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NASA NTRS2018

Laboratory and On-Sky Validation of the Shaped Pupil Coronagraph's Sensitivity to Low-Order Aberrations with Active Wavefront Control

We present early laboratory simulations and extensive on-sky tests validating of the performance of a shaped pupil coronagraph (SPC) behind an extreme-AO (Adaptive Optics) corrected beam of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. In tests with the SCExAO internal source/wavefront error simulator, the normalized intensity profile for the SPC degrades more slowly than for the Lyot coronagraph as low-order aberrations reduce the Strehl ratio (S.R.) from extremely high values (S.R. approximately 0.93-0.99) to those characteristic of current ground-based extreme AO systems (S.R. approximately 0.74-0.93) and then slightly lower values down to S.R. approximately 0.57. On-sky SCExAO data taken with the SPC and other coronagraphs for brown dwarf/planet-hosting stars HD 1160 and HR 8799 provide further evidence for the SPC's robustness to low-order aberrations. From H-band Strehl ratios of 80 percent to 70 percent, the Lyot coronagraph's performance versus that of the SPC may degrade even faster on sky than is seen in our internal source simulations. The 5-sigma contrast also degrades faster (by a factor of two) for the Lyot than the SPC. The SPC we use was designed as a technology demonstrator only, with a contrast floor, throughput, and outer working angle poorly matched for SCExAO's current AO performance and poorly tuned for imaging the HR 8799 planets. Nevertheless, we detect HR 8799 cde with SCExAO/CHARIS using the SPC in broadband mode, where the signal-to-noise ratio for planet e is within 30 percent of that obtained using the vortex coronagraph. The shaped-pupil coronagraph is a promising design demonstrated to be robust in the presence of low-order aberrations and may be well-suited for future ground and space-based direct imaging observations, especially those focused on follow-up exoplanet characterization and technology demonstration of deep contrast within well-defined regions of the image plane.

Currie, Thayne↗

NASA NTRS2022

Initial Laboratory Demonstration of Multi-Star Wavefront Control at the Occulting Mask Coronagraph Testbed

Online Abstract: A majority of Sun-like stars, such as the A and B components of Alpha Centauri, have at least one stellar companion that can introduce additional noise into the field of view of any high-contrast imaging instrument. Multi-Star Wavefront Control (MSWC) is a wavefront-control technique that removes stellar leakage from both stellar components, enabling direct imaging of planets in many binary star systems. We present the latest experimental and modeling results obtained with MSWC as part of the technology development effort focusing on demonstrations conducted on the Occulting Mask Coronagraph (OMC) testbed at JPL. OMC has a layout similar to the Roman Space Telescope coronagraph instrument (CGI), and we used a MSWC mask similar to the one that was contributed to the Roman CGI. Our results represent the first demonstrations of this technique on the OMC testbed, with the ultimate goal of demonstrating full MSWC with validated models at contrast levels relevant to Roman CGI. Technical Review Abstract: A majority of Sun-like stars have at least one stellar companion that can introduce additional noise into the field of view of any high-contrast imaging instrument, limiting the achievable contrast. These include high-quality target stars such as the A and B components of Alpha Centauri, our nearest stellar neighbor. Enabling direct imaging of binary stars has the potential to increase the scientific yield for coronagraphic instruments planned on NASA's future space missions including the Roman Space Telescope and the next IR/O/UV Flagship recommended by Astro2020. Multi-Star Wavefront Control (MSWC) is a wavefront-control technique that simultaneously removes the (mutually incoherent) stellar leakage from both stellar components, enabling direct imaging of planets in many binary star systems. MSWC is an algorithmic technique and can be used with existing wavefront control systems on coronagraphic instruments (as well as starshades if a deformable mirror is available in the optical path). We summarize the latest experimental and numerical results obtained with MSWC as part of the technology development effort to demonstrate compatibility with existing high-contrast imaging platforms for this technique. The Super-Nyquist regime of MSWC was tested in vacuum at JPL's High Contrast Imaging Testbed (HCIT) on the Decadal Survey Testbed (DST) reaching 8.6e-9 contrast in a 10% band. Recently, the Occulting Mask Coronagraph (OMC) testbed at JPL is being prepared for demonstrations of Multi-Star Wavefront Control. A shaped pupil mask similar to the contributed MSWC mask on the Roman Space Telescope's coronagraph instrument has been recently manufactured including matching Lyot and focal plane masks and being installed on the OMC testbed. The goal of this experiment is a demonstration of MSWC using validated models on a testbed configuration and at contrast levels relevant to the Roman coronagraphic instrument.

High-contrast imaging↗

NASA NTRS2022

Modeling and Performance Analysis of the LUVOIR Coronagraph Instrument

Future space missions such as the Large UV/Optical/Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Observatory, when equipped with coronagraphs with active wavefront control to suppress starlight, will allow the discovery and characterization of habitable exoplanets. The Extreme Coronagraph for Living Planetary Systems (ECLIPS) is the coronagraph instrument on the LUVOIR Surveyor mission concept, an 8- to 15-m segmented telescope. ECLIPS is split into three channels, namely, UV (200 to 400 nm), optical (400 to 850 nm), and near IR (850 nm to 2 μm), with each channel equipped with two deformable mirrors for wavefront control, a suite of coronagraph masks, a low-order/out-of-band wavefront sensor, and separate science imagers and spectrographs. The apodized pupil Lyot coronagraph and the vector vortex coronagraph are the baselined mask technologies for ECLIPS to enable the required 10−10 contrast for observations in the habitable zones of nearby stars for LUVOIR-A (15-m telescope) and LUVOIR-B (8-m telescope), respectively. Their performance depends on active wavefront sensing and control, as well as metrology subsystems to compensate for aberrations induced by segment errors (e.g., piston and tip/tilt), secondary mirror misalignment, and global low-order wavefront errors. Here, we present the latest results of the simulation of these effects for the LUVOIR coronagraph instrument and discuss the achieved contrast for exoplanet detection and characterization after closed-loop wavefront estimation and control algorithms have been applied. Finally, we show simulated observations using high-fidelity spatial and spectral input models of complete planetary systems generated with the Haystacks code framework.

Roser Juanola-Parramon↗

NASA NTRS2022

JWST/MIRI Coronagraphic Performances as Measured on-Sky

Context . Characterization of directly imaged exoplanets is one of the most eagerly anticipated science functions of the James Webb Space Telescope . MIRI, the mid-IR instrument, has the capability to provide unique spatially resolved photometric data points in a spectral range never before achieved for such objects. Aims . We aim to present the very first on-sky contrast measurements of the MIRI coronagraphs. In addition to a classical Lyot coronagraph at the longest wavelength, this observing mode implements the concept of the four-quadrant phase mask for the very first time in a space telescope. Methods . We observed single stars together with a series of reference stars to measure raw contrasts as they are delivered on the detector, as well as reference-subtracted contrasts. Results . The MIRI coronagraphs achieve raw contrasts better than 10 −3 at the smallest angular separations (within 1″) and about 10 −5 farther out (beyond 5 ~ 6″). Subtracting the residual diffracted light left behind the coronagraph has the potential to bring the final contrast down to the background- and detector-limited noise floor at most angular separations (a few times 10 −5 at less than 1″). Conclusions . The MIRI coronagraphs behave as expected from simulations. In particular, the raw contrasts for all four coronagraphs are fully consistent with the diffractive model. Contrasts obtained by subtracting reference stars also meet expectations and are fully demonstrated for two four-quadrant phase masks (F1065C and F1140C). The worst contrast, measured at F1550C, is very likely due to a variation in the phase aberrations at the primary mirror during the observations, and not an issue with the coronagraph itself. We did not perform reference star subtraction with the Lyot mask at F2300C, but we anticipate that it would bring the contrast down to the noise floor.

High angular resolution instrumentation↗

NASA NTRSDate not supplied

Science Yield Estimates and Sensitivities With the AstroPIC Integrated Photonic Coronagraph for the Habitable Worlds Observatory

The Habitable Worlds Observatory (HWO) flagship has a goal to survey ~100 of the nearest stellar systems and their habitable zones in order to detector and spectroscopically characterize ~25 potentially “Earth-like planets” (or “Exoearths”). The HWO telescope will feature a >6-m diameter aperture and a coronagraph that will suppress starlight by ten orders of magnitude to enable the detection and characterization of Earth analogues in the habitable zone. Three Exploratory Analytic Cases (EACs) are currently considering different aperture configurations for HWO including on-axis and off-axis apertures and both different hexagonal and keystone segmentation configurations. Photonic Integrated Circuits (PICs) offer a path to miniaturize traditional, bulk optics coronagraph functionality reducing risk margins and increasing mission science exoearth yields for the HWO mission. We have developed a simulation pipeline that enables evaluation of the AstroPIC photonic integrated coronagraph through to estimates mission yields. We present sensitivities to aberrations for different types of segmentation and low-order aberrations for HWO EACs demonstrating that AstroPIC is suitable for both on-axis and off-axis configurations. We perform a parametric sweep of the exoearth science yield sensitivities in terms of key coronagraph parameters including coronagraphic end-to-end throughput, inner working angle, robustness to aberrations, and bandwidth. We consider both a hybrid and a pure photonic architecture; a pure integrated photonic architecture provides the greatest potential in science yield improvements, although a hybrid PIC limited in its numbers of modes can provide complementary science to a traditional, bulk-optic coronagraph and increasing the estimated science yield when operated jointly.

Photonics↗

NASA NTRS2004

Extra Solar Planetary Imaging Coronagraph and Science Requirements for the James Webb Telescope Observatory

1) Extra solar planetary imaging coronagraph. Direct detection and characterization of Jovian planets, and other gas giants, in orbit around nearby stars is a necessary precursor to Terrestrial Planet Finder 0 in order to estimate the probability of Terrestrial planets in our stellar neighborhood. Ground based indirect methods are biased towards large close in Jovian planets in solar systems unlikely io harbor Earthlike planets. Thus to estimate the relative abundances of terrestrial planets and to determine optimal observing strategies for TPF a pathfinder mission would be desired. The Extra-Solar Planetary Imaging Coronagraph (EPIC) is such a pathfinder mission. Upto 83 stellar systems are accessible with a 1.5 meter unobscured telescope and coronagraph combination located at the Earth-Sun L2 point. Incorporating radiometric and angular resolution considerations show that Jovians could be directly detected (5 sigma) in the 0.5 - 1.0 micron band outside of an inner working distance of 5/D with integration times of -10 - 100 hours per observation. The primary considerations for a planet imager are optical wavefront quality due to manufacturing, alignment, structural and thermal considerations. pointing stability and control, and manufacturability of coronagraphic masks and stops to increase the planetary-to- stellar contrast and mitigate against straylight. Previously proposed coronagraphic concepts are driven to extreme tolerances. however. we have developed and studied a mission, telescope and coronagraphic detection concept, which is achievable in the time frame of a Discovery class NASA mission. 2) Science requirements for the James Webb Space Telescope observatory. The James Webb Space Observatory (JWST) is an infrared observatory, which will be launched in 201 1 to an orbit at L2. JWST is a segmented, 18 mirror segment telescope with a diameter of 6.5 meters, and a clear aperture of 25 mA2. The telescope is designed to conduct imaging and spectroscopic observations from 0.6-27 microns. The primary mirror find and understand predicted first light objects, observe galaxies back to their earliest precursors so that we can understand their growth and evolution, unravel the birth and early evolution of stars and planetary systems, and study planetary systems and the origins of life. In this paper we discuss the science goals for JWST in the context of the performance requirements they levy on the observatory.

Clampin, Mark↗

NASA NTRS2011

Fine Guidance Sensing for Coronagraphic Observatories

Three options have been developed for Fine Guidance Sensing (FGS) for coronagraphic observatories using a Fine Guidance Camera within a coronagraphic instrument. Coronagraphic observatories require very fine precision pointing in order to image faint objects at very small distances from a target star. The Fine Guidance Camera measures the direction to the target star. The first option, referred to as Spot, was to collect all of the light reflected from a coronagraph occulter onto a focal plane, producing an Airy-type point spread function (PSF). This would allow almost all of the starlight from the central star to be used for centroiding. The second approach, referred to as Punctured Disk, collects the light that bypasses a central obscuration, producing a PSF with a punctured central disk. The final approach, referred to as Lyot, collects light after passing through the occulter at the Lyot stop. The study includes generation of representative images for each option by the science team, followed by an engineering evaluation of a centroiding or a photometric algorithm for each option. After the alignment of the coronagraph to the fine guidance system, a "nulling" point on the FGS focal point is determined by calibration. This alignment is implemented by a fine alignment mechanism that is part of the fine guidance camera selection mirror. If the star images meet the modeling assumptions, and the star "centroid" can be driven to that nulling point, the contrast for the coronagraph will be maximized.

Brugarolas, Paul↗

NASA NTRS2019

The LUVOIR Extreme Coronagraph for Living Planetary Systems (ECLIPS) II. Performance Evaluation, Aberration Sensitivity Analysis and Exoplanet Detection Simulations

Future space missions such as the Large UV-Optical-Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Observatory (HabEx) require coronagraphs with active wavefront control to suppress starlight to discover and characterize habitable exoplanets. The Extreme Coronagraph for Living Planetary Systems (ECLIPS) is the coronagraph instrument on the LUVOIR Surveyor mission concept, an 8–15m segmented telescope. ECLIPS is split into three channels: UV (200 to 400 nm), optical (400 nm to 850 nm), and NIR (850 nm to 2.0 microns), with each channel equipped with two deformable mirrors for wavefront control, a suite of coronagraph masks, a low-order/out-of-band wavefront sensor, and separate science imagers and spectrographs. The Apodized Pupil Lyot Coronagraph (APLC) and the Vector Vortex Coronagraph (VVC) are the baselined mask technologies for ECLIPS to enable the required 10 -10 contrast for observations in the habitable zones of nearby stars. Their performance depends on active wavefront sensing and control, as well as metrology subsystems to compensate for aberrations induced by segment errors (piston and tip/tilt, among others), secondary mirror misalignment, and global low-order wavefront errors. Here we present the latest results of the simulation of these effects for the two technologies and discuss the achieved contrast for exoplanet detection and characterization after closed-loop wavefront estimation and control algorithms have been applied. Finally, we show simulated observations using high-fidelity spatial and spectral input models of complete planetary systems generated with the Haystacks code framework.

Roser Juanola-Parramon↗

NASA NTRS2021

The Roman Space Telescope Coronagraph Technology Demonstration: Current Status and Relevance to Future Missions

The Nancy Grace Roman Space Telescope (formally WFIRST) will be launched in the mid-2020’s with an onboard coronagraph instrument which will serve as a technology demonstrator for exoplanet direct imaging. The Roman Coronagraph will be capable of detecting and characterizing exoplanets and circumstellar disks in visible light at an unprecedented contrast level of ~10-8 or lower. Such a contrast level, which is several magnitudes better than state-of-the-art visible or near-infrared coronagraphs, raises entirely new challenges that will be overcome using a combination of hardware, calibration and data processing. In particular, the Roman Coronagraph will be the first space-based coronagraphic instrument with real-time active wavefront control through the use of large format deformable mirrors, and its EMCCD detector will enable faint signal detection in photon-counting mode. The Roman Coronagraph passed its critical design review successfully in April 2021, and is now well on its path to demonstrate many core technologies at the levels required for future exo-Earth direct imaging missions.

Luchik, T.↗

NASA NTRS2004

The Sensitivity of Shaped Pupil Coronagraphs to Optical Aberrations

Unlike focal-plane coronagraphs that use occulting spots and Lyot stops to eliminate diffraction, pupil-plane coronagraphs operate by shaping the pupil to redirect the diffracted stellar light into a tight core. As in focal-plane coronagraphs, the optical aberrations in the telescope must be sufficiently corrected to enable high contrast imaging. However, in shaped-pupil coronagraphs, the low-order aberrations resulting from misalignment and optical figure drift have a much smaller influence upon the contrast at at the inner working angle. These weaker sensitivities greatly relax the strict low-order wavefront stability required for high-contrast imaging the cost of some throughput. In this paper, we present the simulated performance of the concentric ring shaped pupil concepts comparing them to focal-plane coronagraphs that are optimized for the same inner working angles.

extrasolar planets↗

NASA NTRS2011

Stability Error Budget for an Aggressive Coronagraph on a 3.8 m Telescope

We evaluate in detail the stability requirements for a band-limited coronagraph with an inner working angle as small as 2 lambda/D coupled to an off-axis, 3.8-m diameter telescope. We have updated our methodologies since presenting a stability error budget for the Terrestrial Planet Finder Coronagraph mission that worked at 4 lambda/D and employed an 8th-order mask to reduce aberration sensitives. In the previous work, we determined the tolerances relative to the total light leaking through the coronagraph. Now, we separate the light into a radial component, which is readily separable from a planet signal, and an azimuthal component, which is easily confused with a planet signal. In the current study, throughput considerations require a 4th-order coronagraph. This, combined with the more aggressive working angle, places extraordinarily tight requirements on wavefront stability and opto-mechanical stability. We find that the requirements are driven mainly by coma that leaks around the coronagraph mask and mimics the localized signal of a planet, and pointing errors that scatter light into the background, decreasing SNR. We also show how the requirements would be relaxed if a low-order aberration detection system could be employed.

error budget↗

NASA NTRS2015

Exoplanet Coronagraph Shaped Pupil Masks and Laboratory Scale Star Shade Masks: Design, Fabrication and Characterization

Star light suppression technologies to find and characterize faint exoplanets include internal coronagraph instruments as well as external star shade occulters. Currently, the NASA WFIRST-AFTA mission study includes an internal coronagraph instrument to find and characterize exoplanets. Various types of masks could be employed to suppress the host star light to about 10 -9 level contrast over a broad spectrum to enable the coronagraph mission objectives. Such masks for high contrast internal coronagraphic imaging require various fabrication technologies to meet a wide range of specifications, including precise shapes, micron scale island features, ultra-low reflectivity regions, uniformity, wave front quality, achromaticity, etc. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks by combining electron beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each, highlighting milestone accomplishments from the High Contrast Imaging Testbed (HCIT) at JPL and from the High Contrast Imaging Lab (HCIL) at Princeton University. We also present briefly the technologies applied to fabricate laboratory scale star shade masks.

black silicon↗

NASA NTRS2018

Apodized Pupil Lyot Coronagraphs Designs for Future Segmented Space Telescopes

A coronagraphic starlight suppression system situated on a future flagship space observatory offers a promising avenue to image Earth-like exoplanets and search for biomarkers in their atmospheric spectra. One NASA mission concept that could serve as the platform to realize this scientific breakthrough is the Large UV/Optical/IR Surveyor (LUVOIR). Such a mission would also address a broad range of topics in astrophysics with a multi-wavelength suite of instruments. The apodized pupil Lyot coronagraph (APLC) is one of several coronagraph design families that the community is assessing as part of NASAs Exoplanet Exploration Program Segmented aperture coronagraph design and analysis (SCDA) team. The APLC is a Lyot-style coronagraph that suppresses starlight through a series of amplitude operations on the on-axis eld. Given a suite of seven plausible segmented telescope apertures, we have developed an object-oriented software toolkit to automate the exploration of thousands of APLC design parameter combinations. This has enabled us to empirically establish relationships between planet throughput and telescope aperture geometry, inner working angle, bandwidth, and contrast level.In parallel with the parameter space exploration, we have investigated several strategies to improve the robust-ness of APLC designs to fabrication and alignment errors. We also investigate the combination of APLC withwavefront control or complex focal plane masks to improve inner working angle and throughput. Preliminaryscientic yield evaluations based on design reference mission simulations indicate the APLC is a very competitiveconcept for surveying the local exoEarth population with a mission like LUVOIR.

coronagraphic starlight suppression system↗

NASA NTRSDate not supplied

A New Integral Field Spectrograph for Broadband Coronagraph Demonstrations at the High Contrast Imaging Testbed Facility

An integral field spectrograph (IFS) camera may help fulfill the exoplanet characterization goals of a future Habitable Worlds Observatory. During the Nancy Grace Roman Space Telescope mission formulation phase, the Coronagraph Instrument Project established the laboratory performance baseline of a combined coronagraph and IFS system with the Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES; 1E-8 contrast over an 18% bandpass; 3--9 lambda/D bowtie-shaped control region). New laboratory demonstrations are needed to expand on this milestone in terms of contrast, bandpass, and field of view towards the requirements of a future mission capable of characterizing the atmospheres of Earth-like exoplanets. Here we present the design of a successor to PISCES that can observe a 20 lambda/D-diameter field of view with an instantaneous bandpass up to 30%, at a resolving power R > 70 at visible wavelengths. This instrument will interface with the existing coronagraph layout in the High Contrast Imaging Facility DST-2 vacuum chamber. The addition of a spectroscopic imaging camera at HCIT will benefit the wider coronagraph technology community by enabling other NASA-supported investigators to automatically obtain multi-wavelength measurements of speckles both inside and outside of their control region, and the instrument will support community-led demonstrations of high-order wavefront sensing and control techniques such as dark hole maintenance and linear dark field control.

coronagraph↗

NASA NTRSDate not supplied

Status and Predicted Performance for the AstroPIC Integrated Photonic Coronagraph

Integrated photonics is a promising coronagraph technology option for exoplanet-imaging missions like NASA’s Habitable Worlds Observatory flagship. It is theoretically capable of achieving better performance than traditional bulk-optic coronagraphs because arrays of integrated interferometers can be combined to implement any linear operator. However, photonic coronagraphs require significant maturation to be ready for a space telescope mission. The AstroPIC project is advancing this technology by developing a proof-of-concept integrated photonic coronagraph based on silicon photonic integrated circuit (PIC) technology. Specifically, the AstroPIC program is investigating the impact of a PIC coronagraph on the predicted scientific yield of the upcoming Habitable Worlds Observatory (HWO) mission concept. In this talk, we will present the current status of the AstroPIC design, including the layout of the most recent PIC. We will also present on the status of simulations that predict the performance of the instrument and feed into scientific yield estimations for HWO Exoploratory Analytic Cases (EACs) 1-3. Finally, we will present the status of the development of a PIC testbed at NASA Ames and results from preliminary PIC laboratory testing at Stanford.

Photonics↗

DOE OSTI2013

RING-APODIZED VORTEX CORONAGRAPHS FOR OBSCURED TELESCOPES. I. TRANSMISSIVE RING APODIZERS

The vortex coronagraph (VC) is a new generation small inner working angle (IWA) coronagraph currently offered on various 8 m class ground-based telescopes. On these observing platforms, the current level of performance is not limited by the intrinsic properties of actual vortex devices, but by wavefront control residuals and incoherent background (e.g., thermal emission of the sky), or the light diffracted by the imprint of the secondary mirror and support structures on the telescope pupil. In the particular case of unfriendly apertures (mainly large central obscuration) when very high contrast is needed (e.g., direct imaging of older exoplanets with extremely large telescopes or space-based coronagraphs), a simple VC, like most coronagraphs, cannot deliver its nominal performance because of the contamination due to the diffraction from the obscured part of the pupil. Here, we propose a novel yet simple concept that circumvents this problem. We combine a vortex phase mask in the image plane of a high-contrast instrument with a single pupil-based amplitude ring apodizer, tailor-made to exploit the unique convolution properties of the VC at the Lyot-stop plane. We show that such a ring-apodized vortex coronagraph (RAVC) restores the perfect attenuation property of the VC regardless of the size of the central obscuration, and for any (even) topological charge of the vortex. More importantly, the RAVC maintains the IWA and conserves a fairly high throughput, which are signature properties of the VC.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1995

Solar wind research with the Large Angle Spectroscopic Coronagraph (LASCO) experiment onboard the Solar and Heliospheric Observatory (SOHO) satellite

The ESA-NASA satellite, to be launched in October 1995, carries three nested coronagraphs, which will image the solar corona from 1.1 R(solar mass) to 30 R(solar mass). Super polished mirrors have been developed for the design of a mirror Lyot coronagraph which has a straylight level comparable with the coronal intensity from 1.1 R, to 30 R(solar mass) Coronal details can be imaged with a spatial resolution of 6 arc seconds. A Fabry Perot interferometer with a spectral resolution of 0.7 A at the wavelength of the green coronal emission line will allow the simultaneous construction of spectra over the entire field of view of 10(exp 6) pixels. The middle coronagraph (1.5 R(solar mass) - 6 R(solar mass)) and the outer coronagraph (3 R(solar mass) - 30 R(solar mass)) are externally occulted lens Lyot coronagraphs. Their straylight level 10(exp -11) B(solar mass) and 10(exp -12) B(solar mass) respectively is an order of magnitude smaller than the intensity of the corona. The sensitivity of LASCO to distinguish between different solar wind acceleration mechanisms will be discussed as well as its ability to discern different CME models.

Brueckner, G. E.↗

NASA NTRS2004

Study of High Performance Coronagraphic Techniques

The goal of the Study of High Performance Coronagraphic Techniques project (called CoronaTech) is: 1) to verify the Labeyrie multi-step speckle reduction method and 2) to develop new techniques to manufacture soft-edge occulter masks preferably with Gaussian absorption profile. In a coronagraph, the light from a bright host star which is centered on the optical axis in the image plane is blocked by an occulter centered on the optical axis while the light from a planet passes the occulter (the planet has a certain minimal distance from the optical axis). Unfortunately, stray light originating in the telescope and subsequent optical elements is not completely blocked causing a so-called speckle pattern in the image plane of the coronagraph limiting the sensitivity of the system. The sensitivity can be increased significantly by reducing the amount of speckle light. The Labeyrie multi-step speckle reduction method implements one (or more) phase correction steps to suppress the unwanted speckle light. In each step, the stray light is rephased and then blocked with an additional occulter which affects the planet light (or other companion) only slightly. Since the suppression is still not complete, a series of steps is required in order to achieve significant suppression. The second part of the project is the development of soft-edge occulters. Simulations have shown that soft-edge occulters show better performance in coronagraphs than hard-edge occulters. In order to utilize the performance gain of soft-edge occulters. fabrication methods have to be developed to manufacture these occulters according to the specification set forth by the sensitivity requirements of the coronagraph.

Crane, Phil↗