Kyle Van Gorkom

Modeling coronagraphic extreme wavefront control systems for high contrast imaging in ground and space telescope missions

The challenges of high contrast imaging (HCI) for detecting exoplanets for both ground and space applications can be met with extreme adaptive optics (ExAO), a high-order adaptive optics system that performs wavefront sensing (WFS) and correction at high speed. We describe 2 ExAO optical system designs, one each for ground- based telescopes and space-based missions, and examine them using the angular spectrum Fresnel propagation module within the Physical Optics Propagation in Python (POPPY) package. We present an end-to-end (E2E) simulation of the MagAO-X instrument, an ExAO system capable of delivering 6x10-5 visible-light raw contrast for static, noncommon path aberrations without atmosphere. We present an E2E simulation of a laser guidestar (LGS) companion spacecraft testbed demonstration, which uses a remote beacon to increase the signal available for WFS and control of the primary aperture segments of a future large space telescope, providing of order 10 factor improvement for relaxing observatory stability requirements.

MagAO-X: project status and first laboratory results

MagAO-X is an entirely new extreme adaptive optics system for the Magellan Clay 6.5 m telescope, funded by the NSF MRI program starting in Sep 2016. The key science goal of MagAO-X is high-contrast imaging of accreting protoplanets at Hα. With 2040 actuators operating at up to 3630 Hz, MagAO-X will deliver high Strehls (> 70%), high resolution (19 mas), and high contrast (< 1 × 10-4 ) at Hα (656 nm). We present an overview of the MagAO-X system, review the system design, and discuss the current project status.

Focal plane wavefront sensing and control strategies for high-contrast imaging on the MagAO-X instrument

The Magellan extreme adaptive optics (MagAO-X) instrument is a new extreme adaptive optics (ExAO) system designed for operation in the visible to near-IR which will deliver high contrast-imaging capabilities. The main AO system will be driven by a pyramid wavefront sensor (PyWFS); however, to mitigate the impact of quasi-static and non-common path (NCP) aberrations, focal plane wavefront sensing (FPWFS) in the form of low-order wavefront sensing (LOWFS) and spatial linear dark field control (LDFC) will be employed behind a vector apodizing phase plate (vAPP) coronagraph using rejected starlight at an intermediate focal plane. These techniques will allow for continuous high-contrast imaging performance at the raw contrast level delivered by the vAPP coronagraph ( 6 x 10-5). We present simulation results for LOWFS and spatial LDFC with a vAPP coronagraph, as well as laboratory results for both algorithms implemented with a vAPP coronagraph at the University of Arizona Extreme Wavefront Control Lab.

Characterization of deformable mirrors for the MagAO-X project

The MagAO-X instrument is an upgrade of the Magellan AO system that will introduce extreme adaptive optics capabilities for high-contrast imaging at visible and near-infrared wavelengths. A central component of this system is a 2040-actuator microelectromechanical (MEMS) deformable mirror (DM) from Boston Micromachines Corp. (BMC) that will operate at 3.63 kHz for high-order wavefront control. Two additional DMs from ALPAO will perform low-order and non-common-path science-arm wavefront correction. The accuracy of the wavefront correction is limited by our ability to command these DMs to a desired shape, which requires a careful characterization of each DM surface. We have developed a characterization pipeline that uses a Zygo Verifire Interferometer to measure the surface response and a Karhunen-Loeve transform to remove noise from our measurements. We present our progress in the characterization process and the results of our pipeline applied to an ALPAO DM97 and a BMC Kilo-DM, demonstrating the ability to drive the DMs to a flat of ≤2nm and ≤4nm RMS in our beam footprint on the University of Arizona Wavefront Control (UAWFC) testbed.

Design of the MagAO-X pyramid wavefront sensor

Adaptive optics systems correct atmospheric turbulence in real time. Most adaptive optics systems used routinely correct in the near infrared, at wavelengths greater than 1 μm. MagAO- X is a new extreme adaptive optics (ExAO) instrument that will offer corrections at visible-to- near-IR wavelengths. MagAO-X will achieve Strehl ratios of ≥70% at Hα when running the 2040 actuator deformable mirror at 3.6 kHz. A visible pyramid wavefront sensor (PWFS) optimized for sensing at 600-1000 nm wavelengths will provide the high-order wavefront sensing on MagAO-X. We present the optical design and predicted performance of the MagAO-X pyramid wavefront sensor.

Updated optical modeling of JWST coronagraph performance contrast, stability, and strategies

We update performance simulations and contrast predictions for JWSTs coronagraphs based on the latest infor- mation on the as-built telescope and instrument properties, including both static and dynamic contributions to wavefront error. By combining optical modeling of the telescope, instruments and coronagraph optics along with STScIs rigorously-validated exposure time calculation engine, we develop updated contrast models including contributions from effects such as target acquisition residuals, stellar color differences, etc. We present assessments of the impact of wavefront error changes over time between science and PSF reference stars, using modeled wavefront drifts on various timescales based on available observatory structural/thermal/optical modeling and tested performance during the OTIS cryo test, extrapolated to on-orbit conditions. For NIRCam we explore tradeoffs between different occulting masks at a given wavelength. Between now and the start of Cycle 1 science, these and other updated simulations will enable the science community to prepare analysis tools and PSF subtraction software to hit the ground running with JWST coronagraphic observations.

Making good use of JWST's coronagraphs: tools and strategies from a user's perspective

The James Webb Space Telescope (JWST) and its suite of instruments, modes and high contrast capabilities will enable imaging and characterization of faint and dusty astrophysical sources1-3 (exoplanets, proto-planetary and debris disks, dust shells, etc.) in the vicinity of hosts (stars of all sorts, active galactic nuclei, etc.) with an unprecedented combination of sensitivity and angular resolution at wavelengths beyond 2 μm. Two of its four instruments, NIRCam4, 5 and MIRI,6 feature coronagraphs7, 8 for wavelengths from 2 to 23 μm. JWST will stretch the current parameter space (contrast at a given separation) towards the infrared with respect to the Hubble Space Telescope (HST) and in sensitivity with respect to what is currently achievable from the ground with the best adaptive optics (AO) facilities. The Coronagraphs Working Group at the Space Telescope Science Institute (STScI) along with the Instruments Teams and internal/external partners coordinates efforts to provide the community with the best possible preparation tools, documentation, pipelines, etc. Here we give an update on user support and operational aspects related to coronagraphy. We aim at demonstrating an end to end observing strategy and data management chain for a few science use cases involving coronagraphs. This includes the choice of instrument modes as well as the observing and point-spread function (PSF) subtraction strategies (e.g. visibility, reference stars selection tools, small grid dithers), the design of the proposal with the Exposure Time Calculator (ETC), and the Astronomers Proposal Tool (APT), the generation of realistic simulated data at small working angles and the generation of high level, science-grade data products enabling calibration and state of the art data-processing.

JWST Optical Telescope Element Center of Curvature Test

The James Webb Space Telescope (JWST) Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM) completed their element level integration and test programs and were integrated to the next level of assembly called OTE/ISIM (OTIS) at Goddard Space Flight Center (GSFC) in Greenbelt, Maryland in 2016. Before shipping the OTIS to Johnson Space Center (JSC) for optical test at cryogenic temperature a series of vibration and acoustic tests were performed. To help ensure that the OTIS was ready to be shipped to JSC an optical center of curvature (CoC) test was performed to measure changes in the mirror’s optical performance to verify that the telescope’s primary mirror was not adversely impacted by the environmental testing and also help us in understanding potential anomalies identified during the JSC tests. The 6.5 meter diameter primary mirror consists of 18 individual hexagonal segments. Each segment is an off-axis asphere. There are a total of three prescriptions repeated six times each. As part of the CoC test each segment was individually measured using a high-speed interferometer (HSI) designed and built specifically for this test. This interferometer is capable of characterizing both static and dynamic characteristics of the mirrors. The latter capability was used, with the aid of a vibration stinger applying a low-level input force, to measure the dynamic characteristic changes of the PM backplane structure. This paper describes the CoC test setup and both static and dynamic test results.

JWST center of curvature test method and results

The James Webb Space Telescope (JWST) recently saw the completion of the assembly process for the Optical Telescope Element and Integrated Science Instrument Module (OTIS). This integration effort was performed at Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. In conjunction with this assembly process a series of vibration and acoustic tests were performed. To help assure the telescope’s primary mirror was not adversely impacted by this environmental testing an optical center of curvature (CoC) test was performed to measure changes in the mirror’s optical performance. The primary is a 6.5 meter diameter mirror consisting of 18 individual hexagonal segments. Each segment is an off-axis asphere. There are a total of three prescriptions repeated six times each. As part of the CoC test each segment was individually measured using a high-speed interferometer (HSI) designed and built specifically for this test. This interferometer is capable of characterizing both static and dynamic characteristics of the mirrors. The latter capability was used, with the aid of a vibration stinger applying a low-level input force, to measure the dynamic characteristic changes of the PM backplane structure. This paper describes the CoC test setup, an innovative alignment method, and both static and dynamic test results.