arXiv subjects

Pierre Baudoz

Publications and source records attributed to Pierre Baudoz.

At least 19 recordsLinked to original sources

arXiv2026

First high-contrast results on THD2 testbed after infrastructure upgrade

We present the first scientific results delivered by the upgraded THD2 high-contrast imaging testbed. We report two advances enabled by its improved stability and broadband performance. First, for the Roman Space Telescope, we demonstrate that Gaussian-shaped diversity probes outperform the baseline sinc probes by reducing non-linearities, supporting higher probe amplitudes, and improving electric field estimation efficiency. These results have led to their prioritization as an enhanced early observation for Roman. Second, within ESA's SUPPPPRESS project, we test new polarization-independent Vector Vortex Coronagraphs and design them to high-contrast performance approaching 1e-10 over a 20% bandwidth. We assess their behavior in narrow- and broadband light with active focal-plane wavefront control. Together, these results show how THD2 strengthens Europe's capability in high-contrast imaging, providing a unique platform reaching contrasts of 1e-8 to 1e-9 for developing next-generation coronagraphic technologies.

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arXiv2026

CATKit2-HCI: a collaborative framework for advancing high-contrast coronagraph testbeds

High-contrast exoplanet imaging requires dedicated laboratory testbeds for the development and validation of coronagraph architectures, wavefront sensing and control methods, calibration strategies, and system-level observing concepts. These testbeds often share similar software needs, yet many tools are developed independently at each institution. The CATKit2-High-Contrast-Imaging collaboration, or CATKit2-HCI, addresses this gap by providing a shared software framework for reusable HCI infrastructure. Built on top of CATKit2, an open-source hardware control and synchronization framework originally developed for the High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed at the Space Telescope Science Institute, CATKit2-HCI provides the collaborative layer for HCI-specific algorithms, calibration tools, diagnostics, visualization, and performance metrics. The collaboration currently includes multiple coronagraph testbeds in the United States and Europe. Its goals are to reduce duplicated software development, improve code quality through shared review, enable more direct comparison of results across facilities, and facilitate the movement of students, postdoctoral researchers, and collaborators between laboratories. We describe the motivation, architecture, collaboration model, shared technical capabilities, and early cross-testbed examples of CATKit2-HCI as a framework for accelerating coronagraph technology development.

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arXiv2026

Enhanced wavefront sensing for the Roman Coronagraph Instrument: Gaussian probes and compact model validation

The Coronagraph Instrument on the Roman Space Telescope will be the first space-based system to demonstrate closed-loop focal-plane wavefront sensing and control, a key step towards the Habitable Worlds Observatory. Beyond the baseline Hybrid Lyot Coronagraph, "enhanced modes" are being developed to improve efficiency and science yield. One such mode uses Gaussian probes for electric field estimation, extending the linear regime and allowing higher probe amplitudes. This may increase signal-to-noise, reduce exposure time, accelerate dark hole convergence, and extend operation to stars as faint as $V\sim5$. For those reasons, it was selected by the Coronagraph Community Participation Program's Hardware Working Group as the first technology demonstration carried out on Roman in early 2027. We present numerical simulations using a noise-free compact software model, which demonstrate the benefits of replacing the nominal probes with Gaussian probes.

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arXiv2026

The MICADO first-light imager for the ELT: first steps of the SCAO system MAIT

MICADO is the ELT first light instrument, an imager working at the diffraction limit of the telescope thanks to two adaptive optics (AO) modes: a single conjugate one (SCAO), available at the instrument first light and developed by the MICADO consortium, and a multi conjugate one (MCAO), developed by the MORFEO consortium. Although the project final design review process is about to be completed, the review board and ESO acknowledged that "the review of the final design can be considered complete for the majority of the MICADO sub-systems" and agreed that MICADO can start manufacturing. For the MICADO SCAO module, we have started the manufacturing of several parts: the majority of the SCAO optics and of the SCAO mechanics, the real-time computer software and the instrument control software. This manufacturing is ordered in several steps to allow the progressive integration of a first full AO close loop with the final SCAO parts. In this contribution, we will focus on the first two steps: on our AO S\'esame bench and the so-called "beta flat configuration". We will present the status of this manufacturing and the first results obtained.

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arXiv2026

The MICADO first light imager for the ELT: the SCAO module AIT in France, from the beta flat configuration towards the flat and final configurations

MICADO is the designated ELT first light instrument, a near-infrared imager working at the diffraction limit of the telescope thanks to a SCAO and an MCAO mode. Since summer 2024, MICADO is in its AIT phase and all MICADO partners are currently integrating their subsystems. The MICADO SCAO module will follow three successive AIT phases in France: the beta flat configuration, the flat configuration and the final configuration. In this contribution I will first present the progress made in the AIT of the beta flat configuration and its closed loop results. I will then present the performed and on-going tasks for the flat and final configurations (manufacturing, delivery and integration of several SCAO subsystems and pieces of software) and the results obtained so far in the flat configuration. I will then conclude with the expected following steps of the SCAO module AIT in Garching.

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arXiv2026

SUPPPPRESS: Prototyping and testing liquid-crystal vector vortex coronagraphs with reduced polarization leakage

The vortex coronagraph is one of the most promising candidates for the Habitable Worlds Observatory (HWO) due to its excellent theoretical performance for an off-axis telescope. A practical realization can be achieved using liquid-crystal polymers to form a vector vortex coronagraph (VVC). Reaching the $10^{-10}$ contrast required for Earth-like planet detection is, however, limited by polarization leakage caused by wavelength-dependent deviations from half-wave retardance. This effect can be mitigated using multi-layer twisted retarders to minimize leakage, and by combining the VVC with multiple polarization gratings (mgVVC) to diffract the polarization leakage out of the science path. We present recent progress within the ESA-funded SUPPPPRESS project, which aims to advance the manufacturing, assembly, and testing of high-performance VVCs. Central singularities of 2 and 6 $\mu$m have been achieved for charge 2 and charge 6 VVCs, respectively, with patterning accuracies better than 1 degree root-mean-square error. Fabrication procedures have been developed to produce individual components with a polarization leakage of $3\times10^{-4}$ over a 10% bandwidth and $8\times10^{-4}$ over a 20% bandwidth. We also report on the development of assembly and alignment procedures for mgVVCs and their metrology. Furthermore, we present initial high-contrast tests at the THD2 bench for both regular VVCs and a double-grating VVC. The double-grating VVC reaches an average contrast between 3 and 10 $\lambda$/D of $2 \times 10^{-8}$ over a small bandwidth and $6\times 10^{-8}$ over a 10% bandwidth. Finally, we report on successful space-environment tests of the assembled liquid-crystal masks.

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arXiv2025

Coherent Differential Imaging of high-contrast extended sources with VLT/SPHERE

High-contrast imaging relies on advanced coronagraphs and adaptive optics (AO) to attenuate the starlight. However, residual aberrations, especially non-common path aberrations between the AO channel and the coronagraph channel, limit the instrument performance. While post-processing techniques such as spectral or angular differential imaging (ADI) can partially address those issues, they suffer from self-subtraction and inefficiencies at small angular separations or when observations are conducted far from transit. We previously demonstrated the on-sky performance of coherent differential imaging (CDI), which offers a promising alternative. It allows for isolating coherent starlight residuals through speckle modulation, which can then be subtracted from the raw images during post-processing. This work aims to validate a CDI method on real science targets, demonstrating its effectiveness in imaging almost face-on circumstellar disks, which are typically challenging to retrieve with ADI. We temporally modulated the speckle field in VLT/SPHERE images, applying small phase offsets on the AO deformable mirror while observing stars surrounded by circumstellar material: HR 4796A, CPD-36 6759, HD 169142, and HD 163296. We hence separated the astrophysical scene from the stellar speckle field, whose lights are mutually incoherent. Combining a dozen of data frames and reference coronagraph point spread functions through a Karhunen-Lo\`eve image projection framework, we recover the circumstellar disks without the artifacts that are usually introduced by common post-processing algorithms (e.g., self-subtraction). The CDI method therefore represents a promising strategy for calibrating the effect of static and quasi-static aberrations in future direct imaging surveys. Indeed, it is efficient, does not require frequent telescope slewing, and does not introduce image artifacts to first order.

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arXiv2025

MIRI-JWST mid-infrared direct imaging of the debris disk of HD106906

We report MIRI-JWST coronagraphic observations at 11.3 and 15.5 mic of the debris disk around the young star HD 106906. The observations were made to characterize the structure, temperature and mass of the disk through the thermal emission of the dust heated by the central star. Another goal was also to constrain the size distribution of the grains. The data were reduced and calibrated using the JWST pipeline. The analysis was based on a forward-modeling of the images using a multiparameter radiative transfer model coupled to an optical code for coronagraphy processing. The disk is clearly detected at both wavelengths. The slight asymmetry is geometrically consistent with the asymmetry observed in the near-IR, but it is inconsistent the brightness distribution. The observed structure is well reproduced with a model of a disk (or belt) with a critical radius 70 au, a mildly inward-increasing density (index 2) and a steeper decrease outward (index -6). This indication of a filled disk inside the critical radius is inconsistent with sculpting from an inner massive planet. The size distribution of the grains that cause the mid-IR emission is well constrained by the flux ratio at the two wavelengths : 0.45 10 mic and 0.65 10 mic for silicate and graphite grains, respectively. The minimum size is consistent with predictions of blowout through radiative pressure. We derive a mass of the dust that causes the mid-IR emission of 3.3 5.0 E3 Mearth. When the larger grains (up to 1 cm) that cause the millimeter emission are included, we extrapolate this mass to 0.10 0.16 Mearth. We point out to that this is fully consistent with ALMA observations of the disk in terms of dust mass and of its millimeter flux. We estimate the average dust temperature in the planetesimal belt to be 74 K, and a temperature range within the whole disk from 40 to 130 K.

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arXiv2025

Extended Linearity in the High-Order Wavefront Sensor for the Roman Coronagraph

Context. The Coronagraphic Instrument (CGI) on the Roman Space Telescope aims for unprecedented contrast for direct imaging of exoplanets, serving as a critical tech demo for future missions like the Habitable Worlds Observatory. This requires advanced wavefront sensing and control (WFS&C), including pair-wise (PW) probing for electric field estimation in the focal plane. Optimizing PW probe designs is vital to enhance performance and reduce overheads. Aims. We investigate different probe designs for PW probing in the context of Roman CGI. We compare classic sinc-sinc-sine probes, previously introduced single-actuator probes, and newly proposed sharp sinc probes in terms of effectiveness in focal-plane modulation, resilience to non-linearities, and overall impact on convergence and contrast. Methods. We conducted experiments on the THD2 testbed, configured to emulate Roman CGI with a custom Hybrid Lyot Coronagraph. We evaluated the three probe designs through WFS&C experiments using PW probing for estimation and electric field conjugation for wavefront correction. Simulations and hardware tests assessed contrast convergence and the impact of non-linear terms at varying probe amplitudes. We also explored low-flux scenarios to demonstrate the use of high-amplitude probes in reducing exposure times or closing the loop on faint targets. Results. Single-actuator probes emerged as the most effective, with faster convergence and reduced non-linear effects at high amplitudes. Sharp sinc probes performed moderately well but were less robust than single actuators. High-amplitude single-actuator probes showed advantages in dark-hole digging under low-flux, through faster iterations without significant degradation in contrast. The THD2 testbed, operating at contrasts analogous to Roman CGI, validated our results and underscored its role as a critical platform for advancing WFS&C techniques.

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arXiv2024

First unambiguous detection of ammonia in the atmosphere of a planetary mass companion with JWST/MIRI coronagraphs

The newly accessible mid-infrared (MIR) window offered by the James Webb Space Telescope (JWST) for exoplanet imaging is expected to provide valuable information to characterize their atmospheres. In particular, coronagraphs on board the JWST Mid-InfraRed instrument (MIRI) are capable of imaging the coldest directly imaged giant planets at the wavelengths where they emit most of their flux. The MIRI coronagraphs have been specially designed to detect the NH3 absorption around 10.5 microns, which has been predicted by atmospheric models. We aim to assess the presence of NH3 while refining the atmospheric parameters of one of the coldest companions detected by directly imaging GJ 504 b. Its mass is still a matter of debate and depending on the host star age estimate, the companion could either be placed in the brown dwarf regime or in the young Jovian planet regime. We present an analysis of MIRI coronagraphic observations of the GJ 504 system. We took advantage of previous observations of reference stars to build a library of images and to perform a more efficient subtraction of the stellar diffraction pattern. We detected the presence of NH3 at 12.5 sigma in the atmosphere, in line with atmospheric model expectations for a planetary-mass object and observed in brown dwarfs within a similar temperature range. The best-fit model with Exo-REM provides updated values of its atmospheric parameters, yielding a temperature of Teff = 512 K and radius of R = 1.08 RJup. These observations demonstrate the capability of MIRI coronagraphs to detect NH3 and to provide the first MIR observations of one of the coldest directly imaged companions. Overall, NH3 is a key molecule for characterizing the atmospheres of cold planets, offering valuable insights into their surface gravity. These observations provide valuable information for spectroscopic observations planned with JWST.

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arXiv2024

The MICADO first light imager for the ELT: Testing the Lyot coronograph prototypes

MICADO, the European Extremely Large Telescope first light imager will feature a dedicated high contrast imaging mode specifically designed for observing and characterizing exoplanets and circumstellar disks. Its improved sensitivity and angular resolution, compared to existing instruments will significantly increase our knowledge on these planetary systems. MICADO will include three classical Lyot coronagraphs, one vector phase-apodized pupil plane (vAPP) and two sparse apertures. After rapidly describing the final design of MICADO high contrast mode, we will describe the current state of development of the coronographic components and the testing of the first Lyot coronagraph prototypes.

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arXiv2024

Polarization effects on high contrast imaging: measurements on THD2 Bench

The spectroscopic study of mature giant planets and low mass planets (Neptune-like, Earth-like) requires instruments capable of achieving very high contrasts ($10^{-10}-10^{-11}$) at short angular separations. To achieve such high performance on a real instrument, many limitations must be overcome: complex component defects (coronagraph, deformable mirror), optical aberrations and scattering, mechanical vibrations and drifts, polarization effects, etc. To study the overall impact on a complete system representative of high contrast instruments, we have developed a test bench at Paris Observatory, called THD2. In this paper, we focus on the polarization effects that are present on the bench which creates differential aberrations between the two linear polarization states. We compare the recorded beam positions of the two polarization states with the predicted from the Goos-H\"anchen and Imbert-Fedorov effects, both of which cause spatial shifts and angular deviations of the beam, longitudinal and transverse respectively. Although these effects have already been studied in the literature from the optical and quantum mechanical points of view, their measurement and impact on a complete optical bench are rather rare, although they are crucial for high-contrast instruments. After describing the Goos-H\"anchen and Imbert-Fedorov effects and estimating their amplitude on the THD2 bench, we present the protocol we used to measure these effects of polarization on the light beam. We compare predictions and measurements and we conclude on the most limiting elements on our bench polarization-wise.

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arXiv2024

The MICADO first light imager for the ELT: Sparse Aperture Masks, design and simulations

MICADO, the European Extremely Large Telescope first light imager will feature a dedicated high contrast imaging mode specifically designed for observing and characterizing exoplanets and circumstellar disks. Two sparse aperture masks (SAM) will be included, consisting of opaque masks with a set of holes arranged in a non-redundant configuration. Pupil masking transforms a monolithic telescope into an interferometer, with the aim of recovering spatial information down to the diffraction limit of the telescope and below, even in the presence of residual aberrations, such as turbulent AO residuals, and non common path aberrations. On the ELT, SAM will enable the detection of features down to 3.3mas in the J band, 12mas in the K band. Two designs have been chosen and will be reviewed, with complementarity in terms of sensitivity and spatial frequency coverage for image reconstruction. In this contribution, the technical choices will be detailed, such as the hole diameter and arrangement, given the technical constraints such as spectral filter bandwidths, detector dimensions, sampling, read-out-noise and frame rate. We will also report on simulations performed to assess the expected capabilities of this mode, with application examples of close companion detection and contrast curves.

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arXiv2024

The MICADO first light imager for the ELT: MISTHIC simulation pipeline for the high contrast mode of MICADO

We present the Python pipeline that was developed to simulate the high contrast mode images of the MICADO instrument. This mode will comprise three classical Lyot coronagraphs with different occulting spot sizes, one vector apodized phase plate, and two sparse aperture masks. One critical aspect of these modes lies in their sensitivity to aberrations, requiring careful integration of non common path aberrations, as well as turbulent adaptive optics (AO) residuals. Besides, they will be operated following a specific observing strategy based on pupil tracking mode. For these reasons, we have developed the MICADO SimulaTor for HIgh Contrast (MISTHIC) pipeline to simulate realistic image cubes and derive the expected performance of these modes. Several sources of aberrations can be included: turbulent AO residuals, but also static or rotating aberrations, amplitude aberrations, simple Zernike screens... Including MICADO's specific features, such as the absence of atmospheric dispersion prior to the coronagraphic focal plane mask, our intent is to make this pipeline available to the community. This tool can be used to prepare scientific observations with the high contrast mode of MICADO, by predicting the performance to be expected within the most realistic assumptions.

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arXiv2024

Unveiling the HD 95086 system at mid-infrared wavelengths with JWST/MIRI

Mid-infrared imaging of exoplanets and disks is now possible with the coronagraphs of the MIRI on the JWST. This wavelength range unveils new features of young directly imaged systems and allows us to obtain new constraints for characterizing the atmosphere of young giant exoplanets and associated disks. These observations aim to characterize the atmosphere of the planet HD 95086 b by adding mid-infrared information so that the various hypotheses about its atmospheric parameters values can be unraveled. Improved images of circumstellar disks are provided. We present the MIRI coronagraphic imaging of the system HD 95086 obtained with the F1065C, F1140, and F2300C filters at central wavelengths of 10.575, 11.3, and 23 microns, respectively. We explored the method for subtracting the stellar diffraction pattern in the particular case when bright dust emitting at short separation is present. Furthermore, we compared different methods for extracting the photometry of the planet. Using the atmospheric models Exo-REM and ATMO, we measured the atmospheric parameters of HD 95086 b. The planet HD 95086 b and the contribution from the inner disk are detected at the two shortest MIRI wavelengths F1065C and F1140C. The outer colder belt is imaged at 23 microns. The mid-infrared photometry provides better constraints on the atmospheric parameters. We evaluate a temperature of 800-1050 K, consistent with one previous hypothesis that only used NIR data. The radius measurement of 1.0-1.14 RJup is better aligned with evolutionary models, but still smaller than predicted. These observations allow us to refute the hypothesis of a warm circumplanetary disk. HD 95086 is one of the first exoplanetary systems to be revealed at mid-infrared wavelengths. This highlights the interests and challenges of observations at these wavelengths.

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arXiv2024

Revisiting the Borde-Traub focal plane wavefront estimation technique for exoplanet direct imaging

Direct imaging of exoplanets relies on complex wavefront sensing and control architectures. In addition to fast adaptive optics systems, most of the future high-contrast imaging instruments will soon be equipped with focal plane wavefront sensing algorithms. These techniques use the science detector to estimate the static and quasi-static aberrations induced by optical manufacturing defects and system thermal variations. Pair-wise probing (PWP) has been the most widely used, especially for space-based application and will be tested at contrast levels of ~1e-9 on-sky along with the future coronagraph instrument onboarding the Roman Space Telescope. This algorithm leans on phase diversities applied on the deformable mirror that are recorded in pairs. A minimum of two pairs of probes are required per bandwidth. An additional unprobed image is also recorded to verify the convergence rate of the correction. Before PWP, Borde & Traub proposed a similar algorithm that takes advantage of the unprobed image in the estimation process to get rid of the pair diversity requirement. In this work, we theoretically show that this latter technique should be more efficient than PWP when the convergence time is not limited by photon noise. We then present its performance and practical limitations on coronagraphic testbeds at JPL and exhibit a first on-sky control of non-common path aberrations with such method on VLT/SPHERE.

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arXiv2024

Prototyping liquid-crystal coronagraphs for exo-Earth imaging

This paper presents initial results from the ESA-funded ``SUPPPPRESS'' project, which aims to develop high-performance liquid-crystal coronagraphs for direct imaging of Earth-like exoplanets in reflected light. The project focuses on addressing the significant challenge of polarization leakage in vector vortex coronagraphs (VVCs). We utilize newly manufactured multi-grating, liquid-crystal VVCs, consisting of a two- or three-element stack of vortex and grating patterns, to reduce this leakage to the $10^{-10}$ contrast level. We detail the experimental setups, including calibration techniques with polarization microscopes and Mueller matrix ellipsometers to enhance the direct-write accuracy of the liquid-crystal patterns. The performance testing of these coronagraph masks will be conducted on the THD2 high-contrast imaging testbed in Paris.

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arXiv2024

Increasing the raw contrast of VLT/SPHERE with dark hole techniques III. Broadband reference differential imaging of HR\,4796 using a four-quadrant phase mask

Imaging exoplanetary systems is essential to characterizing exoplanetary systems and to studying planet-disk interactions to understand planet formation. Such imaging in the visible and near-infrared is challenging because these objects are very faint relative to their star and only fractions of an arcsecond away. Coronagraphic instruments have already allowed the imaging of a few exoplanets, but their performance is limited by wavefront aberrations. Adaptive optics systems partly compensate for the Earth's atmosphere turbulence, but they cannot fully control the wavefront. Some of the starlight leaks through the coronagraph and forms speckles in the image. Focal plane wavefront control, used as a second stage after the adaptive optics system, can minimize the speckle intensity within an area called the dark hole. We demonstrated the on-sky performance of dark hole techniques, pairwise probing coupled with electric field conjugation, using the apodized pupil Lyot coronagraph of the VLT/SPHERE instrument. In this paper, we probe their performance using the SPHERE four-quadrant phase mask coronagraph. We demonstrate the interest of combining dark hole techniques and reference differential imaging (RDI). We create a dark hole on-sky in the narrow band around~$1.7\,\mu$m observing HR\,4796. We then record broadband images of HR\,4796 and a reference star at the H band. The dark hole techniques improve the H-band detection limit by a factor of three. The dark hole is stable from one star to a nearby star enabling RDI. This stability offers two new strategies of observation. First, one can quickly create a dark hole observing a bright star before pointing to a faint target star. Furthermore, one can couple dark hole techniques and RDI. A very interesting point is that the performance of these methods does not depend on the astrophysical signal.

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