Search

METIS is one of the first three instruments for the ELT, Europe’s next-generation ground-based telescope. It will offer imaging, coronagraphy and spectroscopy in the L, M and N bands for general-purpose science in astrophysics. Among its main science drivers are circumstellar disks and extrasolar planets observations, which requires demanding high contrast imaging techniques. In that framework, METIS will be equipped with state-of-the-art phase mask coronagraphs: Apodizing Phase Plate (APP) and Annular Grooves Phase Mask (AGPM). Manufacturing the AGPM coronagraphs is a complex process that requires performance assessment with specific testing before implementation into the instrument. At Department of Astrophysics (CEA Saclay, France), responsible for the testing of the N-band AGPMs, a previously available test bench with a telescope simulator and cryogenic facility has been upgraded to comply with the AGPM tests requirements. This paper presents these requirements and describes the test bench design adopted. Then, based on preliminary results, we discuss the original solutions that permitted to reach our goals.

The planet detection thresholds of space-based coronagraphs are predicted to lie within an order of magnitude from their theoretical (shot-noise) limits. Ground-based telescopes, on the other hand, are limited by larger systematic uncertainties in the point spread function (PSF) of the residual light which rapidly fluctuates due to atmospheric turbulence. The PSF is affected by Adaptive Optics (AO) which reduce the intensity of the speckles but also make them less predictable. Although not a common practice, it is possible to take millisecond exposures of the so-called “frozen” speckles and record the history of AO controls, in which case the collected data resembles that of simulated space coronagraphs. In this work we use the HEEPS simulation of the EELT/METIS to assess the applicability of this newly-developed space-oriented approach to ground-based postprocessing. Unlike intensity-based algorithms, this method formulates the estimation problem in terms of the electric field of the speckles and therefore can incorporate controls history and various temporal models of the electric field variations. In our simulations, we artificially introduced small deformable mirror (DM) probes on top of AO controls, and achieved a post-processing error lower by a factor of 2 than that of Angular Differential Imaging (ADI). However, our attempt at incorporating the AO history without DM probes, has so far resulted in higher errors than ADI.

Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of METIS. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the new Earths in the $\alpha$ Cen Region (NEAR) experiment with the VLT/VISIR instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to $0.015 \lambda/D$ rms over 4h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations., Comment: Published in JATIS. This version is the manuscript resubmitted before acceptance, 30 pages, 14 figures

We successfully rapid-prototyped a mostly off-the-shelf, partially 3D-printed pathfinder version of an integral field spectrograph (IFS) in order to compress the design/build/test schedule of a final, mostly-custom IFS, by accelerating the start date of data pipeline development, thus allowing this development to progress in parallel with the design, procurement, fabrication, and alignment of the final IFS version. This parallel-path development schedule enabled us to successfully design, build, align, test, and extract a data cube from the new IFS within only 1 year, even in the face of several design setbacks. We have begun using the now-functional IFS for development of IFS sensing and control algorithms, and have also begun implementing motorized alignment upgrades that enable the systematic characterization of the tolerance (or required compensation) of its data cube extraction to misaligned images, in support of NASA’s WFIRST and PISCES IFS.

Future space-based observatories such as WFIRST will be equipped with high contrast imaging instruments designed to study extrasolar planets and disks in the absence of atmospheric perturbations. One of the most efficient techniques to achieve this goal is the combination of wavefront control and broadband coronagraphy. Being able to achieve a high contrast over a wide spectral bandwidth allows us to characterize the chemical composition of exoplanet atmospheres using an integral field spectrograph (IFS). In this paper, we report on the development of such an IFS for the High Contrast Imaging Lab (HCIL) at Princeton University, downstream of a Shaped Pupil coronagraph. Our final lensletbased design calls for the light in an 18% band around 660 nm to be dispersed with a spectral resolution of 50. We also present our new laboratory control software written in Python, allowing the import of open-source packages such as CRISPY to ultimately reconstruct 3D datacubes from IFS spatio-spectral science images. Finally, we show and discuss our preliminary first light results, reaching a contrast of ~10-5 using in-house focal-plane wavefront control and estimation algorithms with two deformable mirrors.

The Wide Field Infrared Survey Telescope (WFIRST) mission, scheduled for launch in the mid-2020s will perform exoplanet science via both direct imaging and a microlensing survey. An internal coronagraph is planned to perform starlight suppression for exoplanet imaging, but an external starshade could be used to achieve the required high contrasts with potentially higher throughput. This approach would require a separately-launched occulter spacecraft to be positioned at exact distances from the telescope along the line of sight to a target star system. We present a detailed study to quantify the Δv requirements and feasibility of deploying this additional spacecraft as a means of exoplanet imaging. The primary focus of this study is the fuel use of the occulter while repositioning between targets. Based on its design, the occulter is given an offset distance from the nominal WFIRST halo orbit. Target star systems and look vectors are generated using Exoplanet Open-Source Imaging Simulator (EXOSIMS); a boundary value problem is then solved between successive targets. On average, 50 observations are achievable with randomly selected targets given a 30-day transfer time. Individual trajectories can be optimized for transfer time as well as fuel usage to be used in mission scheduling. Minimizing transfer time reduces the total mission time by up to 4.5 times in some simulations before expending the entire fuel budget. Minimizing Δv can generate starshade missions that achieve over 100 unique observations within the designated mission lifetime of WFIRST.

Context. The Annular Groove Phase Mask (AGPM) is one possible implementation of the vector vortex coronagraph, where the helical phase ramp is produced by a concentric subwavelength grating. For several years, we have been manufacturing AGPMs by etching gratings into synthetic diamond substrates using inductively coupled plasma etching. Aims. We aim to design, fabricate, optimize, and evaluate new L-band AGPMs that reach the highest possible coronagraphic performance, for applications in current and forthcoming infrared high-contrast imagers. Methods. Rigorous coupled wave analysis (RCWA) is used for designing the subwavelength grating of the phase mask. Coronagraphic performance evaluation is performed on a dedicated optical test bench. The experimental results of the performance evaluation are then used to accurately determine the actual profile of the fabricated gratings, based on RCWA modeling. Results. The AGPM coronagraphic performance is very sensitive to small errors in etch depth and grating profile. Most of the fabricated components therefore show moderate performance in terms of starlight rejection (a few 100:1 in the best cases). Here we present new processes for re-etching the fabricated components in order to optimize the parameters of the grating and hence significantly increase their coronagraphic performance. Starlight rejection up to 1000:1 is demonstrated in a broadband L filter on the coronagraphic test bench, which corresponds to a raw contrast of about 1e-5 at two resolution elements from the star for a perfect input wave front on a circular, unobstructed aperture. Conclusions. Thanks to their exquisite performance, our latest L-band AGPMs are good candidates for installation in state-of-the-art and future high-contrast thermal infrared imagers, such as METIS for the E-ELT., Comment: Accepted for publication in A&A

We report on our ongoing development of EXOSIMS and mission simulation results for WFIRST. We present the interface control and the modular structure of the software, along with corresponding prototypes and class definitions for some of the software modules. More specifically, we focus on describing the main steps of our high-fidelity mission simulator EXOSIMS, i.e., the completeness, optical system and zodiacal light modules definition, the target list module filtering, and the creation of a planet population within our simulated universe module. For the latter, we introduce the integration of a recent mass-radius model from the FORECASTER software. We also provide custom modules dedicated to WFIRST using both the Hybrid Lyot Coronagraph (HLC) and the Shaped Pupil Coronagraph (SPC) for detection and characterization, respectively. In that context, we show and discuss the results of some preliminary WFIRST simulations, focusing on comparing different methods of integration time calculation, through ensembles (large numbers) of survey simulations.

On March 2015 an L'-band vortex coronagraph based on an Annular Groove Phase Mask made up of a diamond sub-wavelength grating was installed on NIRC2 as a demonstration project. This vortex coronagraph operates in the L' band not only in order to take advantage from the favorable star/planet contrast ratio when observing beyond the K band, but also to exploit the fact that the Keck II Adaptive Optics (AO) system delivers nearly extreme adaptive optics image quality (Strehl ratios values near 90%) at 3.7μm. We describe the hardware installation of the vortex phase mask during a routine NIRC2 service mission. The success of the project depends on extensive software development which has allowed the achievement of exquisite real-time pointing control as well as further contrast improvements by using speckle nulling to mitigate the effect of static speckles. First light of the new coronagraphic mode was on June 2015 with already very good initial results. Subsequent commissioning nights were interlaced with science nights by members of the VORTEX team with their respective scientific programs. The new capability and excellent results so far have motivated the VORTEX team and the Keck Science Steering Committee (KSSC) to offer the new mode in shared risk mode for 2016B.

For several years, we have been developing vortex phase masks based on sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto diamond substrates, these AGPMs are currently designed to be used in the thermal infrared (ranging from 3 to 13 {\mu}m). Our AGPMs were first installed on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and Keck/NIRC2 in 2015. In this paper, we review the development, commissioning, on-sky performance, and early scientific results of these new coronagraphic modes and report on the lessons learned. We conclude with perspectives for future developments and applications., Comment: To appear in SPIE proceedings vol. 9908

The Annular Groove Phase Mask (AGPM) is a vectorial vortex phase mask. It acts as a half-wave plate with a radial fast axis orientation operating in the mid infrared domain. When placed at the focus of a telescope element provides a continuous helical phase ramp for an on axis sources, which creates the orbital angular momentum. Thanks to that phase, the intensity of the central source is canceled by a down-stream pupil stop, while the off axis sources are not affected. However due to experimental conditions the nulling is hardly perfect. To improve the null, a Mach-Zehnder interferometer containing Dove prisms differently oriented can be proposed to sort out light based on its orbital angular momentum (OAM). Thanks to the differential rotation of the beam, a {\pi} phase shift is achieved for the on axis light affected by a non zero OAM. Therefore the contrast between the star and its faint companion is enhanced. Nevertheless, due the Dove prisms birefringence, the performance of the interferometer is relatively poor. To solve this problem, we propose to add a birefringent wave-plate in each arm to compensate this birefringence. In this paper, we will develop the mathematical model of the wave front using the Jones formalism. The performance of the interferometer is at first computed for the simple version without the birefringent plate. Then the effect of the birefringent plate is be mathematically described and the performance is re-computed.

The mid-infrared region is well suited for exoplanet detection thanks to the reduced contrast between the planet and its host star with respect to the visible and near-infrared wavelength regimes. This contrast may be further improved with Vector Vortex Coronagraphs (VVCs), which allow us to cancel the starlight. One flavour of the VVC is the AGPM (Annular Groove Phase Mask), which adds the interesting properties of subwavelength gratings (achromaticity, robustness) to the already known properties of the VVC. In this paper, we present the optimized designs, as well as the expected performances of mid-IR AGPMs etched onto synthetic diamond substrates, which are considered for the E-ELT/METIS instrument., Comment: 8 pages, 5 figures, Proc. of SPIE Vol. 9147 (2014)

The subwavelength grating vortex coronagraph (SGVC) is a focal-planespiral-like phase mask whose key benefit is to allow high contrast imaging atsmall angles. Directly etched onto a CVD diamond substrate, it is well suitedto perform in the mid-infrared domain. It provides a continuous helicalphase ramp with a dark singularity in its center, and is characterized by itsnumber of phase revolutions, called the topological charge. Over the pasttwo years, we have manufactured several charge-2 SGVCs (a.k.a. annulargroove phase masks) and successfully demonstrated their performanceson 10-m class telescopes (LBT, VLT/NaCo, VLT/VISIR). To prevent stellarleakage on future 30-m class telescopes (E-ELT, TMT, GMT), a broaderoff-axis extinction is required, which can be achieved by increasing thetopological charge. We have recently proposed an original design for acharge-4 SGVC allowing less starlight to leak through the coronagraph, atthe cost of a degraded inner working angle. In this talk, we report on ourlatest development of higher charge SGVCs. From 3D rigorous numericalsimulations using a finite-difference time-domain (FDTD) algorithm, weConference 9605: Techniques and Instrumentationfor Detection of Exoplanets VIIR eturn to Contents +1 360 676 3290 · help@spie.org 647have derived a family of coronagraphs with higher topological charge(SGVC4/6/8). Our new optimization method addresses the principallimitation of such space-variant polarization state manipulation, i.e., theinconvenient discontinuities in the discrete grating pattern. The resultinggratings offer improved precision to the phase modulation compared toprevious designs. Finally, we present our preliminary manufacturing andmetrology results for infrared components down to the K-band.

(abridged) Extreme adaptive optics (XAO) encounters severe difficulties to cope with the high speed (>1kHz), high accuracy and high order requirements for future extremely large telescopes. An innovative high order adaptive optics system using a self-referenced Mach-Zehnder wavefront sensor (MZWFS) allows counteracting these limitations. This sensor estimates very accurately the wavefront phase at small spatial scale by measuring intensity differences between two outputs, with a $\lambda /4$ path length difference between its two legs, but is limited in dynamic range due to phase ambiguity. During the past few years, such an XAO system has been studied by our team in the framework of 8-meter class telescopes. In this work, we report on our latest results with the XAO testbed recently installed in our lab, and dedicated to high contrast imaging with 30m-class telescopes (such as the E-ELT or the TMT). After reminding the principle of a MZWFS and describing the optical layout of our experiment, we will show the results of the assessment of the woofer-tweeter phase correctors, i.e., a Boston Micromachine continuous membrane deformable mirror (DM) and a Boulder Nonlinear Systems liquid crystal spatial light modulator (SLM). In particular, we will detail the calibration of the DM using Zygo interferometer metrology. Our method consists in the precise measurement of the membrane deformation while applying a constant deformation to 9 out of 140 actuators at the same time. By varying the poke voltage across the DM operating range, we propose a simple but efficient way of modeling the DM influence function using a Gaussian model. Finally, we show the DM flattening on the MZWFS allowing to compensate for low order aberrations., Comment: To appear in SPIE proceedings vol. 9617

We present methods for optimizing pupil and focal plane optical elements that improve the performance of vortex coronagraphs on telescopes with obstructed or segmented apertures. Phase-only and complex masks are designed for the entrance pupil, focal plane, and the plane of the Lyot stop. Optimal masks are obtained using both analytical and numerical methods. The latter makes use of an iterative error reduction algorithm to calculate "correcting" optics that mitigate unwanted diffraction from aperture obstructions. We analyze the achieved performance in terms of starlight suppression, contrast, off-axis image quality, and chromatic dependence. Manufacturing considerations and sensitivity to aberrations are also discussed. This work provides a path to joint optimization of multiple coronagraph planes to maximize sensitivity to exoplanets and other faint companions.

The vortex coronagraph is an optical instrument that precisely removes on-axis starlight allowing for high contrast imaging at small angular separation from the star, thereby providing a crucial capability for direct detection and characterization of exoplanets and circumstellar disks. Telescopes with aperture obstructions, such as secondary mirrors and spider support structures, require advanced coronagraph designs to provide adequate starlight suppression. We introduce a phase-only Lyot-plane optic to the vortex coronagraph that offers improved contrast performance on telescopes with complicated apertures. Potential solutions for the European Extremely Large Telescope (E-ELT) are described and compared. Adding a Lyot-plane phase mask relocates residual starlight away from a region of the image plane thereby reducing stellar noise and improving sensitivity to off-axis companions. The phase mask is calculated using an iterative phase retrieval algorithm. Numerically, we achieve a contrast on the order of $10^{-6}$ for a companion with angular displacement as small as $4~\lambda/D$ with an E-ELT type aperture. Even in the presence of aberrations, improved performance is expected compared to either a conventional vortex coronagraph or optimized pupil plane phase element alone., Comment: 6 pages, 7 figures, Accepted for publication in A&A

(abridged) Vortex coronagraphs are among the most promising solutions to perform high contrast imaging at small angular separations. They feature a very small inner working angle, a clear 360 degree discovery space, have demonstrated very high contrast capabilities, are easy to implement on high-contrast imaging instruments, and have already been extensively tested on the sky. Since 2005, we have been designing, developing and testing an implementation of the charge-2 vector vortex phase mask based on concentric subwavelength gratings, referred to as the Annular Groove Phase Mask (AGPM). Science-grade mid-infrared AGPMs were produced in 2012 for the first time, using plasma etching on synthetic diamond substrates. They have been validated on a coronagraphic test bench, showing broadband peak rejection up to 500:1 in the L band, which translates into a raw contrast of about $6\times 10^{-5}$ at $2 \lambda/D$. Three of them have now been installed on world-leading diffraction-limited infrared cameras (VLT/NACO, VLT/VISIR and LBT/LMIRCam). During the science verification observations with our L-band AGPM on NACO, we observed the beta Pictoris system and obtained unprecedented sensitivity limits to planetary companions down to the diffraction limit ($0.1''$). More recently, we obtained new images of the HR 8799 system at L band during the AGPM first light on LMIRCam. After reviewing these first results obtained with mid-infrared AGPMs, we will discuss the short- and mid-term goals of the on-going VORTEX project, which aims to improve the performance of our vortex phase masks for future applications on second-generation high-contrast imagers and on future extremely large telescopes (ELTs)., Comment: To appear in SPIE proceedings vol. 9148

In this paper, we present the infrared coronagraphic test bench of the University of Li\`ege named VODCA (Vortex Optical Demonstrator for Coronagraphic Applications). The goal of the bench is to assess the performances of the Annular Groove Phase Masks (AGPMs) at near- to mid-infrared wavelengths. The AGPM is a subwavelength grating vortex coronagraph of charge two (SGVC2) made out of diamond. The bench is designed to be completely achromatic and will be composed of a super continuum laser source emitting in the near to mid-infrared, several parabolas, diaphragms and an infrared camera. This way, we will be able to test the different AGPMs in the M, L, K and H bands. Eventually, the bench will also allow the computation of the incident wavefront aberrations on the coronagraph. A reflective Lyot stop will send most of the stellar light to a second camera to perform low-order wavefront sensing. This second system coupled with a deformable mirror will allow the correction of the wavefront aberrations. We also aim to test other pre- and/or post-coronagraphic concepts such as optimal apodization.

One possible solution to achieve high contrast direct imaging at a small inner working angle (IWA) is to use a vector vortex coronagraph (VVC), which provides a continuous helical phase ramp in the focal plane of the telescope with a phase singularity in its center. Such an optical vortex is characterized by its topological charge, i.e., the number of times the phase accumulates 2{\pi} radians along a closed path surrounding the singularity. Over the past few years, we have been developing a charge-2 VVC induced by rotationally symmetric subwavelength gratings (SGVC2), also known as the Annular Groove Phase Mask (AGPM). Since 2013, several SGVC2s (or AGPMs) were manufactured using synthetic diamond substrate, then validated on dedicated optical benches, and installed on 10-m class telescopes. Increasing the topological charge seems however mandatory for cancelling the light of bright stars which will be partially resolved by future Extremely Large Telescopes in the near-infrared. In this paper, we first detail our motivations for developing an SGVC4 (charge 4) dedicated to the near-infrared domain. The challenge lies in the design of the pattern which is unrealistic in the theoretically perfect case, due to state-of-the-art manufacturing limitations. Hence, we propose a new realistic design of SGVC4 with minimized discontinuities and optimized phase ramp, showing conclusive improvements over previous works in this field. A preliminary validation of our concept is given based on RCWA simulations, while full 3D finite-difference time-domain simulations (and eventually laboratory tests) will be required for a final validation., Comment: 9 pages

Phase-mask coronagraphs are known to provide high contrast imaging capabilities while preserving a small inner working angle, which allows searching for exoplanets or circumstellar disks with smaller telescopes or at longer wavelengths. The AGPM (Annular Groove Phase Mask, Mawet et al. 2005) is an optical vectorial vortex coronagraph (or vector vortex) induced by a rotationally symmetric subwavelength grating (i.e. with a period smaller than {\lambda}/n, {\lambda} being the observed wavelength and n the refractive index of the grating substrate). In this paper, we present our first mid- infrared AGPM prototypes imprinted on a diamond substrate. We firstly give an extrapolation of the expected coronagraph performances in the N-band (~10 {\mu}m), and prospects for down-scaling the technology to the most wanted L- band (~3.5 {\mu}m). We then present the manufacturing and measurement results, using diamond-optimized microfabrication techniques such as nano-imprint lithography (NIL) and reactive ion etching (RIE). Finally, the subwavelength grating profile metrology combines surface metrology (scanning electron microscopy, atomic force microscopy, white light interferometry) with diffractometry on an optical polarimetric bench and cross correlation with theoretical simulations using rigorous coupled wave analysis (RCWA)., Comment: 10 pages

In November 2012, we installed an L-band annular groove phase mask (AGPM) vector vortex coronagraph (VVC) inside NACO, the adaptive optics camera of ESO’s Very Large Telescope. The mask, made out of diamond subwavelength gratings has been commissioned, science qualified, and is now offered to the community. Here we report ground-breaking on-sky performance levels in terms of contrast, inner working angle, and discovery space. This new practical demonstration of the VVC, coming a few years after Palomar’s and recent record-breaking lab experiments in the visible (E. Serabyn et al. 2013, these proceedings), shows once again that this new-generation coronagraph has reached a high level of maturity.

Coronagraphy is a powerful technique to achieve high contrast imaging and hence to image faint companions around bright targets. Various concepts have been used in the visible and near-infrared regimes, while coronagraphic applications in the mid-infrared remain nowadays largely unexplored. Vector vortex phase masks based on concentric subwavelength gratings show great promise for such applications. We aim at producing and validating the first high-performance broadband focal plane phase mask coronagraphs for applications in the mid-infrared regime, and in particular the L band with a fractional bandwidth of ~16% (3.5-4.1 \mu m). Based on rigorous coupled wave analysis, we designed an annular groove phase mask (AGPM) producing a vortex effect in the L band, and etched it onto a series of diamond substrates. The grating parameters were measured by means of scanning electron microscopy. The resulting components were then tested on a mid-infrared coronagraphic test bench. A broadband raw null depth of 2 x 10^{-3} was obtained for our best L-band AGPM after only a few iterations between design and manufacturing. This corresponds to a raw contrast of about 6 x 10^{-5} (10.5 mag) at 2\lambda/D. This result is fully in line with our projections based on rigorous coupled wave analysis modeling, using the measured grating parameters. The sensitivity to tilt and focus has also been evaluated. After years of technological developments, mid-infrared vector vortex coronagraphs finally become a reality and live up to our expectations. Based on their measured performance, our L-band AGPMs are now ready to open a new parameter space in exoplanet imaging at major ground-based observatories., Comment: 8 pages, 11 figures

Context. High contrast imaging has thoroughly combed through the limited search space accessible with first-generation ground-based adaptive optics instruments and the Hubble Space Telescope. Only a few objects were discovered, and many non-detections reported and statistically interpreted. The field is now in need of a technological breakthrough. Aim. Our aim is to open a new search space with first-generation systems such as NACO at the Very Large Telescope, by providing ground-breaking inner working angle (IWA) capabilities in the L' band. The L' band is a sweet spot for high contrast coronagraphy since the planet-to-star brightness ratio is favorable, while the Strehl ratio is naturally higher. Methods. An annular groove phase mask (AGPM) vector vortex coronagraph optimized for the L' band, made from diamond subwavelength gratings was manufactured and qualified in the lab. The AGPM enables high contrast imaging at very small IWA, potentially being the key to unexplored discovery space. Results. Here we present the installation and successful on-sky tests of an L'-band AGPM coronagraph on NACO. Using angular differential imaging, which is well suited to the rotational symmetry of the AGPM, we demonstrated a \Delta L' > 7.5 mag contrast from an IWA ~ 0".09 onwards, during average seeing conditions, and for total integration times of a few hundred seconds., Comment: 4 pages, 4 figures

In recent years, phase mask coronagraphy has become increasingly efficient in imaging the close environment of stars, enabling the search for exoplanets and circumstellar disks. Coronagraphs are ideally suited instruments, characterized by high dynamic range imaging capabilities, while preserving a small inner working angle. The AGPM (Annular Groove Phase Mask, Mawet et al. 2005) consists of a vector vortex induced by a rotationally symmetric subwavelength grating. This technique constitutes an almost unique solution to the achromatization at longer wavelengths (mid-infrared). For this reason, we have specially conceived a mid-infrared AGPM coronagraph for the forthcoming upgrade of VISIR, the mid-IR imager and spectrograph on the VLT at ESO (Paranal), in collaboration with members of the VISIR consortium. The implementation phase of the VISIR Upgrade Project is foreseen for May-August 2012, and the AGPM installed will cover the 11-13.2 {\mu}m spectral range. In this paper, we present the entire fabrication process of our AGPM imprinted on a diamond substrate. Diamond is an ideal material for mid-infrared wavelengths owing to its high transparency, small dispersion, extremely low thermal expansion and outstanding mechanical and chemical properties. The design process has been performed with an algorithm based on the rigorous coupled wave analysis (RCWA), and the micro-fabrication has been carried out using nano-imprint lithography and reactive ion etching. A precise grating profile metrology has also been conducted using cleaving techniques. Finally, we show the deposit of fiducials (i.e. centering marks) with Aerosol Jet Printing (AJP). We conclude with the ultimate coronagraph expected performances., Comment: 9 pages

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.

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster, ...), it is possible via numerical lens inversion to retrieve the real source image, taking full advantage of the magnifying power of the cosmic lens. This has been achieved in the past for several remarkable gravitational lens systems. Instead, we propose here to invert an observed multiply imaged source directly at the telescope using an ad hoc optical instrument which is described in the present paper. Compared to the previous method, this should allow one to detect fainter source features as well as to use such an optimal gravitational lens telescope to explore even fainter objects located behind and near the lens. Laboratory and numerical experiments illustrate this new approach.

In this paper, we present a solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out of diamond. We use the rigorous coupled wave analysis to design the gratings. Our analysis shows that diamond, besides its outstanding physical and mechanical properties, is a suitable substrate to manufacture mid-infrared HWPs, thanks to its high refractive index, which allows etching SWGs with lower aspect ratio. Based on our optimized design, we manufactured a diamond HWP for the 11-13.2 μm region, with an estimated mean retardance ~3.143±0.061 rad (180.08±3.51°). In addition, an antireflective grating was etched on the backside of the wave plate, allowing a total transmittance between 89% and 95% over the band.