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The ALICE program, for Archival Legacy Investigation of Circumstellar Environment, is currently conducting a virtual survey of about 400 stars, by re-analyzing the HST-NICMOS coronagraphic archive with advanced post-processing techniques. We present here the strategy that we adopted to identify detections and potential candidates for follow-up observations, and we give a preliminary overview of our detections. We present a statistical analysis conducted to evaluate the confidence level on these detection and the completeness of our candidate search., Comment: Proc. SPIE 9605, Techniques and Instrumentation for Detection of Exoplanets VII, 96051P

The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop experiment designed to study wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science and Operations Center. The design of JOST reproduces the physics of JWST’s three-mirror anastigmat (TMA) using three custom aspheric lenses. It provides similar quality image as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at 633 nm. An Iris AO segmented mirror stands for the segmented primary mirror of JWST. Actuators allow us to control (1) the 18 segments of the segmented mirror in piston, tip, tilt and (2) the second lens, which stands for the secondary mirror, in tip, tilt and x, y, z positions. We present the full linear control alignment infrastructure developed for JOST, with an emphasis on multi-field wavefront sensing and control. Our implementation of the Wavefront Sensing (WFS) algorithms using phase diversity is experimentally tested. The wavefront control (WFC) algorithms, which rely on a linear model for optical aberrations induced by small misalignments of the three lenses, are tested and validated on simulations.

Direct detection and characterization of mature giant or sub-Neptune exoplanets in the visible will require space- based instruments optimized for high-contrast imaging with contrasts of 10-9. In this context, the coronagraph instrument (CGI) on the Wide-Field Infrared Survey Telescope (WFIRST) will reach raw contrasts of about 10-8 or better using state-of-the-art starlight suppression and wavefront control techniques. A ten-fold contrast improvement is therefore required using post-processing techniques in order to detect 10-9 planets from speckles. Post-processing techniques that are successful on both ground-based and space-based instruments need to be validated at such high contrast levels. In this communication, we investigate speckle subtraction techniques for different observation strategies and hardware parameters on WFIRST-like simulated images in the presence of deformable mirrors and an hybrid lyot coronagraph (HLC). We compare the contrast gain after post-processing in both speckle-noise and photon-noise dominated regimes for two different observing scenarios: the reference star differential imaging (RDI) and the angular differential imaging (ADI). We find that the ADI observing strategy is more robust to speckle and photon noises than the RDI observing strategy, enabling up to a threefold gain with respect to the latter. Thus, we recommend that the telescope be able to roll by at least 13° off nominal. We investigated the impact of spatial sampling on post-processed sensitivity, in the context of design trade studies for the Integral Field Spectrograph (IFS) component of the instrument. Our preliminary results suggest that the spatial sampling can be halved from the baseline sampling rate (~4 lenslets per λ/D) without any degradation in final contrast, thereby reducing the integration time required for spectroscopic characterization. In the speckle-noise dominated regime, we also find that at Nyquist sampling or higher, sub-pixel reference- to-target offsets have a negligible impact on the level of residual speckles after post-processing.

The current generation of ground-based coronagraphic instruments uses deformable mirrors to correct for phase errors and to improve contrast levels at small angular separations. Improving these techniques, several space and ground based instruments are currently developed using two deformable mirrors to correct for both phase and amplitude errors. However, as wavefront control techniques improve, more complex telescope pupil geometries will soon be a limiting factor for these next generation coronagraphic instru- ments. The technique presented in this proceeding, the Active Correction of Aperture Discontinuities method, is taking advantage of the fact that most future coronagraphic instruments will include two deformable mirrors, and is proposing to find the shapes and actuator movements to correct for the effect introduced by these complex pupil geometries. We here present the results of the parametric analysis realized on the WFIRST pupil for which we obtained high contrast levels with several deformable mirror setups (size, separation between them), coronagraphs (Vortex charge 2, vortex charge 4, APLC) and spectral bandwidths. However, because contrast levels and separation are not the only metrics to maximize the scientific return of an instrument, we also included in this study the influence of these deformable mirror shapes on the throughput of the instrument and sensitivity to pointing jitters. Finally, we present results obtained on another potential space based telescope segmented aperture. The main result of this proceeding is that we now obtain comparable performance than the coronagraphs previously designed for WFIRST. First result from the parametric analysis strongly suggest that the 2 deformable mirror set up (size and distance between them) has a important impact on the performance in contrast and throughput of the final instrument., Comment: Proceedings of the SPIE, Volume 9904, id. 99044T 12 pp. (2016)

We discuss new results of coronagraphic simulations demonstrating a novel mode for JWST that utilizes sub-pixel dithered reference images, called Small-Grid Dithers, to optimize coronagraphic PSF subtraction. These sub-pixel dithers are executed with the Fine Steering Mirror under fine guidance, are accurate to ~2-3 milliarcseconds (1-σ/axis), and provide ample speckle diversity to reconstruct an optimized synthetic reference PSF using LOCI or KLIP. We also discuss the performance gains of Small-Grid Dithers compared to the standard undithered scenario, and show potential contrast gain factors for the NIRCam and MIRI coronagraphs ranging from 2 to more than 10, respectively.

Recent efforts combining the optimization techniques of apodized pupil Lyot coronagraphs (APLC) and shaped pupils have demonstrated the viability of a binary-transmission mask architecture for extremely high contrast (10-10) exoplanet imaging. We are now building on those innovations to carry out a survey of Lyot coronagraph performance for large, segmented telescope apertures. These apertures are of the same kind under considera- tion for NASA's Large UV/Optical/IR (LUVOIR) observatory concept. To map the multi-dimensional design parameter space, we have developed a software toolkit to manage large sets of mask optimization programs and execute them on a computing cluster. Here we summarize a preliminary survey of 500 APLC solutions for 4 reference hexagonal telescope apertures. Several promising designs produce annular, 10-10 contrast dark zones down to inner working angle 4λ0=D over a 15% bandpass, while delivering a half-max PSF core throughput of 18%. We also report our progress on devising solutions to the challenges of Lyot stop alignment/fabrication tolerance that arise in this contrast regime.

The James Webb Space Telescopes segmented primary and deployable secondary mirrors will be actively con- trolled to achieve optical alignment through a complex series of steps that will extend across several months during the observatory's commissioning. This process will require an intricate interplay between individual wavefront sensing and control tasks, instrument-level checkout and commissioning, and observatory-level calibrations, which involves many subsystems across both the observatory and the ground system. Furthermore, commissioning will often exercise observatory capabilities under atypical circumstances, such as fine guiding with unstacked or defocused images, or planning targeted observations in the presence of substantial time-variable offsets to the telescope line of sight. Coordination for this process across the JWST partnership has been conducted through the Wavefront Sensing and Control Operations Working Group. We describe at a high level the activities of this group and the resulting detailed commissioning operations plans, supporting software tools development, and ongoing preparations activities at the Science and Operations Center. For each major step in JWST's wavefront sensing and control, we also explain the changes and additions that were needed to turn an initial operations concept into a flight-ready plan with proven tools. These efforts are leading to a robust and well-tested process and preparing the team for an efficient and successful commissioning of JWSTs active telescope.

The WFIRST-AFTA Coronagraph aims at forming direct images and measuring the first spectra of exoplanets in orbit around main sequence stars. An important aspect of the instrument is the ability to remove residual stellar speckles to improve the detectability of such planets. Based on detailed simulations and early laboratory tests, we present here some first estimates of the contrast gain expected from advanced post-processing treatments of AFTA-like coronagraphic images. We further discuss their impact on the overall design of the instrument, including its anticipated observing approach.

Direct detection and characterization of mature giant or sub-Neptunes exoplanets in the visible require space-based instruments optimized for high-contrast imaging with contrasts of 10-9. In this context, the Wide-Field Infrared Survey Telescope - Astrophysics Focused Telescope Assets (WFIRST-AFTA) will reach raw contrasts of about 8×10-9 to 10-9 using state-of-the-art starlight suppression and wavefront control techniques. A ten-fold contrast improvement is therefore expected using post-processing techniques to reduce the speckle noise level to a factor of at least 10 lower in order to distinguish 10-9 planets from speckles. Point spread function (PSF) subtractions have been successfully applied to ground-based and space-based data with contrasts up to 10-6 but performance has yet to be demonstrated at higher contrast levels. We use both a classical PSF subtraction and the Karunhen-Loeve Image Projection (KLIP) algorithm to reduce noise free WFIRST-AFTA-like simulated images in the context of reference star differential imaging (RDI). The two WFIRST-AFTA baseline coronagraphs are considered for this study: the hybrid lyot coronagraph (HLC) for the imaging channel and the shaped-pupil coronagraph (SPC) for the integral field spectrograph channel (IFS). The two reduction methods are compared with respect to the amount and stability of the aberrations for detection in the imaging channel and preliminary spectra extractions are performed for characterization in the IFS channel.

We present the results of ongoing coronagraphic simulation s aimed at designing strategies for optimizing oper-ations of the coronagraphs in the mid-infrared instrument ( MIRI) on-board the James Webb Space Telescope(JWST). In particular, the adverse e ects on the point sprea d function caused by the phase mask coronagraphsand the observatory slew accuracy are known to limit our abil ity to position stars at the center of the coron-agraph. Here, we investigate these two e ects on our ability to perform target acquisition (TA) and considerdi erent scenarios involving single and multiple acquisit ions to mitigate them. We assess the performance of thecoronagraphs under various slew accuracy models as well as n oise sources. In general, we nd that scenarios thatrequire fewer acquisitions yield nal positions with small er dispersions but larger o sets. Our Single TA scenarioyields the best repeatability for all three slew accuracy mo dels that we considered although a dual Twin TAstrategy generally yields more accurate centering. We also investigate the use of the contamination control cover(CCC) inside MIRI during TA of bright objects, and ways to mit igate the resulting latent images when the CCCis not used. Our results are expressed in terms of achieved co ntrast with simple, single reference star subtraction.Given our preliminary prescription for latency, our simula tions suggest that the CCC need not be used exceptfor very bright sources; detailed guidelines will require a dditional information on the latent image decay timescale. Furthermore, we nd that contrast is dependent on the observatory slew accuracy at any wavelength. Thehighest contrast is achieved with the highest slew accuracy model, although the background photon noise limitsthe contrast at longer wavelengths.Keywords: High-Contrast Imaging, Instrumentation, JWST Operations , MIRI

The Gemini Planet Imager (GPI) is a facility extreme-AO high-contrast instrument – optimized solely for study of faint companions – on the Gemini telescope. It combines a high-order MEMS AO system (1493 active actuators), an apodized pupil Lyot coronagraph, a high-accuracy IR post-coronagraph wavefront sensor, and a near-infrared integral field spectrograph. GPI incorporates several other novel features such as ultra-high quality optics, a spatially-filtered wavefront sensor, and new calibration techniques. GPI had first light in November 2013. This paper presnets results of first-light and performance verification and optimization and shows early science results including extrasolar planet spectra and polarimetric detection of the HR4696A disk. GPI is now achieving contrasts approaching 10-6 at 0.5” in 30 minute exposures.

Coronagraphic Target Acquisition (TA) is an important factor that contributes to the contrast performance and typically depends on the coronagraph design. In the case of JWST, coronagraphic TAs rely on measuring the centroid of the star's point spread function away from the focal plane mask, and performing a small angle ma- neuver (SAM), to place the star behind the coronagraphic mask. Therefore, the accuracy of the TA is directly limited by the SAM accuracy. Typically JWST coronagraphic observations will include the subtraction of a reference (either a reference star, or a self-reference after a telescope roll). With such differential measurement, the reproducibility of the TA is a very important factor. We propose a novel coronagraphic observation concept whereby the reference PSF is first acquired using a standard TA, followed by coronagraphic observations of a reference star on a small grid of dithered positions. Sub-pixel dithers (5-10 mas each) provide a small reference PSF library that samples the variations in the PSF as a function of position relative to the mask, thus compen- sating for errors in the TA process. This library can be used for PSF subtraction with a variety of algorithms (e.g; LOCI or KLIP algorithms, Lafreniere et al. 2007; Soummer, Pueyo and Larkin 2012). These sub-pixel dithers are executed under closed-loop fine guidance, unlike a standard SAM that executes the maneuver in coarse point mode, which can result in a temporary target offset of 1 arcsecond and would bring the star out from behind the coronagraphic mask. We discuss and evaluate the performance gains from this observation scenario compared to the standard TA both for MIRI coronagraphs.

The Apodized Pupil Lyot Coronagraph (APLC) is a di_raction suppression system adopted in the baseline of several new and recent high-contrast imaging instruments (Palomar P1640, Gemini Planet Imager, VLT/SPHERE) to enable direct imaging of exoplanets at small angular separations (> 0.2 arcsec) from their host star. This coronagraph combines an entrance pupil apodizer, a hard-edge focal plane mask (FPM) and a Lyot stop in a relayed pupil plane to form the coronagraphic image of an observed star onto a camera located in the image plane. The APLC designs underlying these instruments take advantage of the eigen-properties between entrance pupil and Lyot stop, and rely on prolate apodization to reach a contrast performance of 10 7 over a 20% spectral bandwidth and with a moderate inner working angle (IWA, ~ 5 λ/=D) in the presence of central obstruction and support structures. In this communication we propose novel designs relying on the linearity between the coronagraphic electric field at the science camera and the apodization function. We use this relationship to devise a numerical optimization scheme that extends the APLC performance (contrast, IWA, apodizer through- put, chromaticity) beyond the intrinsic properties of prolate apodizations. We explore the parameter space by considering different aperture geometries, contrast levels, dark-zone size, spectral bandwidth and FPM size. We present the application of these new solutions to the case of the High-Contrast Imager for Complex Aperture Telescopes (HiCAT).

NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.

International audience; The present and next few years will see the arrival of several new coronagraphic instruments dedicated to the detection and characterization of planetary systems. These ground- and space-based instruments (Gemini/GPI, VLT/SPHERE, Subaru/ CHARIS, JWST NIRCam and MIRI coronagraphs among others), will provide a large number of new candidates, through multiple nearby-star surveys and will complete and extend those acquired with current generation instruments (Palomar P1640, VLT/NACO, Keck, HST). To optimize the use of the wealth of data, including non-detection results, the science products of these instruments will require to be shared among the community. In the long term such data exchange will significantly ease companion confirmations, planet characterization via different type of instruments (integral field spectrographs, polarimetric imagers, etc.), and Monte-Carlo population studies from detection and non-detection results. In this context, we initiated a collaborative effort between the teams developing the data reduction pipelines for SPHERE, GPI, and the JWST coronagraphs, and the ALICE (Archival Legacy Investigations of Circumstellar Environment) collaboration, which is currently reprocessing all the HST/NICMOS coronagraphic surveys. We are developing a standard format for the science products generated by high-contrast direct imaging instruments (reduced image, sensitivity limits, noise image, candidate list, etc.), that is directly usable for astrophysical investigations. In this paper, we present first results of this work and propose a preliminary format adopted for the science product. We call for discussions in the high-contrast direct imaging community to develop this effort, reach a consensus and finalize this standard. This action will be critical to enable data interchange and combination in a consistent way between several instruments and to stiffen the scientific production in the community.

We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential Deformable Mirrors to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of Deformable Mirror Surfaces that yield high contrast Point Spread Functions is not linear, and non-linear methods are needed to find the true minimum in the optimization topology. We solve the highly non-linear Monge-Ampere equation that is the fundamental equation describing the physics of phase induced amplitude modulation. We determine the optimum configuration for our two sequential Deformable Mirror system and show that high-throughput and high contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to JWST, ACAD can attain at least 10-7 in contrast and an order of magnitude higher for future Extremely Large Telescopes, even when the pupil features a missing segment" . We show that the converging non-linear mappings resulting from our Deformable Mirror shapes actually damp near-field diffraction artifacts in the vicinity of the discontinuities. Thus ACAD actually lowers the chromatic ringing due to diffraction by segment gaps and strut's while not amplifying the diffraction at the aperture edges beyond the Fresnel regime and illustrate the broadband properties of ACAD in the case of the pupil configuration corresponding to the Astrophysics Focused Telescope Assets. Since details about these telescopes are not yet available to the broader astronomical community, our test case is based on a geometry mimicking the actual one, to the best of our knowledge.

P1640 high contrast imaging system on the Palomar 200 inch Telescope consists of an apodized-pupil Lyot coronagraph, the PALM-3000 adaptive optics (P3K-AO), and P1640 Calibrator (CAL). Science images are recorded by an integral field spectrograph covering J-H bands for detecting and characterizing stellar companions. With aberrations from atmosphere corrected by the P3K-AO, instrument performance is limited mainly by the quasi-static speckles due to noncommon path wavefront aberrations for the light to propagate to the P3K-AO wavefront sensor and to the coronagraph mask. The non-common path wavefront aberrations are sensed by CAL, which measures the post-coronagraph E-field using interferometry, and can be effectively corrected by offsetting the P3K-AO deformable mirror target position accordingly. Previously, we have demonstrated using CAL measurements to correct high order wavefront aberrations, which is directly connected to the static speckles in the image plane. Low order wavefront, on the other hand, usually of larger amplitudes, causes light to leak through the coronagraph making the whole image plane brighter. Knowledge error in low order wavefront aberrations can also affect the estimation of the high order wavefront. Even though, CAL is designed to sense efficiently high order wavefront aberrations, the low order wavefront front can be inferred with less sensitivity. Here, we describe our method for estimating both low and high order wavefront aberrations using CAL measurements by propagating the post-coronagraph E-field to a pupil before the coronagraph. We present the results from applying this method to both simulated and experiment data.

Searching for nearby habitable worlds with direct imaging and spectroscopy will require a telescope large enough to provide angular resolution and sensitivity to planets around a significant sample of stars. Segmented telescopes are a compelling option to obtain such large apertures. However, these telescope designs have a complex geometry (central obstruction, support structures, segmentation) that makes high-contrast imaging more challenging. We are developing a new high-contrast imaging testbed at STScI to provide an integrated solution for wavefront control and starlight suppression on complex aperture geometries. We present our approach for the testbed optical design, which defines the surface requirements for each mirror to minimize the amplitude-induced errors from the propagation of out-of-pupil surfaces. Our approach guarantees that the testbed will not be limited by these Fresnel propagation effects, but only by the aperture geometry. This approach involves iterations between classical ray-tracing optical design optimization, and end-to-end Fresnel propagation with wavefront control (e.g. Electric Field Conjugation / Stroke Minimization). The construction of the testbed is planned to start in late Fall 2013., Proc. of the SPIE 8864, 10 pages, 3 figures, Techniques and Instrumentation for Detection of Exoplanets VI

The Gemini Planet Imager is a next-generation instrument for the direct detection and characterization of young warm exoplanets, designed to be an order of magnitude more sensitive than existing facilities. It combines a 1700-actuator adaptive optics system, an apodized-pupil Lyot coronagraph, a precision interferometric infrared wavefront sensor, and a integral field spectrograph. All hardware and software subsystems are now complete and undergoing integration and test at UC Santa Cruz. We will present test results on each subsystem and the results of end-to-end testing. In laboratory testing, GPI has achieved a raw contrast (without post-processing) of 10-6 5σ at 0.4”, and with multiwavelength speckle suppression, 2x10-7 at the same separation.

Project 1640, a high-contrast spectral-imaging effort involving a coordinated set of instrumentation and software, built at AMNH, JPL, Cambridge and Caltech, has been commissioned and is fully operational. This novel suite of instrumentation includes a 3388+241-actuator adaptive optics system, an optimized apodized pupil Lyot coronagraph, an integral field spectrograph, and an interferometric calibration wave front sensor. Project 1640 is the first of its kind of instrumentation, designed to image and characterize planetary systems around nearby stars, employing a variety of techniques to break the speckle-noise barrier. It is operational roughly one year before any similar project, with the goal of reaching a contrast of 10^(-7) at 1 arcsecond separation. We describe the instrument, highlight recent results, and document on-sky performance at the start of a 3-year, 99-night survey at the Palomar 5-m Hale telescope.

P1640 calibrator is a wavefront sensor working with the P1640 coronagraph and the Palomar 3000 actuator adaptive optics system (P3K) at the Palomar 200 inch Hale telescope. It measures the wavefront by interfering post-coronagraph light with a reference beam formed by low-pass filtering the blocked light from the coronagraph focal plane mask. The P1640 instrument has a similar architecture to the Gemini Planet Imager (GPI) and its performance is currently limited by the quasi-static speckles due to non-common path wavefront errors, which comes from the non-common path for the light to arrive at the AO wavefront sensor and the coronagraph mask. By measuring the wavefront after the coronagraph mask, the non-common path wavefront error can be estimated and corrected by feeding back the error signal to the deformable mirror (DM) of the P3K AO system. Here, we present a first order wavefront estimation algorithm and an instrument calibration scheme used in experiments done recently at Palomar observatory. We calibrate the P1640 calibrator by measuring its responses to poking DM actuators with a sparse checkerboard pattern at different amplitudes. The calibration yields a complex normalization factor for wavefront estimation and establishes the registration of the DM actuators at the pupil camera of the P1640 calibrator, necessary for wavefront correction. Improvement of imaging quality after feeding back the wavefront correction to the AO system demonstrated the efficacy of the algorithm.

Stellar coronagraphs using circular phase masks are promising concepts dedicated to the image suppression of an observed bright star in order to enhance the substellar mass companions present in its vicinity, typically 2 λ/D angular separation. These concepts include a focal plane phase mask which introduces a phase delay on a part of the stellar image. With an adequate choice of the mask parameters (thickness, diameter), the light going through the mask and the light going outside the mask will interfere destructively inside the geometric pupil in the following pupil plane. The light rejected outside this re-imaged pupil will be blocked by a Lyot stop. Typically, the mask physical size is about λF, where F denotes the f-number of the optical system, and the mask thickness depends on the required phase shifting. The contrast provided by these concepts is highly related to the quality of thickness profile of the phase mask and therefore, severe manufacturing tolerances are necessary to reach the theoretical performance of the corresponding coronagraphic system. In 2007, we designed a Roddier & Roddier phase mask with a 65 μm diameter and ordered it to GEPI of Paris Observatory which manufactured it using ion etching process. A roughness of 0.8 nm rms and a transition width of 1% of the mask diameter were measured with a profilometer for this mask showing the good quality of the mask (N'Diaye et al. 2010). We pursue our efforts to design and manufacture high quality masks in collaboration with the firm SILIOS. Several tests of manufacturing procedures are currently realized to reach the best trade-off between mask roughness and mask transition width. These values, measured in our laboratory with a profilometer, allow us to determine the best configuration for fabrication. In addition, by knowing the mask profile, we can estimate theoretically the performance that can be reached.

A starshade with the James Webb Space Telescope (JWST) is the only possible path forward in the next decade to obtain images and spectra of a planet similar to the Earth, to study its habitability, and search for signs of alien life. While JWST was not specifically designed to observe using a starshade, its near-infrared instrumentation is in principle capable of doing so and could achieve major results in the study of terrestrialmass exoplanets. However, because of technical reasons associated with broadband starlight suppression and filter red-leak, NIRSpec would need a slight modification to one of its target acquisition filters to enable feasible observations of Earth-like planets. This upgrade would 1) retire the high risk associated with the effects of the current filter red leak which are difficult to model given the current state of knowledge on instrument stray light and line spread function at large separation angles, 2) enable access to the oxygen band at 0.76 μm in addition to the 1.26 μm band, 3) enable a smaller starshade by relaxing requirements on bandwidth and suppression 4) reduce detector saturation and associated long recovery times. The new filter would not affect neither NIRSpecs scientific performance nor its operations, but it would dramatically reduce the risk of adding a starshade to JWST in the future and enhance the performance of any starshade that is built. In combination with a starshade, JWST could be the most capable and cost effective of all the exoplanet hunting missions proposed for the next decade, including purpose built observatories for medium-size missions.

Starshades have been shown to hold the potential to reveal Earth-like planets around nearby stars and to allow detailed follow-up study including spectroscopy. Ideally this would be performed with a starshade in excess of 50m diameter and a telescope over 4m in diameter. However, such a flagship-class mission is unlikely to be realized in under fifteen years. But much can be accomplished in substantially less expensive missions. I will review the alternatives and provide an assessment of various architectures and what they can accomplish. These alternatives will include using JWST as the telescope, using small dedicated telescopes, and using smaller starshades.

The New Worlds Observer is a flagship-scale terrestrial planet finding and characterizing mission using an external occulter known as a starshade. The starshade is a separate space vehicle from the observing telescope; the starshade performs all the necessary starlight suppression to enable high contrast imaging of terrestrial exo-planets. While effective as a flagship-scale mission designed to fulfill and exceed the requirements of the Terrestrial Planet Finder (TPF) mission, the starshade architecture is flexible and can accommodate a variety of design and cost categories, including working with an existing telescope. We present in this paper an architecture using a starshade with the James Web Space Telescope (JWST), a mission concept we call New Worlds Probe, which can deliver many of the TPF mission requirements for significantly lower mission cost. We give an overview of the science capabilities, the starshade design and technical maturity, and concepts for starshade-JWST cooperative operation.

High contrast imaging is an ongoing theme in the domain of astronomy, both for ground-based and space-based telescopes. Achieving 106 - 107 contrasts expected with GPI and SPHERE or 1010 contrast for space projects, requires extreme wavefront correction as well as good coronagraphic systems. With the testbed located at the Laboratory of Adaptive Optics in Santa Cruz, we statically correct the wavefront to 0.5 nm in band and reach contrast of a few 107 with an Apodized Lyot Coronagraph (APLC). The Electric Field Conjugation (EFC) allows us to further improve on this performance. EFC is a formalism of the correction problem that computes the actuator commands for the deformable mirror (DM) to correct for both amplitude and phase in a pre-defined region in the final image plane. In order to take into account non-common-path errors and potential amplitude aberrations, the proper actuator commands are computed using an image plane-based DM diversity by means of reconstructing the complex electric field. Already successfully tested for space-based telescopes, we here attempt to adapt this method to ground-based observations, using the EFC high contrast solution to record new reference centroids for a Shack-Hartmann wavefront sensor, which in turn can be used to recreate the far-field image. This paper shows results of this first use of the EFC method with an APLC. We achieved 4.108 contrast on a [4-9] λ/d square region. We also show that it can be applied to ground based adaptive optics, using Shack-Hartmann wavefront sensors.

Stellar coronagraphy is a key technology for current and future instruments for exoplanet imaging and spectroscopy, both on the ground and in space. We pursue the research on coronagraphs based on circular phase masks and report in this paper on recent advances in terms of the trade between spectral bandwidth and achievable contrast. Circular phase masks combined with colored apodizations prove to be promising options in such coronagraphic systems to reach high contrast gains within the search area over a wide band of wavelengths.

In this communication we address the problem of post coronagraphic wavefront reconstruction. In high contrast imaging applications it is crucial to estimate the wavefront after the coronagraph, as close as possible to the science camera, in order to minimize non-common path errors. However closing the loop on such a measurement is a difficult exercise since several low order modes have been cancelled by the coronagraphs, thus leading to ill-posed inversion problems. Moreover sensing at the science detector is an intrusive method that disrupts the course of the observations. The Gemini Planet Imager (GPI) calibration system, based on a post-coronagraphic interferometer, provides an estimate of mid to high spatial frequencies aberrations that alleviates these two issues. However such a measurement have an intrinsic limitations that is related to the differential path errors between the two arm of the interferometer. In this paper we show how to devise wavefront reconstruction algorithms that account for these differential path errors. We identify two regimes, relative and absolute wavefront sensing, that depend on the magnitudes of the aberrations and the design of the coronagraph. We illustrate the performances for each regime. Finally we present experimental results obtained during the validation phase of show the results on laboratory data.

The Gemini Planet Imager (GPI) is an extreme AO coronagraphic integral field unit YJHK spectrograph destined for first light on the 8m Gemini South telescope in 2011. GPI fields a 1500 channel AO system feeding an apodized pupil Lyot coronagraph, and a nIR non-common-path slow wavefront sensor. It targets detection and characterizion of relatively young (

High contrast imaging sometimes uses apodized masks in coronagraphs to suppress diffracted starlight from a bright source in order to observe its environs. Continuously graded opacity material and metallic half-tone dots are two possible apodizers fabrication techniques. In the latter approach if dot sizes are comparable to the wavelength of the light, surface plasmon effects can complicate the optical density (OD) vs. superficial dot density relation. OD can also be a complicated function of wavelength. We measured half-tone microdot screens' and continuous materials' transmissions. Our set-up replicated the f/ 64 optical configuration of the Gemini Planet Imager's Apodized Pupil Lyot Coronagraph pupil plane, where we plan to place our pupil plane masks. Our half-tone samples were fabricated with 2, 5, and 10 micron dot sizes, our continuous greyscale was High Energy Electron Beam Sensitive (HEBS) glass (Canyon Materials Inc.). We present optical density (OD) vs. wavelength curves for our half-tone and continuous greyscale samples 1.1 - 2.5 μm wavelength range. Direct measurements of the beam intensity in the far field using a Fourier Transform Infrared Spectrograph on Beamline U4IR at Brookhaven National Laboratory's National Synchrotron Light Source (NSLS) provided transmission spectra of test patches and apodizers. We report the on-axis IR transmission spectra through screens composed of metallic dots that are comparable in size with the wavelength of the light used, over a range of optical densities. We also measured departures from simple theory describing the array of satellite spots created by thin periodic grids in the pupil of the system. Such spots are used for photometry and astrometry in coronagraphic situations. Our results pertain to both ground and space based coronagraphs that use spatially variable attenuation, typically in focal plane or pupil plane masks.

The calibration wavefront system for GPI will measure the complex wavefront at the apodized pupil and provide slow phase corrections to the AO system to mitigate against errors that would cause a loss in contrast. This talk describes both the low-order and high-order sensors in the calibration wavefront sensor and how the information is combined to form the wavefront estimate before the coronagraph. Expected performance for this wavefront sensor will also be described for typical observing scenarios. Finally, we will show labratory results from our calibration testbed that demonstrate the instrument performance at levels commensurate with those required on the GPI instrument.

The James Webb Space Telescope will be an extraordinary observatory, providing a huge range of exciting new astrophysical results. However, by itself it will not be capable of directly imaging planets in the habitable zone of nearby stars, one of the most fascinating goals of astronomy for the coming decade. In this paper we discuss the New Worlds Probe (NWP) concept whereby we use an external occulter (or starshade) to cast a shadow from the star onto the telescope, therefore canceling the direct star light while the light from a planet is not affected. This concept enables JWST to take images and spectra of extrasolar planets with sufficient contrast and inner working angle to be able to discover planets down to the size of the Earth in the habitable zone around nearby stars. JWST’s instruments are appropriate to achieve low resolution spectroscopy (R � 40) of these planets, and address a series of fundamental questions: are there planets in the habitable zone around nearby stars? What is the composition of their atmosphere? What are the brightness and structures of exozodiacal disks around nearby stars? What is the mass and composition of currently known giant planets? In this paper we study the starshade optimization for JWST given the instrumental constraints, and show that the modest optical quality of the telescope at short wavelength does not impact the possibility of using a starshade. We propose a solution to enable imaging and spectroscopy using target acquisition filters. We discuss possible time allocation among science goals based on exposure time estimates and total available observing time. The starshade can be launched up to 3 years after JWST and rendezvous with the telescope in orbit around L2.

An occulter is an instrument designed to suppress starlight by diffraction from its edges; most are designed to be circular, with a set of identical "petals" running around the outside. Proposed space-based occulters are lightweight, deployed screens tens of meters in diameter with challenging accuracy requirements. In this paper we describe the design of an occulter for the THEIA mission concept. THEIA consists of a 4-meter telescope diffraction limited to 300 nm, and a 40-meter external occulter to provide high-contrast imaging. Operating from 250 to 1000 nm, it will provide a rich family of science projects, including exoplanet characterization, ultraviolet spectroscopy, and very wide-field imaging. Originally conceived of as a hybrid system employing both an occulter and internal coronagraph, THEIA now uses a single occulter to achieve all of the starlight suppression but at two different distances from the telescope in order to minimize size and distance. We describe the basic design principles of the THEIA occulter, its final configuration, performance, and sensitivity.

The Gemini Planet Imager (GPI) is a new facility instrument to be commissioned at the 8-m Gemini South telescope in early 2011. It combines of several subsystems including a 1500 subaperture Extreme Adaptive Optics system, an Apodized Pupil Lyot Coronagraph, a near-infrared high-accuracy interferometric wavefront sensor, and an Integral Field Unit Spectrograph, which serves as the science instrument. GPI's main scientific goal is to detect and characterize relatively young ( 5λ/D, without active wavefront control (no deformable mirror). We use Fresnel propagation modeling to analyze the testbed results.

The Gemini Planet Imager (GPI) is a future high-order coronagraphic adaptive optics system optimized for the search and analysis of Jupiter-like exoplanets around nearby young 10-1000Myr stars. In this paper, an on-axis Fresnel wavefront propagation model of GPI is presented. The main goal of this work is to confirm that the current GPI design will reach its 10-7 contrast requirement. The model, assembled using the PROPER IDL library, is used to properly simulate out-of-pupil-plane and finite size optics. A spectral data cube at GPI spectral resolution R=45 in H-band is obtained to estimate the GPI contrast as a function of wavelength. This cube is then used to evaluate the speckle suppression performance of the Simultaneous Spectral Differential Imaging (SSDI) technique. It is shown that GPI should achieve a photon noise limited 10-7 contrast when using a simple SSDI post-processing on an H=5 star and a 1h observing sequence. Finally, a long exposure data cube is obtained by combining the speckle contributions of an average atmosphere and GPI optics. That final long-exposure contrast as a function of wavelength can be used to estimate the GPI exoplanet characterization accuracy, and to evaluate, using Monte-Carlo simulations, the expected exoplanet survey performance.

The Gemini Planet Imager (GPI) is a facility instrument under construction for the 8-m Gemini South telescope. It combines a 1500 subaperture AO system using a MEMS deformable mirror, an apodized-pupil Lyot coronagraph, a high-accuracy IR interferometer calibration system, and a near-infrared integral field spectrograph to allow detection and characterization of self-luminous extrasolar planets at planet/star contrast ratios of 10-7. I will discuss the evolution from science requirements through modeling to the final detailed design, provide an overview of the subsystems and show models of the instrument's predicted performance.

We present testbed results of the Apodized Pupil Lyot Coronagraph (APLC) at the Laboratory for Adaptive Optics (LAO). This coronagraph is being built for the Gemini Planet Imager (GPI). The apodizer component is manufactured with a halftone technique using black chrome microdots on glass. Testing this APLC (like any other coronagraph) requires extremely good wavefront correction, which is obtained to the 1nm RMS level on the Extreme Adaptive Optics (ExAO) visible testbed of the Laboratory Adaptive optics (LAO) at the University of Santa Cruz. With this testbed, we investigated the performance of the APLC coronagraph and more particularly the effect of the apodizer profile accuracy on the contrast. We obtained the first image of a dark zone in a coronagraphic image with a MEMS deformable mirror. Finally, we compare the resulting contrast to predictions made with a wavefront propagation model of the testbed to understand the effects of phase and amplitude errors on the final contrast.

In July 2008, a new integral field spectrograph and a diffraction limited, apodized-pupil Lyot coronagraph was installed behind the adaptive optics system at the Hale 200-inch telescope at Palomar. This instrument serves as the basis of a long-term observational program in high-contrast imaging. The technical goal is to utilize the spectral nature of speckle noise to overcome it. The coronagraph alone will achieve an initial dynamic range of 10-5 at 1", with first light in mid-2008, without speckle noise suppression. Initial work indicates that spectral speckle suppression will provide a factor of 10 to 100 improvement over this. Such sensitivity provides detection and low resolution spectra of young planets of several Jupiter masses around young stars within 25 pc. The spectrograph obtains 32 images across the J and H bands (1.05 - 1.75 mm), with a spectral resolution of 30-100. The image plane is subdivided by a 200 x 200 element micro-lenslet array with a plate scale of 21 mas per lenslet, diffraction-limited at 1.0 mm. Data is collected with a 2048 x 2048 pixel Rockwell Hawaii-II HgCdTe infrared detector cooled with liquid Nitrogen. This system is the first of a new generation of apodized pupil coronagraphs combined with high-order adaptive optics and integral field spectrographs.

The Exo-Planets Imaging Camera and Spectrograph (EPICS), is the Planet Finder Instrument concept for the European Extremely Large Telescope (ELT). The study made in the frame of the OWL 100-m telescope concept is being up-dated in direct relation with the re-baselining activities of the European Extremely Large Telescope.

This communication deals with apodization and coronagraphy. For apodization alone, we present analytical studies of point spread functions obtained with a rectangular or a circular telescope apodized by cross-linear or circular prolate spheroidal functions, respectively. Results are compared with sonine apodizations investigated by Nisenson and Papaliolios (2001) for the Apodized Square Aperture project. For coronagraphy, prolate functions are the optimal apodizers for rectangular and circular apertures. With the Roddier & Roddier phase mask technique, these apodizations can produce a total extinction of the star light. For Lyot coronagraphy, the extinction, not complete, is surprisingly good for a reasonable mask size. A comparison between coronagraphy and apodization alone for different telescope aperture shape is in favor to the use of a coronagraph with a circular aperture.