arXiv subjects

A J Eldorado Riggs

Publications and source records attributed to A J Eldorado Riggs.

27 records · Page 2Linked to original sources

arXiv2020

High-contrast Demonstration of an Apodized Vortex Coronagraph

High contrast imaging is the primary path to the direct detection and characterization of Earth-like planets around solar-type stars; a cleverly designed internal coronagraph suppresses the light from the star, revealing the elusive circumstellar companions. However, future large-aperture telescopes ($>$4~m in diameter) will likely have segmented primary mirrors, which causes additional diffraction of unwanted stellar light. Here we present the first high contrast laboratory demonstration of an apodized vortex coronagraph (AVC), in which an apodizer is placed upstream of a vortex focal plane mask to improve its performance with a segmented aperture. The gray-scale apodization is numerically optimized to yield a better sensitivity to faint companions assuming an aperture shape similar to the LUVOIR-B concept. Using wavefront sensing and control over a one-sided dark hole, we achieve a raw contrast of $2\times10^{-8}$ in monochromatic light at 775~nm, and a raw contrast of $4\times10^{-8}$ in a 10\% bandwidth. These results open the path to a new family of coronagraph designs, optimally suited for next-generation segmented space telescopes.

astro-ph.IM↗

arXiv2019

Scalar vortex coronagraph mask design and predicted performance

Vortex coronagraphs are an attractive solution for imaging exoplanets with future space telescopes due to their relatively high throughput, large spectral bandwidth, and low sensitivity to low-order aberrations compared to other coronagraphs with similar inner working angles. Most of the vortex coronagraph mask development for space applications has focused on generating a polychromatic, vectorial, optical vortex using multiple layers of liquid crystal polymers. While this approach has been the most successful thus far, current fabrication processes achieve retardance errors of 0.1-1.0$^\circ$, which causes a nonnegligible fraction of the starlight to leak through the coronagraph. Circular polarizers are typically used to reject the stellar leakage reducing the throughput by a factor of two. Vector vortex masks also complicate wavefront control because they imprint conjugated phase ramps on the orthogonal circular polarization components, which may need to be split in order to properly sense and suppress the starlight. Scalar vortex masks can potentially circumvent these limitations by applying the same phase shift to all incident light regardless of the polarization state and thus have the potential to significantly improve the performance of vortex coronagraphs. We present scalar vortex coronagraph designs that make use of focal plane masks with multiple layers of dielectrics that (a) produce phase patterns that are relatively friendly to standard manufacturing processes and (b) achieve sufficient broadband starlight suppression, in theory, for imaging Earth-like planets with future space telescopes.

astro-ph.IM↗

arXiv2018

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes II. Common path wavefront sensing/control and Coherent Differential Imaging

The Optimal Optical Coronagraph (OOC) Workshop held at the Lorentz Center in September 2017 in Leiden, the Netherlands, gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. In this second installment of a series of three papers summarizing the outcomes of the OOC workshop (see also~\citenum{ruane2018,snik2018}), we present an overview of common path wavefront sensing/control and Coherent Differential Imaging techniques, highlight the latest results, and expose their relative strengths and weaknesses. We layout critical milestones for the field with the aim of enhancing future ground/space based high contrast imaging platforms. Techniques like these will help to bridge the daunting contrast gap required to image a terrestrial planet in the zone where it can retain liquid water, in reflected light around a G type star from space.

astro-ph.IM↗

arXiv2018

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes III. Technology opportunities and pathways

The Optimal Optical CoronagraphWorkshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. This contribution is the final part of a series of three papers summarizing the outcomes of the workshop, and presents an overview of novel optical technologies and systems that are implemented or considered for high-contrast imaging instruments on both ground-based and space telescopes. The overall objective of high contrast instruments is to provide direct observations and characterizations of exoplanets at contrast levels as extreme as 10^-10. We list shortcomings of current technologies, and identify opportunities and development paths for new technologies that enable quantum leaps in performance. Specifically, we discuss the design and manufacturing of key components like advanced deformable mirrors and coronagraphic optics, and their amalgamation in "adaptive coronagraph" systems. Moreover, we discuss highly integrated system designs that combine contrast-enhancing techniques and characterization techniques (like high-resolution spectroscopy) while minimizing the overall complexity. Finally, we explore extreme implementations using all-photonics solutions for ground-based telescopes and dedicated huge apertures for space telescopes.

astro-ph.IM↗

arXiv2017

Prospects for exoplanet imaging in multi-star systems with starshades

We explore the capabilities of a starshade mission to directly image multi-star systems. In addition to the diffracted and scattered light for the on-axis star, a multi-star system features additional starlight leakage from the off-axis star that must also be controlled. A basic option is for additional starshades to block the off-axis stars. An interesting option takes the form of hybrid operation of a starshade in conjunction with an internal starlight suppression. Two hybrid scenarios are considered. One such scenario includes the coronagraph instrument blocking the on-axis star, with the starshade blocking off-axis starlight. Another scenario uses the wavefront control system in the coronagraph instrument and using a recent Super-Nyquist Wavefront Control (SNWC) technique can remove the off-axis stellar leakage to enable a region of high-contrast around the on-axis star blocked by the starshade.We present simulation results relevant for the WFIRST telescope.

astro-ph.IM↗

arXiv2016

Recursive Starlight and Bias Estimation for High-Contrast Imaging with an Extended Kalman Filter

For imaging faint exoplanets and disks, a coronagraph-equipped observatory needs focal plane wavefront correction to recover high contrast. The most efficient correction methods iteratively estimate the stellar electric field and suppress it with active optics. The estimation requires several images from the science camera per iteration. To maximize the science yield, it is desirable both to have fast wavefront correction and to utilize all the correction images for science target detection. Exoplanets and disks are incoherent with their stars, so a nonlinear estimator is required to estimate both the incoherent intensity and the stellar electric field. Such techniques assume a high level of stability found only on space-based observatories and possibly ground-based telescopes with extreme adaptive optics. In this paper, we implement a nonlinear estimator, the iterated extended Kalman filter (IEKF), to enable fast wavefront correction and a recursive, nearly-optimal estimate of the incoherent light. In Princeton's High Contrast Imaging Laboratory we demonstrate that the IEKF allows wavefront correction at least as fast as with a Kalman filter and provides the most accurate detection of a faint companion. The nonlinear IEKF formalism allows us to pursue other strategies such as parameter estimation to improve wavefront correction.

astro-ph.IM↗

arXiv2016

Shaped Pupil Lyot Coronagraphs: High-Contrast Solutions for Restricted Focal Planes

Coronagraphs of the apodized pupil and shaped pupil varieties use the Fraunhofer diffraction properties of amplitude masks to create regions of high contrast in the vicinity of a target star. Here we present a hybrid coronagraph architecture in which a binary, hard-edged shaped pupil mask replaces the gray, smooth apodizer of the apodized pupil Lyot coronagraph (APLC). For any contrast and bandwidth goal in this configuration, as long as the prescribed region of contrast is restricted to a finite area in the image, a shaped pupil is the apodizer with the highest transmission. We relate the starlight cancellation mechanism to that of the conventional APLC. We introduce a new class of solutions in which the amplitude profile of the Lyot stop, instead of being fixed as a padded replica of the telescope aperture, is jointly optimized with the apodizer. Finally, we describe shaped pupil Lyot coronagraph (SPLC) designs for the baseline architecture of the Wide-Field Infrared Survey Telescope-Astrophysics Focused Telescope Assets (WFIRST-AFTA) coronagraph. These SPLCs help to enable two scientific objectives of the WFIRST-AFTA mission: (1) broadband spectroscopy to characterize exoplanet atmospheres in reflected starlight and (2) debris disk imaging.

astro-ph.IM↗

arXiv2015

Coronagraph-Integrated Wavefront Sensing with a Sparse Aperture Mask

Stellar coronagraph performance is highly sensitive to optical aberrations. In order to effectively suppress starlight for exoplanet imaging applications, low-order wavefront aberrations entering a coronagraph such as tip-tilt, defocus and coma must be determined and compensated. Previous authors have established the utility of pupil-plane masks (both non-redundant/sparse-aperture and generally asymmetric aperture masks) for wavefront sensing. Here we show how a sparse aperture mask (SAM) can be integrated with a coronagraph to measure low-order, differential phase aberrations. Starlight rejected by the coronagraph's focal plane stop is collimated to a relay pupil, where the mask forms an interference fringe pattern on a subsequent detector. Our numerical Fourier propagation models show that the information encoded in the fringe intensity distortions is sufficient to accurately discriminate and estimate Zernike phase modes extending from tip-tilt up to radial degree $n=5$, with amplitude up to $λ/20$ RMS. The SAM sensor can be integrated with both Lyot and shaped pupil coronagraphs (SPC) at no detriment to the science beam quality. We characterize the reconstruction accuracy and the performance under low flux/short exposure time conditions, and place it in context of other coronagraph wavefront sensing schemes.

astro-ph.IM↗

arXiv2012

Broadband Focal Plane Wavefront Control of Amplitude and Phase Aberrations

The Stroke Minimization algorithm developed at the Princeton High Contrast Imaging Laboratory has proven symmetric dark hole generation using minimal stroke on two deformable mirrors (DM) in series. The windowed approach to Stroke Minimization has proven symmetric dark holes over small bandwidths by using three wavelengths to define the bandwidth of correction in the optimization problem. We address the relationship of amplitude and phase aberrations with wavelength, how this changes with multiple DMs, and the implications for simultaneously correcting both to achieve symmetric dark holes. Operating Stroke Minimization in the windowed configuration requires multiple wavelength estimates. To save on exposures, a single estimate is extrapolated to bounding wavelengths using the established relationship in wavelength to produce multiple estimates of the image plane electric field. Here we demonstrate better performance by improving this extrapolation of the estimate to other wavelengths. The accuracy of the functional relationship will ultimately bound the achievable bandwidth, therefore as a metric these results are also compared to estimating each wavelength separately. In addition to these algorithm improvements, we also discuss a laboratory upgrade and how it can better simulate broadband starlight. We also discuss the possibility of leveraging two DMs in series to directly estimate the electric field over a narrow bandwidth and the challenges associated with it.

astro-ph.IM↗