This PDF file contains the front matter associated with SPIE Proceedings Volume 8151, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Coronagraph technology is advancing and promises to enable direct imaging and spectral characterization of extrasolar Earth-like planets in the 2020 decade with a telescope as small as 1.5m. A small Explorer-sized telescope can also be launched in the 2010 decade capable of seeing debris disks as dim as tens of zodis and potentially a few large planets. The Phase Induced Amplitude Apodization (PIAA) coronagraph makes such aggressive performance possible, providing high throughput and high contrast close to the diffraction limit. We report on the latest results from a testbed at NASA Ames that is focused on developing and testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in an actively thermally stabilized air environment, and to complement collaborative efforts at NASA JPL's High Contrast Imaging Testbed. For our wavefront control we are using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promise to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. We describe our lab progress and results, which include (as of August 2011): the demonstration of 1.9x10^-8 average raw contrast in a dark zone from 2.0 - 3.4 λ/D and of 1.2x10^-6 contrast from 1.5-2.0 λ/D (in monochromatic light); the testing of the next-generation reflective PIAA mirror set built by Tinsley and designed for broadband; and finally, discuss our most important past limiting factors as well as expected future ones.

Since the radius of curvature of a mirror cannot be zero, the apodization that is created by a phase-induced amplitude apodizer (PIAA) formed by a pair of mirrors cannot be zero at the edge of the pupil. If contrasts lower than 10^-10 must be obtained, then an additional apodizer must be used with the PIAA mirrors. This has a consequence on the throughput of the system, as well as on its inner working angle (IWA). The intensity distribution in the final pupil plane computed in the ray-optics approximation is misleading, and diffraction must be taken into account to evaluate the true performance of the system. We compute the propagated electric field using two different tools: the semi-analytical model developed by Pueyo and a purely numerical model based on the Huygens integral. It is shown that for higher Fresnel numbers, the agreement between the beams computed using both propagators is stronger, and that for too low Fresnel numbers, the contrast computed using the semi-analytical model can be 2 orders of magnitude higher than the one computed by a numerical evaluation of the Huygens integral. We then study the impact of surface aberrations introduced on the mirrors of the PIAA. The surface quality of the mirrors limits the performance of the system, and the IWA increases linearly with the root-mean-square (RMS) of the aberrations. For a typical set of mirrors, errors of 10nm RMS can increase the IWA by 0.5 to 1λ/D for a contrast of 10^-10, and, in the case of a contrast of 10^-8, the IWA is maintained to 2 λ/D as long as the errors are smaller than 20nm RMS.

We present high-contrast images from laboratory testing of a Phase Induced Amplitude Apodization (PIAA) coronagraph at NASA's High Contrast Imaging Testbed (HCIT). Using a deformable mirror and wavefront estimation and control algorithms, we create a "dark hole" in the monochromatic point-spread function with an inner working angle of 2.05 fλ/D, with a mean intensity 3.5×10^-8. We discuss the contributions to this floor, and the techniques being developed to improve it. We also present simulations that investigate the effect of Lyot stops of various sizes, and conclude that a Lyot stop is necessary for 10^-9 performance but that an annular postapodizer is not necessary.

Off-axis, high-sag PIAA optics for high contrast imaging present challenges in manufacturing and testing. With smaller form factors and consequently smaller surface deformations (< 80 microns), diamond turned fabrication of these mirrors becomes feasible. Though such a design reduces the system throughput, it still provides 2λ/D inner working angle. We report on the design, fabrication, measurements, and initial assessment of the novel PIAA optics in a coronagraph testbed. We also describe, for the first time, a four mirror PIAA coronagraph that relaxes apodizer requirements and significantly improves throughput while preserving the low-cost benefits.

The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory employs a broadband wavefront correction algorithm called Electric Field Conjugation (EFC) to obtain the required 10^-10 contrast. This algorithm works with one deformable mirror (DM) to estimate the electric-field to be controlled, and with one or multiple DM's to create a "darkhole" in a predefined region of the image plane where terrestrial planets would be found. We have investigated the effects of DM actuator errors and the optic position errors on the efficiency of the EFC algorithm in a Lyot coronagraph configuration. The structural design of the optical system as well as the parameters of various optical elements used in the analysis are drawn from those of the HCIT system that have been implemented with one DM. The simulation takes into account the surface errors of various optical elements. Results of some of these studies have been verified by actual measurements.

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris- Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive optics, extremely large ground-based telescopes, and space-based internal coronagraphs.

We evaluate in detail the stability requirements for a band-limited coronagraph with an inner working angle as small as 2 λ/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 λ/D and employed an 8th-order mask to reduce aberration sensitivities. 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.

In this paper are discussed the nulling and imaging properties of monolithic pupil telescopes equipped with a focal plane waveguide array, which could be envisaged as precursor space missions for future nulling interferometers or coronagraphs searching for habitable planets outside of our solar system. Three different concepts of nulling telescopes are reviewed, namely the Super-Resolving Telescope (SRT) having multiple, non-overlapping exit sub-apertures and the Sheared-Pupil Telescope (SPT), either unmasked or masked with a Lyot stop placed at its exit pupil plane. For each case simple theoretical relationships allowing to estimate the nulling rate, Signal-to-Noise Ratio (SNR) and Inner Working Angle (IWA) of the telescope are established or recalled, and numerical simulations are conducted. The preliminary results of this study show that the most promising designs should either be a SRT of high radiometric efficiency associated with an adequate leakage calibration procedure, or a masked SPT with potentially deeper nulling rates but lower SNR, depending on what kind of performance is to be preferred.

Stabilizing a nulling interferometer at a nanometric level is the key issue to obtain deep null depths. The PERSEE breadboard has been designed to study and optimize the operation of cophased nulling bench in the most realistic disturbing environment of a space mission. This presentation focuses on the current results of the PERSEE bench. In terms of metrology, we cophased at 0.33 nm rms for the piston and 60 mas rms for the tip/tilt. A Linear Quadratic Gaussian (LQG) control coupled with an unsupervised vibration identification allows us to maintain that level of correction, even with characteristic vibrations of nulling interferometry space missions. These performances, with an accurate design and alignment of the bench, currently lead to a polychromatic unpolarised null depth of 8.9 × 10^-6 stabilized at 2.7 × 10^-7 on the [1.65 - 2.45] μm spectral band (37% bandwidth). With those significant results, we give the first more general lessons we have already learned from this experiment, both at system and component levels for a future space mission.

Polarization holographic element with complex distribution of anisotropy and gyrotropy is suggested for astropolarimetry by means of real time analysis of the state and degree of polarization (also the dispersion of this state) of light that went into the entrance pupil of the telescope. The element decomposes the light incident on it into the orthogonal circular and linear bases. Simultaneous measurement of the intensities of diffracted beams allows all four Stokes parameters to be determined and the dispersion of this state. The possibility of the creation of suitable higheffective and extremely compact element and its application for detection and characterization of exsoplanets is discussed.

The last decade has seen great advances in interferometric nulling technology, propelled at first by the SIM and KECK nulling programs and then by the Terrestrial Planet Finder Interferometer (TPF-I). In the infrared at N-band (using a CO2 laser at 10.6 micron wavelength) the first million to one nulls were reported on a KECK testbed in 2003. For TPF-I, nulls needed to be both deep and broadband, and a suite of testbeds was designed and built to study all aspects of achromatic nulling and system implementation, including formation flying technology. Also, observatory designs were drawn up and studied against performance models. Modeling revealed that natural variations in the alignment and control of the optical system produced an "instability noise" signal and this realization eventually led to a redesign of the layout to a rectangular formation. The complexity of the early TPF-I spacecraft design was mitigated by the infusion of ideas from Europe and produced the current X-Array design which utilizes simple reflectors to form the apertures together with a stretched three dimensional formation geometry. This paper summarizes the main achievements of the infrared nulling technology program including the development of adaptive nulling for broadband performance and the demonstration of starlight suppression by 100 million to one.

As part of the NASA ROSES Technology Development for Exoplanet Missions (TDEM) program, we are conducting a study of three internal coronagraphs (PIAA, vector vortex, hybrid bandlimited) to understand their behaviors in realistically-aberrated systems with wavefront control (deformable mirrors). This study consists of two milestones: (1) develop wavefront propagation codes appropriate for each coronagraph that are accurate to 1% or better (compared to a reference algorithm) but are also time and memory efficient, and (2) use these codes to determine the wavefront control limits of each architecture. We discuss the results from the study so far, with emphasis on representing the PIAA coronagraph and its wavefront control behavior.

Herein we report on the development, sensing and control and our first results with the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraph (VNC) for exoplanet coronagraphy. 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 (GSFC) has a well-established effort to develop VNC technologies, and has developed an incremental sequence of VNC testbeds to advance this approach and the enabling technologies associated with it. We discuss the continued 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 10⁸, 10⁹, and ideally 10¹⁰ at an inner working angle of 2*λ/D. 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 initial laboratory results, the optical configuration, critical technologies and the null sensing and control approach.

We report our best laboratory contrast demonstrations achieved to date. We review the design, fabrication, performance, and future prospects of a hybrid focal plane occulter for exoplanet coronagraphy. Composed of thickness-profiled metallic and dielectric thin films vacuum deposited on a fused silica substrate, the hybrid occulter uses two superimposed thin films for control over both the real and imaginary parts of the complex attenuation pattern. Together with a deformable mirror for adjustment of wavefront phase, the hybrid Lyot coronagraph potentially exceeds billion-toone contrast over dark fields extending to within angular separations of 3 λ/D from the central star, over spectral bandwidths of 20% or more, and with throughput efficiencies up to 60%. We report laboratory contrasts of 3×10^-10 over 2% bandwidths, 6×10^-10 over 10% bandwidths, and 2×10^-9 over 20% bandwidths, achieved across high contrast fields extending from an inner working angle of 3 λ/D to a radius of 15 λ/D. Occulter performance is analyzed in light of recent experiments and optical models, and prospects for further improvements are summarized. The science capabilities of the hybrid Lyot coronagraph are compared with requirements of the ACCESS mission, a representative exoplanet space telescope concept study for the direct imaging and spectroscopy of exoplanet systems. This work has been supported by NASA's Technology Demonstration for Exoplanet Missions (TDEM) program.

The Phase Induced Amplitude Apodization (PIAA) concept uses aspheric optics to apodize a telescope beam for high contrast imaging. The lossless apodization, achieved through geometrical redistribution of the light (beam shaping) allows designs of high performance coronagraphs, ideally suited for direct imaging of exoplanets similar to Earth around nearby stars. The PIAA coronagraph concept has evolved since its original formulation to mitigate manufacturing challenges and improve performance. Our group is currently aiming at demonstrating PIAA coronagraphy in the laboratory to 1e-9 raw contrast at 2 λ/D separation. Recent results from the High Contrast Imaging Testbed (HCIT) at NASA JPL and the PIAA testbed at NASA Ames demonstrate contrasts about one order of magnitude from this goal at 2 λ/D. In parallel with our high contrast demonstration at 2λ/D, we are developing and testing new designs at a complementary testbed at NASA Ames, and solving associated technical challenges. Some of these new PIAA designs have been tested that can further mitigate PIAA manufacturing challenges while providing theoretically total starlight extinction and offering 50% throughput at less than 1 λ/D. Recent tests demonstrated on the order of 1e-6 contrast close to 1 λ/D (while maintaining 5e-8 contrast at 2 λ/D).

A 4-8m diameter telescope carrying a coronagraph instrument is a leading candidate for an anticipated flagship mission to detect and characterize Earth-size exoplanets in the 2020s.1 Many candidate coronagraph instruments have been proposed, and one is close to meeting some of the principal requirements for that mission. But the telescope and instrument will need exquisite stability and precise control of the incoming wavefront to enable detection of faint companions (10^-10of the star) at an angular separation of 2-4 Airy radii. In particular, wavefront errors cause speckles in the image, and variations in those speckles can confound the exoplanet detection. This challenge is compounded by the background light from zodiacal dust around our Sun and the target star, which limits the speed with which we can estimate and correct the speckles. We are working on developing coherent speckle detection techniques that will allow rapid calibration of speckles on the science detector, allowing subtraction in post-processing or correction with deformable mirrors. The expected speed improvement allows a much quicker timeline for measurement & calibration, which reduces the required telescope stability requirement and eases both the flight system design and the challenge of ground testing. We will describe the experiments and summarize progress to date.

External occulters provide the starlight suppression needed for detecting and characterizing exoplanets with a much simpler telescope and instrument than is required for the equivalent performing coronagraph. In this paper we describe progress on our Technology Development for Exoplanet Missions project to design, manufacture, and measure a prototype occulter petal. We focus on the key requirement of manufacturing a precision petal while controlling its shape within precise tolerances. The required tolerances are established by modeling the effect that various mechanical and thermal errors have on scatter in the telescope image plane and by suballocating the allowable contrast degradation between these error sources. We discuss the deployable starshade design, representative error budget, thermal analysis, and prototype manufacturing. We also present our metrology system and methodology for verifying that the petal shape meets the contrast requirement. Finally, we summarize the progress to date building the prototype petal.

This paper summarizes progress of a project to develop and advance the maturity of photon-counting detectors for NASA exoplanet missions. The project, funded by NASA ROSES TDEM program, uses a 256×256 pixel silicon Geigermode avalanche photodiode (GM-APD) array, bump-bonded to a silicon readout circuit. Each pixel independently registers the arrival of a photon and can be reset and ready for another photon within 100 ns. The pixel has built-in circuitry for counting photo-generated events. The readout circuit is multiplexed to read out the photon arrival events. The signal chain is inherently digital, allowing for noiseless transmission over long distances. The detector always operates in photon counting mode and is thus not susceptible to excess noise factor that afflicts other technologies. The architecture should be able to operate with shot-noise-limited performance up to extremely high flux levels, >10⁶ photons/second/pixel, and deliver maximum signal-to-noise ratios on the order of thousands for higher fluxes. Its performance is expected to be maintained at a high level throughout mission lifetime in the presence of the expected radiation dose.

The New Worlds, New Horizons report released by the Astronomy and Astrophysics Decadal Survey Board in 2010 listed the Wide Field Infrared Survey Telescope (WFIRST) as the highest-priority large space mission for the coming decade. This observatory will provide wide-field imaging and slitless spectroscopy at near infrared wavelengths. The scientific goals are to obtain a statistical census of exoplanets using gravitational microlensing, measure the expansion history of and the growth of structure in the Universe by multiple methods, and perform other astronomical surveys to be selected through a guest observer program. A Science Definition Team has been established to assist NASA in the development of a Design Reference Mission that accomplishes this diverse array of science programs with a single observatory. In this paper we present the current WFIRST payload concept and the expected capabilities for planet detection. The observatory, with science goals that are complimentary to the Kepler exoplanet transit mission, is designed to complete the statistical census of planetary systems in the Galaxy, from habitable Earth-mass planets to free floating planets, including analogs to all of the planets in our Solar System except Mercury. The exoplanet microlensing survey will observe for 500 days spanning 5 years. This long temporal baseline will enable the determination of the masses for most detected exoplanets down to 0.1 Earth masses.

SPHERE, the extra-solar planet imager for the Very Large Telescope is a program that has been running since 2006. The instrument is now nearing completion and it is in the final integration stage. The 3 science instruments of SPHERE are now complete and have passed the internal acceptance review while the complex common path with the extreme Adaptive optics system, the coronographs and the calibration module is aggressively progressing. This paper reviews the performance of the Common Path (CP) and three science instruments of SPHERE: IRDIS, the dual band imager; IFS, the integral field spectrograph and ZIMPOL, the imaging polarimeter. We also present an outlook at the final system integration.

SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. The instrument will search for direct light from old planets with orbital periods of several months to several years as we know them from our solar system. These are planets which are in or close to the habitable zone. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from extrasolar planets. The search for reflected light from extra-solar planets is very demanding because the signal decreases rapidly with the orbital separation. For a Jupiter-sized object and a separation of 1 AU the planet/star contrast to be achieved is on the order of 10^-8 for a successful detection. This is much more demanding than the direct imaging of young self-luminous planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of 2012. ZIMPOL is currently in the subsystem testing phase. We describe the results of verification and performance testing done at the NOVA-ASTRON lab. We will give an overview of the system noise performance, the polarimetric accuracy and the high contrast testing. For the high contrast testing we will describe the impact of crucial system parameters on the contrast performance. SPHERE is an instrument designed and built by a consortium consisting of IPAG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève, ETH, NOVA, ONERA and ASTRON in collaboration with ESO.

In 2009 our group started the integration of the SCExAO project, a highly flexible, open platform for high contrast imaging at the highest angular resolution, inserted between the coronagraphic imaging camera HiCIAO and the 188-actuator AO system of Subaru. In its first version, SCExAO combines a MEMS-based wavefront control system feeding a high performance PIAA-based coronagraph. It also includes a coronagraphic low-order wavefront sensor, a non-redundant aperture mask and a visible imaging mode, all of them designed to take full advantage of the angular resolution that an 8-meter telescope has to offer. SCExAO is currently undergoing commissioning, and this paper presents the first on-sky results acquired in August 2011, using together Subaru's AO system, SCExAO and HiCIAO.

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is an instrument designed to be inserted between the Subaru AO188 system and the infrared HiCIAO camera in order to greatly improve the contrast in the very close (less than 0.5") neighbourhood of stars.Next to the infrared coronagraphic path, a visible scientific path, based on a EMCCD camera, has been implemented. Benefiting from both AO correction and new data processing techniques, it is a powerful tool for high angular resolution imaging and opens numerous new science opportunities. A factor 2 to 3 in Strehl ratio is obtained compared to the AO long exposure time: up to 25% Strehl in the 650nm wavelength, depending on the image processing algorithm used and the seeing conditions. The system is able to deliver diffraction limited images at 650 nm (17 mas FWHM). Our baseline image processing algorithm is based on the selection of the best signal for each spatial frequency. We demonstrate that this approach offers significantly better results than the classical select, shift and add approach (lucky imaging).

A concept for high precision astrometry with a conventional wide field telescope is presented, enabling a space telescope to perform simultaneously coronagraphic imaging of exoplanets, astrometric measurement of their orbits and masses, and deep wide field imaging for a wide range of astrophysical investigations. Our concept uses a diffractive telescope pupil (primary mirror), obtained by placing a regular grid of small sub millimeter spots on the primary mirror coating. When the telescope is pointed at a bright star, the wide field image contains both a large number of background stars used for astrometric referencing, and faint diffraction spikes created by the grid of dots on the primary mirror. The diffraction spikes encode instrumental astrometric distortions due to optics or the detector, allowing precise measurement of the central star against a large number of faint background stars. With up to a few percent of the primary mirror area covered by the dots, the fraction of the central starlight located in the diffraction spikes is kept sufficiently small to allow full sensitivity deep imaging over the telescope's field of view. Since the dots are regularly spaced, they do not diffract light at small angular separations, and therefore allow full coronagraphic imaging capability. We show that combining simultaneous astrometric and coronagraphic measurements allows improved detection and characterization of exoplanets by constraining the planet(s) characteristics with both measurements. Our preliminary astrometric accuracy error budget shows that sub-micro arcsecond astrometry can be achieved with a 1.4 m diameter telescope, and that astrometric accuracy improves rapidly with telescope diameter.

The practical use of astrometry to detect exoplanets via the reflex motion of the parent star depends critically on the elimination of systematic noise floors in imaging systems. In the diffractive pupil technique proposed for space-based detection of exo-earths, extended diffraction spikes generated by a dotted primary mirror are referenced against a widefield grid of background stars to calibrate changing optical distortion and achieve microarcsecond astrometric precision on bright targets (Guyon et al. 2010). We describe applications of this concept to ground-based uncrowded astrometry using a diffractive, monopupil telescope and a wide-field camera to image as many as ~4000 background reference stars. Final relative astrometric precision is limited by differential tip/tilt jitter caused by high altitude layers of turbulence. A diffractive 3-meter telescope is capable of reaching ~35 μas relative astrometric error per coordinate perpendicular to the zenith vector in three hours on a bright target star (I < 10) in fields of moderate stellar density (~40 stars arcmin^-2 with I < 23). Smaller diffractive apertures (D < 1 m) can achieve 100-200 μas performance with the same stellar density and exposure time and a large telescope (6.5-10 m) could achieve as low as 10 μas, nearly an order of magnitude better than current space-based facilities. The diffractive pupil enables the use of larger fields of view through calibration of changing optical distortion as well as brighter target stars (V < 6) by preventing star saturation. Permitting the sky to naturally roll to average signals over many thousands of pixels can mitigate the effects of detector imperfections.

Detection of earth-size exoplanets using the astrometric signal of the host star requires sub microarcsecond measurement precision. One major challenge in achieving this precision using a medium-size (<2-m) space telescope is the calibration of dynamic distortions. The researchers propose a diffractive pupil technique that uses an array of approximately 50um dots on the primary mirror that generate polychromatic diffraction spikes in the focal plane. The diffraction spikes encode optical distortions in the optical system and may be used to calibrate astrometric measurements. This concept can be used simultaneously with coronagraphy for exhaustive characterization of exoplanets (mass, spectra, orbit). At the University of Arizona, a high precision astrometry laboratory is being developed to demonstrate the capabilities of this diffractive pupil concept. The researchers aim to achieve 10 μas single-axis precision in the laboratory, simulating 0.14 μas precision on a 1.4 m space telescope. This paper describes this laboratory and presents the data and results obtained so far.

NEAT, Nearby Exo-Earth Astrometric Telescope is a medium-small telescope ~ 1m in diameter that is designed to make ultra precise < 1 uas (microarcsec) astrometric measurements of nearby stars in a ~ 1hr observation. Four major error sources prevent normal space telescopes from obtaining accuracies close to 1 uas. Even with a small 1m telescope, photon noise is usually not a problem for the bright nearby target stars. But in general, the reference stars are much fainter. Typically a field of view of ~0.5 deg dia is needed to obtain enough bright reference stars. The NEAT concept uses a very simple but unusual design to avoid optically induced astrometric errors. The third source of error is the accuracy and stability of the focal plane. A 1uas error over a ~2000 arcsec field of view implies the focal plane is accurate or at least stable to 5 parts in 10¹⁰ over the lifetime of the mission (~5yrs). The 4th class of error has to do with our knowledge of the PSF and how that PSF is sampled by an imperfect detector. A Nyquist sampled focal plane would have > 2 pixels per λ/D, and centroiding to 1uas means centroiding to 10^-5 pixels. This paper describes the mission concept, and an overview of the technology needed to perform 1uas astrometry with a small telescope, and how we overcome problems 1 and 2. A companion paper will describe the technical progress we've made in solving problems 3 and 4.

The search for Earth-mass planets in the habitable zones of nearby Sun-like stars is an important goal of astrophysics. This search is not feasible with the current slate of astronomical instruments. We propose a new concept for microarcsecond astrometry which uses a simplified instrument and hence promises to be low cost. The concept employs a telescope with only a primary, laser metrology applied to the focal plane array, and new algorithms for measuring image position and displacement on the focal plane. The required level of accuracy in both the metrology and image position sensing is at a few micro-pixels. We have begun a detailed investigation of the feasibility of our approach using simulations and a micro-pixel image position sensing testbed called MCT. So far we have been able to demonstrate that the pixel-to-pixel distances in a focal plane can be measured with a precision of 20 micro-pixels and image-to-image distances with a precision of 30 micro-pixels. We have also shown using simulations that our image position algorithm can achieve accuracy of 4 micro-pixels in the presence of λ/20 wavefront errors.

Space-based coronagraphs for future earth-like planet detection will require focal plane wavefront control techniques to achieve the necessary contrast levels. These correction algorithms are iterative and the control methods require an estimate of the electric field at the science camera, which requires nearly all of the images taken for the correction. In order to maximize science time the amount of time required for correction must be minimized, which means reducing the number of exposures required for correction. This means reducing both the number of iterations and the number of exposures per iteration required to achieve a targeted contrast. Given the large number of images required for estimation, the ideal choice is to use fewer exposures to estimate the electric field. Here we demonstrate an optimal estimator that uses prior knowledge to create the estimate of the electric field. In this way we can optimally estimate the electric field by minimizing the number of exposures required to estimate under an error constraint. The performance of this method is compared to a pairwise estimator which is designed to give the least-squares minimal error. This allows us to evaluate the number of images necessary to achieve a contrast target and is the first step towards generating an adaptive algorithm which combines estimation and control to optimize the entire correction problem.

Numerous coronagraph designs for high-contrast imaging in space have been proposed, differentiated by various performance metrics, such as throughput, inner working angle, bandwidth, ease of implementation (a surrogate for cost), sensitivity, and robustness. In all cases, the performance of the coronagraph is limited by wavefront aberrations in the system, necessitating a deformable mirror (DM) wavefront control system. Traditionally, coronagraphs are designed to achieve the targeted contrast assuming perfect optics, then combined with the controller to correct aberrations in a small dark hole reachable by the DMs. This paper shows how all coronagraphs adjust amplitude and are thus limited by amplitude errors. We propose a unified design approach where the coronagraph is only designed to achieve contrast to the level determined by the amplitude error and in a dark hole consistent with the wavefront controller. The deformable mirrors are then used with the already existing algorithms to generate the remainder of the dark hole. We show new shaped pupil designs with much increased throughput and smaller inner working angles consistent with this approach. These new designs can also be used with on-axis and segmented telescopes.

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. We extend the concept of minimizing DM actuation to achieve symmetric dark holes in broadband light. This requires simultaneously correcting both amplitude and phase aberrations over the bandwidth. Here we address the relationship of amplitude and phase aberrations with wavelength and the implication for wavefront control and design tolerances. This drives the number of deformable mirrors, their locations in the optical path, and design constraints on the deformable mirrors. Broadband suppression is achieved experimentally by using three wavelengths to define the bandwidth of correction in the optimization problem. This windowed approach to Stroke Minimization makes the optimization in wavelength tractable and allows for estimation only at a single wavelength which reduces the number of exposures required for correction. The output of the estimation algorithm is extended to the higher and lower wavelengths by establishing a functional relationship of the image plane electric field in wavelength. 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 this paper we describe the complex electric field reconstruction from image plane intensity measurements for high contrast coronagraphic imaging. A deformable mirror (DM) surface is modified with pairs of complementary shapes to create diversity in the image plane of the science camera where the intensity of the light is measured. Along with the Electric Field Conjugation correction algorithm, this estimation method has been used in various high contrast imaging testbeds to achieve the best contrasts to date both in narrow and in broad band light. We present the basic methodology of estimation in easy to follow list of steps, present results from HCIT and raise several open questions we are confronted with using this method.

The detection of high contrast companions at small angular separation appears feasible in conventional direct images using the self-calibration properties of interferometric observable quantities. In the high-Strehl regime, available from space borne observatories and using AO in the mid-infrared, quantities comparable to the closurephase that are used with great success in non-redundant masking inteferometry, can be extracted from direct images, even taken with a redundant aperture. These new phase-noise immune observable quantities, called Kernel-phases, are determined a-priori from the knowledge of the geometry of the pupil only. Re-analysis of HST/NICMOS archive and other ground based AO images, using this new Kernel-phase algorithm, demonstrates the power of the method, and its ability to detect companions at the resolution limit and beyond.

An occulter is a spacecraft with a precisely-shaped optical edges which flies in formation with a telescope, blocking light from a star while leaving light from nearby planets unaffected. Using linear optimization, occulters can be designed for use with telescopes over a wide range of telescope aperture sizes, science bands, and starlight suppression levels. It can be shown that this optimization depends primarily on a small number of independent nondimensional parameters, which correspond to Fresnel numbers and physical scales and enter the optimization only as constraints. We show how these can be used to span the parameter space of possible optimized occulters; this data set can then be mined to determine occulter sizes for various mission scenarios and sets of engineering constraints.

We present a starshade error budget with engineering requirements that are well within the current manufacturing and metrology capabilities. The error budget is based on an observational scenario in which the starshade spins about its axis on timescales short relative to the zodi-limited integration time, typically several hours. The scatter from localized petal errors is smoothed into annuli around the center of the image plane, resulting in a large reduction in the background flux variation while reducing thermal gradients caused by structural shadowing. Having identified the performance sensitivity to petal shape errors with spatial periods of 3-4 cycles/petal as the most challenging aspect of the design, we have adopted and modeled a manufacturing approach that mitigates these perturbations with 1-m long precision edge segments positioned using commercial metrology that readily meets assembly requirements. We have performed detailed thermal modeling and show that the expected thermal deformations are well within the requirements as well. We compare the requirements for four cases: a 32 m diameter starshade with a 1.5 m telescope, analyzed at 75 and 90 mas, and a 40 m diameter starshade with a 4 m telescope, analyzed at 60 and 75 mas.

An external occulter precisely flown in formation with a space telescope has been recently studied as a mission scenario for direct imaging of exoplanets. 10^-10 contrast must be attained to permit imaging of the faint reflected light of an Earth-like exoplanet. Here we report on experimental verification of a scaled occulter design that maintains a constant Fresnel number to an equivalent 400 mas space mission in monochromatic light at 632 nm using a diverging beam and an outer mask to suspend the occulter mask. We report contrast in regions of the discovery zone at 4.71 × 10^-10 and suppression in the pupil plane of 3.7 × 10^-7.

High-precision spectrographs play a key role in exoplanet searches using the radial velocity technique. But at the accuracy level of 1 m.s-1, required for super-Earth characterization, stability of fiber-fed spectrograph performance is crucial considering variable observing conditions such as seeing, guiding and centering errors and, telescope vignetting. In fiber-fed spectrographs such as HARPS or SOPHIE, the fiber link scrambling properties are one of the main issues. Both the stability of the fiber near-field uniformity at the spectrograph entrance and of the far-field illumination on the echelle grating (pupil) are critical for high-precision radial velocity measurements due to the spectrograph geometrical field and aperture aberrations. We conducted tests on the SOPHIE spectrograph at the 1.93-m OHP telescope to measure the instrument sensitivity to the fiber link light feeding conditions: star decentering, telescope vignetting by the dome,and defocussing. To significantly improve on current precision, we designed a fiber link modification considering the spectrograph operational constraints. We have developed a new link which includes a piece of octagonal-section fiber, having good scrambling properties, lying inside the former circular-section fiber, and we tested the concept on a bench to characterize near-field and far-field scrambling properties. This modification has been implemented in spring 2011 on the SOPHIE spectrograph fibers and tested for the first time directly on the sky to demonstrate the gain compared to the previous fiber link. Scientific validation for exoplanet search and characterization has been conducted by observing standard stars.

On-going developments on the PERSEE nulling testbench include the realization of a focal plane simulator featuring one central star, an extra-solar planet orbiting around it, and an Exo-Zodiacal Cloud (EZC) surrounding the observed stellar system. PERSEE (Pégase Experiment for Research and Stabilization of Extreme Extinction) is a laboratory testbench jointly developed by a Consortium of six French institutes and companies, incorporating Observatoire de la Côte d'Azur (OCA) who is in charge of the manufacturing and procurement of the future Star and Planet Simulator (SPS). In this communication is presented a complete description of the SPS, including general requirements, techniques employed for simulating the observed planet and EZC, opto-mechanical design and expected performance. The current status of the SPS activities is summarized in the conclusion, pending final integration on the PERSEE test bench in September 2011.

A small fraction of Kepler telescope exposures are rejected because of transient, excess background in the field. The patterns of illumination vary from broad streaks to diffuse patches, sometimes filling the focal plane. Examination of such images and their temporal variation shows that they can be attributed to nearby particles crossing the field-of-view of the telescope. Most of the particles appear to be receding. The visual appearance and frequency are consistent with the "debris storms" reported by STEREO SECCHI observers and which they found to be coincident with meteoroid impacts. In addition, a few events, lasting several hours each, appear to be caused by more distant extended sources, possibly the remains of comet dust trails. The tracking cameras, located at the opposite end from the telescope's entrance, and pointed at roughly right angles to its line-of-sight, also detected moving light sources. Their behavior was consistent with the main telescope sightings. Future missions requiring precise, uninterrupted photometry and pointing may benefit from understanding this phenomenon and mitigating it by design and data analysis.

Nuller coronagraphs such as the Achromatic-Interfero-Coronagraph (AIC) can perfectly cancel the starlight by destructively interfering it with itself, if the star is unresolved and exactly on-axis. Small pointing errors as well as the finite stellar diameter of the targeted star may however greatly degrade the performance of this type of coronagraph. Observed at 600nm with an AIC behind a 10 m telescope, the Sun at 10 pc would present an apparent angular diameter of 0.001" that would induce a star-leakage of 10-6 times the maximum intensity of the star at 0.1". The expected flux ratio between a Sun-like star and an Earth-like planet is however much lower (10^-10 in the visible). We show through an analytical formalism that an apodized nuller coronagraph (ANC) can achieve planet detections with much higher contrasts. Expressions of the local contrast ratio and of the signal-to-noise ratio are derived. We first use for demonstrative purposes Sonine profiles and spheroidal prolate profiles. Concentric ring profiles, obtained through a numerical optimization, are also presented. The efficiency of these 3 types of apodizations is discussed.

The Echelle spectrograph FOCES,1 that was operated at the 2.2m Calar Alto telescope between 1995 and 2009 was moved to the laboratories of Munich University Observatories and is being as a test bed for a number of different stability issues related to high precision radial velocity spectroscopy. We utilize FOCES to study spectrograph stability, illumination stability and fiber transport stability. Results from temperature and pressure stabilization are presented with this paper. We will show, that we reach the requirements set by our model analysis approach presented in [2]. Peak to valley mid term stability of temperature and pressure is as good as 0.002K and 0.02hPa.

Current observations in the context of exoplanet searches with coronagraphic instruments have shown that one of the main limitations to high-contrast imaging is due to residual quasi-static speckles. Speckles look like the image of a planet, but they have a different spectral behavior and are optically coherent with the star. We present two techniques to distinguish a planet from speckles. We are assuming that the optical path can be changed enough so that the speckles will change significantly between each image and therefore our model of each image having an independent source of aberrations (creating a new speckle pattern) from the other images is a good model. In the future, we would like to design and build a testbed suitable for coherent speckle detection studies. There are two techniques we want to apply to create the necessary multiple images with changing speckle patterns. The first is to use images generated using our existing deformable mirror (DM) control algorithm and the second is to put deliberate shapes on the DM to achieve the desired speckle pattern outcome.

The Korea Astronomy and Space Science Institute (KASI) are under development three 1.6m optical telescopes for the Korea Micro-lensing Telescope Network (KMTNet) project. These will be installed at three southern observatories in Chile, South Africa, and Australia by middle 2014 to monitor dense star fields like the Galactic bulge and Large Magellanic Cloud. The primary scientific goal of the project is to discover numerous extra-solar planets using the gravitational micro-lensing technique. We have completed the final design of the telescope. The most critical design issue was wide-field optics. The project science requires the Delivered Image Quality (DIQ) of less than 1.0 arcsec FWHM within 1.2 degree radius FOV, under atmospheric seeing of 0.75 arcsec. We chose the prime-focus configuration and realized the DIQ requirement by using a purely parabolic primary mirror and four corrector lenses with all spherical surfaces. We present design results of the wide-field optics, the primary mirror coating and support, and the focus system with three linear actuators on the head ring.

Detection of transiting exoplanets requires high precision photometry, at the percent level for giant planets and at the 1e-5 level for detection of Earth-like rocky planets. Space provides an ideally stable - but costly - environment for high precision photometry. Achieving high precision photometry on a large number of sources from the ground is scientifically valuable, but also very challenging, due to multiple sources of errors. These errors can be greatly reduced if a large number of small wide field telescopes is used with an adequate data analysis algorithm, and the recent availability of low cost high performance digital single lens reflex (DSLR) cameras thus provides an interesting opportunity for exoplanet transit detection. We have recently assembled a prototype DSLR-based robotic imaging system for astronomy, showing that robotic high imaging quality units can be build at a small cost (under $10000 per deg²m² of etendue), allowing multiple units to be built and operated. We demonstrate that a newly developed data reduction algorithm can overcome detector sampling and color issues, and allow precision photometry with these systems, approaching the limit set by photon noise and scintillation noise - which can both average as the inverse square root of etendue. We conclude that for identification of a large number of exoplanets, a ground-based distributed system consisting of a large number of DSLR-based units is a scientifically valuable cost-effective approach.

The Vector Vortex Coronagraph (VVC) is an attractive internal coronagraph solution to image and characterize exoplanets. It provides four key pillars on which efficient high contrast imaging instruments can be built for ground- and space-based telescopes: small inner working angle, high throughput, clear off-axis discovery space, and simple layout. We present the status of the VVC technology development supported by NASA. We will review recent results of the optical tests of the second-generation topological charge 4 VVC on the actively corrected High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory (JPL). New VVC contrast records have been established.

Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity. The Zodiac II instrument is a 1.1-m diameter SiC telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visiblewavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights within the United States followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

The Observatory of Geneva has designed, built and tested in collaboration with ESO a calibrator system based on a Fabry-Perot (FP) interferometer to explore its potential in the calibration of radial velocity (RV) spectrographs. Today, the RV technique has pushed the planet detection limits down to super-earths but the reach the precision required to detect earth-like planets it is necessary to reach a precision around 1cm s^-1. While a significant part of the error budget is the incompressible photon noise, another part is the noise in the wavelength calibration of the spectrograph. It is to address this problem that we have developed this new device. We have obtained exciting results with the calibrator system demonstrated 10 cm s^-1 stability over one night and 1 m s^-1 over 60 days. By further improving the injection system we are aiming at a 1 m s^-1 repeatability over the long term.

The NASA Exoplanet program and the Cosmic Origins program are exploring technical options to combine the visible to NIR performance requirements of a space coronagraph with the general astrophysics requirements of a space telescope covering the deep UV spectrum. Are there compatible options in terms of mirror coatings and telescope architecture to satisfy both goals? In this paper, we address some of the main concerns, particularly relating to polarization in the visible and throughput in the UV. Telescope architectures employing different coating options compatible with current technology are considered in this trade study.