Review of high-contrast imaging systems for current and future ground- and space-based telescopes I: coronagraph design methods and optical performance metrics

Mawet

et al. 2019

Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber,"Abstract. Linking a coronagraph instrument to a spectrograph via a single-mode optical fiber is a pathway toward detailed characterization of exoplanet atmospheres with current and future ground-and space-based telescopes. However, given the extreme brightness ratio and small angular separation between planets and their host stars, the planet signal-to-noise ratio will likely be limited by the unwanted coupling of starlight into the fiber. To address this issue, we utilize a wavefront control loop and a deformable mirror to systematically reject starlight from the fiber by measuring what is transmitted through the fiber. The wavefront control algorithm is based on the formalism of electric field conjugation (EFC), which in our case accounts for the spatial mode selectivity of the fiber. This is achieved by using a control output that is the overlap integral of the electric field with the fundamental mode of a single-mode fiber. This quantity can be estimated by pairwise image plane probes injected using a deformable mirror. We present simulation and laboratory results that demonstrate our approach offers a significant improvement in starlight suppression through the fiber relative to a conventional EFC controller. With our experimental setup, which provides an initial normalized intensity of 3 × 10 −4 in the fiber at an angular separation of 4λ∕D, we obtain a final normalized intensity of 3 × 10 −6 in monochromatic light at λ ¼ 635 nm through the fiber (100× suppression factor) and 2 × 10 −5 in Δλ∕λ ¼ 8% broadband light about λ ¼ 625 nm (10× suppression factor). The fiber-based approach improves the sensitivity of spectral measurements at high contrast and may serve as an integral part of future space-based exoplanet imaging missions as well as ground-based instruments.

Section: Perspectivesmentioning

confidence: 99%

Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber

Sayson

Mawet

et al. 2019

“…where E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 1 3 ; 1 1 6 ; 6 6 6 FTfEðx; yÞg ¼ 1 λf ZZ Eðx; yÞe −ikðxξþyηÞ∕f dx dy; (13) k ¼ 2π∕λ, λ is the wavelength, f is the focal length, and Lðx; yÞ is the LS function. Here the LS is a simple circular aperture that is undersized with respect to the geometric beam.…”

Section: Discussionmentioning

confidence: 99%

“…The raw contrast at a given position is defined as the ratio between the intensity due to an on-axis source (the star) and an equivalent source at that position. 13 The normalized intensityÎðξ; ηÞ is divided by the intensity of an off-axis source at a representative position in the image. In the following, we assume that the DM is nominally in the state that creates a dark hole in the image, which minimizes the normalized intensity.…”

Section: Theorymentioning

confidence: 99%

Microelectromechanical deformable mirror development for high-contrast imaging, part 2: the impact of quantization errors on coronagraph image contrast

Echeverri

Bendek

et al. 2020

Stellar coronagraphs rely on deformable mirrors (DMs) to correct wavefront errors and create high-contrast images. Imperfect control of the DM limits the achievable contrast, and therefore, the DM control electronics must provide fine surface height resolution and low noise. We study the impact of quantization errors due to the DM electronics on the image contrast using experimental data from the High Contrast Imaging Testbed facility at NASA's Jet Propulsion Laboratory. We find that the simplest analytical model gives optimistic predictions compared to real cases, with contrast up to 3 times better, which leads to DM surface height resolution requirements that are incorrectly relaxed by 70%. We show that taking into account the DM actuator shape, or influence function, improves the analytical predictions. However, we also find that end-to-end numerical simulations of the wavefront sensing and control process provide the most accurate predictions and recommend such an approach for setting robust requirements on the DM control electronics. From our experimental and numerical results, we conclude that a surface height resolution of ∼6 pm is required for imaging temperate terrestrial exoplanets around solar-type stars at wavelengths as small as 450 nm with coronagraph instruments on future space telescopes. Finally, we list the recognizable characteristics of quantization errors that may help determine if they are a limiting factor.

“…low-order aberrations, 47 they will have a relaxed h req (e.g., by a factor of >10× for vortex coronagraphs 5 ) and the wavefront correction may be updated at correspondingly faster rates.…”

Section: Photon-noise-limited Performancementioning

confidence: 99%

Wavefront sensing and control in space-based coronagraph instruments using Zernike’s phase-contrast method

Wallace

Steeves

et al. 2020

Self Cite

Future space telescopes with coronagraph instruments will use a wavefront sensor (WFS) to measure and correct for phase errors and stabilize the stellar intensity in high-contrast images. The HabEx and LUVOIR mission concepts baseline a Zernike wavefront sensor (ZWFS), which uses Zernike's phase contrast method to convert phase in the pupil into intensity at the WFS detector. In preparation for these potential future missions, we experimentally demonstrate a ZWFS in a coronagraph instrument on the Decadal Survey Testbed in the High Contrast Imaging Testbed facility at NASA's Jet Propulsion Laboratory. We validate that the ZWFS can measure low-and mid-spatial frequency aberrations up to the control limit of the deformable mirror (DM), with surface height sensitivity as small as 1 pm, using a configuration similar to the HabEx and LUVOIR concepts. Furthermore, we demonstrate closed-loop control, resolving an individual DM actuator, with residuals consistent with theoretical models. In addition, we predict the expected performance of a ZWFS on future space telescopes using natural starlight from a variety of spectral types. The most challenging scenarios require ∼1 h of integration time to achieve picometer sensitivity. This timescale may be drastically reduced by using internal or external laser sources for sensing purposes. The experimental results and theoretical predictions presented here advance the WFS technology in the context of the next generation of space telescopes with coronagraph instruments.