe VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. We discuss the development of the vacuum Visible Nulling Coronagraph testbed (VNT). The VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10', 10" and ideally 10 10 at an inner working angle of 2*AID. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the laboratory results, optical configruation, critical technologies !II1d the null sensing and control approach.

The AFTA coronagraph instrument

“…At the present time five candidate coronagraph approaches are being studied for use in the mission. The coronagraph layout discussed below, can, with minor modifications, support all but the visible nulling coronagraph (VNC) 6 which has a two-stage shearing nuller, a segmented deformable mirror, and a spatial filter array consisting of lenslets and single mode fiber optics or an integrated optics array. 11 The Lyot, Vector Vortex, PIAA, and shaped pupil coronagraphs use continuous face sheet deformable mirrors (DMs).…”

“…While this pupil considerably complicates the design of a highcontrast coronagraph, several promising approaches have emerged that are expected to enable detection of 10 -9 contrast objects to within the 3 rd Airy ring of the point spread function in broad-band light. [2][3][4][5][6] The design reference mission places the telescope in an inclined geosynchronous orbit where future commercial robotic servicing capabilities may allow replacement/upgrade of the science instruments and key spacecraft components. For this reason, the instruments will be installed on a radial rail system within a multi-bay instrument carrier structure behind the primary mirror.…”

MEMS Deformable Mirrors for Space-Based High-Contrast Imaging

“…A 32 × 32 actuator BMC MEMS DM was used in vacuum to create a dark hole with 10-7 contrast with polychromatic light for the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) mission concept study [85,86]. The Visible Nulling Coronagraph (VNC) testbed used an Iris-AO DM with 169 hexagonal segments to demonstrate a dark hole with 10-9 contrast in vacuum [87].…”

The Segmented Aperture Interferometric Nulling Testbed (SAINT) I: overview and air-side system description

“…Evaluations of segmented apertures, sensing/control, and telescope stability show that the VNC leads to a viable and manageable approach for a flight mission, 14,15 including the discovery mission proposal for EPIC. 5 To further evaluate the approach and sub-system-level technologies, a VNC laboratory testbed was developed at GSFC that has achieved milestones in nulling coronagraphy.…”