Dr. Marie Ygouf Profile

Dr. Marie Ygouf

Technologist at Jet Propulsion Lab

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Author

Publications (22)

SPIE Journal Paper | 20 September 2024 Open Access

Current laboratory performance of starlight suppression systems and potential pathways to desired Habitable Worlds Observatory exoplanet science capabilities

Bertrand Mennesson, Ruslan Belikov, Emiel Por, Eugene Serabyn, Garreth Ruane, A. J. Eldorado Riggs, Dan Sirbu, Laurent Pueyo, Rémi Soummer, Jeremy Kasdin, Stuart Shaklan, Byoung-Joon Seo, Christopher Stark, Eric Cady, Pin Chen, Brendan Crill, Kevin Fogarty, Alexandra Greenbaum, Olivier Guyon, Roser Juanola-Parramon, Brian Kern, John Krist, Bruce Macintosh, David Marx, Dimitri Mawet, Camilo Mejia Prada, Rhonda Morgan, Bijan Nemati, Leonid Pogorelyuk, Susan Redmond, Sara Seager, Nicholas Siegler, Karl Stapelfeldt, Sarah Steiger, John Trauger, James Wallace, Marie Ygouf, Neil Zimmerman

JATIS, Vol. 10, Issue 03, 035004, (September 2024) https://doi.org/10.1117/12.10.1117/1.JATIS.10.3.035004

KEYWORDS: Coronagraphy, Planets, Signal to noise ratio, Telescopes, Point spread functions, Stars, Exoplanets, Wavefronts, Spectroscopy, Design

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We summarize the current best polychromatic (∼10% to 20% bandwidth) contrast performance demonstrated in the laboratory by different starlight suppression approaches and systems designed to directly characterize exoplanets around nearby stars. We present results obtained by internal coronagraph and external starshade experimental testbeds using entrance apertures equivalent to off-axis or on-axis telescopes, either monolithic or segmented. For a given angular separation and spectral bandwidth, the performance of each starlight suppression system is characterized by the values of “raw” contrast (before image processing), off-axis (exoplanet) core throughput, and post-calibration contrast (the final 1-sigma detection limit of off-axis point sources, after image processing). Together, the first two parameters set the minimum exposure time required for observations of exoplanets at a given signal-to-noise, i.e., assuming perfect subtraction of background residuals down to the photon noise limit. In practice, residual starlight speckle fluctuations during the exposure will not be perfectly estimated nor subtracted, resulting in a finite post-calibrated contrast and exoplanet detection limit whatever the exposure time. To place the current laboratory results in the perspective of the future Habitable Worlds Observatory (HWO) mission, we simulate visible observations of a fiducial Earth/Sun twin system at 12 pc, assuming a 6 m (inscribed diameter) collecting aperture and a realistic end-to-end optical throughput. The exposure times required for broadband exo-Earth detection (20% bandwidth around λ=0.55 μm) and visible spectroscopic observations (R=70) are then computed assuming various levels of starlight suppression performance, including the values currently demonstrated in the laboratory. Using spectroscopic exposure time as a simple metric, our results point to key starlight suppression system design performance improvements and trades to be conducted in support of HWO’s exoplanet science capabilities. These trades may be explored via numerical studies, lab experiments, and high-contrast space-based observations and demonstrations.

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Proceedings Article | 23 August 2024 Presentation + Paper

The Nancy Grace Roman Space Telescope coronagraph community participation program

Dmitry Savransky, Vanessa Bailey, Schuyler Wolff, Maxwell Millar-Blanchaer, Jason Wang, Lisa Altinier, Ramya Anche, Pierre Baudoz, Beth Biller, Sarah Blunt, Wolfgang Brandner, Marah Brinjikji, Oscar Carrión-González, Amanda Chavez, Elodie Choquet, David Doelman, Julien Girard, Alexandra Greenbaum, Samantha Hasler, Justin Hom, James Ingalls, Stephen Kane, N. Jeremy Kasdin, Oliver Krause, Masayuki Kuzuhara, Alexis Lau, Zhexing Li, John Livingston, Patrick Lowrance, Kevin Ludwick, Bruce Macintosh, Eric Mamajek, Mark Marley, Johan Mazoyer, Bertrand Mennesson, Toshiyuki Mizuki, Sarah Moran, Naoshi Murakami, Jun Nishikawa, Malachi Noel, Laurent Pueyo, Sergi Hildebrandt Rafels, Jason Rhodes, Tyler Robinson, Robert De Rosa, Matthias Samland, Nicholas Schragal, Jürgen Schreiber, Jennifer Sobeck, Karl Stapelfeldt, Motohide Tamura, Taichi Uyajma, Arthur Vigan, Michele Woodland, Marie Ygouf, Kenta Yoneta, Robert Zellem, Neil Zimmerman

Proceedings Volume 13092, 130921I (2024) https://doi.org/10.1117/12.3020514

KEYWORDS: Coronagraphy, Stars, Observatories, Space telescopes, Wavefronts, Telescopes, Planets, Observational astronomy, Exoplanets

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Proceedings Article | 23 August 2024 Paper

The Roman coronagraph community participation program: data reduction and simulations

Maxwell Andrew Millar-Blanchaer, Jason Wang, Ellis Bogat, Jürgen Schreiber, Marie Ygouf, Kevin Ludwick, Alexandra Greenbaum, Vanessa Bailey, Sergi Hildebrandt Rafels, Dmitry Savransky, Matthias Samland, Lisa Altinier, Ramya Anche, Beth Biller, Amanda Chavez, Elodie Choquet, Julien Girard, Justin Hom, James Ingalls, N. Jeremy Kasdin, Oliver Krause, John Livingston, Johan Mazoyer, Laurent Pueyo, Taichi Uyama, Robert Zellem, Neil Zimmerman

Proceedings Volume 13092, 1309256 (2024) https://doi.org/10.1117/12.3020478

KEYWORDS: Calibration, Coronagraphy, Simulations, Observational astronomy, Data processing, Exoplanets, Equipment, Analog electronics, Space telescopes, Signal processing

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Proceedings Article | 5 October 2023 Presentation + Paper

Nancy Grace Roman Space Telescope coronagraph instrument overview and status

Vanessa Bailey, Eduardo Bendek, Brian Monacelli, Caleb Baker, Gasia Bedrosian, Eric Cady, Ewan Douglas, Tyler Groff, Sergi Hildebrandt, N. Jeremy Kasdin, John Krist, Bruce Macintosh, Bertrand Mennesson, Patrick Morrissey, Ilya Poberezhskiy, Hari Subedi, Jason Rhodes, Aki Roberge, Marie Ygouf, Robert Zellem, Feng Zhao, Neil Zimmerman

Proceedings Volume 12680, 126800T (2023) https://doi.org/10.1117/12.2679036

KEYWORDS: Coronagraphy, Equipment, Mirrors, Optical benches, Wavefront sensors, Deformable mirrors, Cameras, Prisms, Observatories, Wavefront errors

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Proceedings Article | 29 August 2022 Poster + Paper

Absolute flux calibrations for the Nancy Grace Roman Space Telescope Coronagraph Instrument

Lindsey Payne, Robert Zellem, Marie Ygouf, Bruce Macintosh

Proceedings Volume 12188, 121884G (2022) https://doi.org/10.1117/12.2628627

KEYWORDS: Stars, Coronagraphy, Calibration, Space telescopes, Planets, Signal to noise ratio, Visibility, Monte Carlo methods, Optical filters, Standards development

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Proceedings Article | 27 August 2022 Poster + Presentation + Paper

JWST/NIRCam coronagraphy: commissioning and first on-sky results

Julien Girard, Jarron Leisenring, Jens Kammerer, Mario Gennaro, Marcia Rieke, John Stansberry, Armin Rest, Eiichi Egami, Ben Sunnquist, Martha Boyer, Alicia Canipe, Matteo Correnti, Bryan Hilbert, Marshall Perrin, Laurent Pueyo, Remi Soummer, Marsha Allen, Howard Bushouse, Jonathan Aguilar, Brian Brooks, Dan Coe, Audrey DiFelice, David Golimowski, George Hartig, Dean Hines, Anton Koekemoer, Bryony Nickson, Nikolay Nikolov, Vera Kozhurina-Platais, Nor Pirzkal, Massimo Robberto, Anand Sivaramakrishnan, Sangmo Tony Sohn, Randal Telfer, Chi Rai Wu, Thomas Beatty, Michael Florian, Kevin Hainline, Doug Kelly, Karl Misselt, Everett Schlawin, Fengwu Sun, Christina Williams, Christopher Willmer, Christopher Stark, Marie Ygouf, Aarynn Carter, Charles Beichman, Thomas Greene, Thomas Roellig, John Krist, Jéa Adams Redai, Jason Wang, Charles Clark, Dan Lewis, Malcolm Ferry

Proceedings Volume 12180, 121803Q (2022) https://doi.org/10.1117/12.2629636

KEYWORDS: Coronagraphy, Stars, James Webb Space Telescope, Point spread functions, Distortion, Telescopes, Signal to noise ratio, Calibration, Target acquisition, Exoplanets, Astronomical imaging, Near infrared, Direct methods, Astronomical instrumentation

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Proceedings Article | 27 August 2022 Presentation + Paper

The Roman Space Telescope coronagraph technology demonstration: current status and relevance to future missions

B. Mennesson, V. Bailey, R. Zellem, S. Hildebrandt, M. Ygouf, J. Rhodes, N. Zimmerman, B. Nemati, G. Gonzalez, E. Cady, B. Kern, T. Koch, J. Krist, K. Heydorff, T. Luchik, F. Mok, P. Morrissey, I. Poberezhskiy, A. Riggs, F. Shi, F. Zhao, R. Akeson, L. Armus, A. Greenbaum, J. Ingalls, P. Lowrance

Proceedings Volume 12180, 121801W (2022) https://doi.org/10.1117/12.2629176

KEYWORDS: Coronagraphy, Wavefront sensors, Electron multiplying charge coupled devices, Imaging spectroscopy, Wavefronts, Stars, Spectroscopy, Performance modeling, Cameras, Observatories

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Proceedings Article | 27 August 2022 Presentation + Paper

Nancy Grace Roman Space Telescope coronagraph instrument observation calibration plan

Robert Zellem, Bijan Nemati, Guillermo Gonzalez, Marie Ygouf, Vanessa Bailey, Eric Cady, M. Mark Colavita, Sergi Hildebrandt, Erin Maier, Bertrand Mennesson, Lindsey Payne, Neil Zimmerman, Ruslan Belikov, Robert De Rosa, John Debes, Ewan Douglas, Julien Girard, Tyler Groff, Jeremy Kasdin, Patrick Lowrance, Bruce Macintosh, Daniel Ryan, Carey Weisberg

Proceedings Volume 12180, 121801Z (2022) https://doi.org/10.1117/12.2627567

KEYWORDS: Calibration, Stars, Coronagraphy, Planets, Sensors, Polarization, Point spread functions, Error analysis, Signal to noise ratio, Uranus

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Proceedings Article | 1 September 2021 Presentation + Paper

The Roman Space Telescope coronagraph technology demonstration: current status and relevance to future missions

B. Mennesson, V. P. Bailey, R. Zellem, N. Zimmerman, M. Ygouf, S. Hildebrandt, J. Rhodes, J. Kasdin, B. Macintosh, M. Turnbull, E. Douglas, A. Mandell, B. Nemati, G. Gonzalez, E. Cady, B. Kern, J. Krist, F. Shi, F. Mok, P. Morrissey, K. Heydorff, I. Pobereszhskiy, F. Zhao, T. Luchik, E. Maier, R. Akeson, L. Armus, J. Ingalls, P. Lowrance, T. Meshkat

Proceedings Volume 11823, 1182310 (2021) https://doi.org/10.1117/12.2603343

KEYWORDS: Coronagraphy, Electron multiplying charge coupled devices, Wavefront sensors, Cameras, Wavefronts, Imaging spectroscopy, Stars, Imaging systems, Spectroscopy, Polarimetry

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Proceedings Article | 23 December 2020 Poster + Paper

Data processing for high-contrast imaging with the James Webb Space Telescope

Marie Ygouf, Graça Rocha, Charles Beichman, Alexandra Greenbaum, Jarron Leisenring, Matthew De Furio, Michael Meyer, Julien Girard, Laurent Pueyo, Marshall Perrin, Taichi Uyama, Joseph Green, Jeffrey Jewell

Proceedings Volume 11443, 114433N (2020) https://doi.org/10.1117/12.2561628

KEYWORDS: James Webb Space Telescope, Data processing, Image processing, Human-computer interaction, Exoplanets, Planets, Point spread functions, Control systems, Coronagraphy, Environmental sensing

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Proceedings Article | 15 December 2020 Presentation + Paper

The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) technology demonstration

N. Jeremy Kasdin, Vanessa Bailey, Bertrand Mennesson, Robert Zellem, Marie Ygouf, Jason Rhodes, Thomas Luchik, Feng Zhao, A. J. Eldorado Riggs, Byoung-Joon Seo, John Krist, Brian Kern, Hong Tang, Bijan Nemati, Tyler Groff, Neil Zimmerman, Bruce Macintosh, Margaret Turnbull, John Debes, Ewan Douglas, Roxana Lupu

Proceedings Volume 11443, 114431U (2020) https://doi.org/10.1117/12.2562997

KEYWORDS: Coronagraphy, Imaging spectroscopy, Planets, Infrared telescopes, James Webb Space Telescope, Imaging systems, Wavefronts, Algorithm development, Jupiter, Infrared radiation

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Proceedings Article | 21 August 2018 Paper

Review of high-contrast imaging systems for current and future ground- and space-based telescopes I: coronagraph design methods and optical performance metrics

G. Ruane, A. Riggs, J. Mazoyer, E. Por, M. N’Diaye, E. Huby, P. Baudoz, R. Galicher, E. Douglas, J. Knight, B. Carlomagno, K. Fogarty, L. Pueyo, N. Zimmerman, O. Absil, M. Beaulieu, E. Cady, A. Carlotti, D. Doelman, O. Guyon, S. Haffert, J. Jewell, N. Jovanovic, C. Keller, M. Kenworthy, J. Kuhn, K. Miller, D. Sirbu, F. Snik, J. Kent Wallace, M. Wilby, M. Ygouf

Proceedings Volume 10698, 106982S (2018) https://doi.org/10.1117/12.2312948

KEYWORDS: Coronagraphy, Space telescopes, Signal to noise ratio, Planets, Point spread functions, Stars, Wavefronts, Telescopes, Optical instrument design, Adaptive optics

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Proceedings Article | 10 July 2018 Presentation + Paper

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes: Part II. Common path wavefront sensing/control and coherent differential imaging

Nemanja Jovanovic, Olivier Absil , Pierre Baudoz, Mathilde Beaulieu, Michael Bottom, Eric Cady, Brunella Carlomagno, Alexis Carlotti, David Doelman, Kevin Fogarty, Raphaël Galicher, Olivier Guyon, Sebastiaan Haffert, Elsa Huby, Jeffrey Jewell, Christoph Keller, Matthew Kenworthy, Justin Knight, Jonas Kühn, Kelsey Miller, Johan Mazoyer, Mamadou N'Diaye, Emiel Por, Laurent Pueyo, A. Riggs, Garreth Ruane, Dan Sirbu, Frans Snik, J. Wallace, Michael Wilby, Marie Ygouf

Proceedings Volume 10703, 107031U (2018) https://doi.org/10.1117/12.2314260

KEYWORDS: Exoplanets, Coronagraphy, Wavefronts, Speckle, Wavefront sensors, Point spread functions, Imaging systems, Cameras, Modulation, Coherence imaging, Phase retrieval

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Proceedings Article | 10 July 2018 Presentation + Paper

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes III: technology opportunities and pathways

Frans Snik, Olivier Absil, Pierre Baudoz, Mathilde Beaulieu, Eduardo Bendek, Eric Cady, Brunella Carlomagno, Alexis Carlotti, Nick Cvetojevic, David Doelman, Kevin Fogarty, Raphaël Galicher, Olivier Guyon, Sebastiaan Haffert, Elsa Huby, Jeffrey Jewell, Nemanja Jovanovic, Christoph Keller, Matthew Kenworthy, Justin Knight, Jonas Kuhn, Johan Mazoyer, Kelsey Miller, Mamadou N'Diaye, Barnaby Norris, Emiel Por, Laurent Pueyo, A. J. Eldorado Riggs, Garreth Ruane, Dan Sirbu, J. Kent Wallace, Michael Wilby, Marie Ygouf

Proceedings Volume 10706, 107062L (2018) https://doi.org/10.1117/12.2313957

KEYWORDS: Coronagraphy, Space telescopes, Imaging systems, Exoplanets, Telescopes, Point spread functions, Liquid crystals, Adaptive optics, Wavefront sensors

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Proceedings Article | 25 September 2017 Open Access

James Webb Space telescope optical simulation testbed: experimental results with linear control alignment

Sylvain Egron, Charles-Philippe Lajoie, Vincent Michau, Aurélie Bonnefois, Clément Escolle, Lucie Leboulleux, Mamadou N'Diaye, Laurent Pueyo, Elodie Choquet, Marshall Perrin, Marie Ygouf, Thierry Fusco, Marc Ferrari, Emmanuel Hugot, Rémi Soummer

Proceedings Volume 10562, 1056225 (2017) https://doi.org/10.1117/12.2296105

KEYWORDS: James Webb Space Telescope, Wavefronts, Space telescopes, Optical alignment, Optical simulations, Mirrors, Optical testing, Telescopes, Wavefront sensors, Astronomical imaging

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Proceedings Article | 29 July 2016 Paper

Data processing and algorithm development for the WFIRST coronagraph: comparison of RDI and ADI strategies and impact of spatial sampling on post-processing

Marie Ygouf, Neil Zimmerman, Laurent Pueyo, Rémi Soummer, Marshall Perrin, Bertrand Mennesson, John Krist, Gautam Vasisht, Bijan Nemati, Bruce Macintosh

Proceedings Volume 9904, 99045M (2016) https://doi.org/10.1117/12.2231581

KEYWORDS: Exoplanets, Point spread functions, Space telescopes, Telescopes, Point spread functions, Stars, Algorithm development, Coronagraphy, Speckle, Planets, Iterated function systems

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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.

Proceedings Article | 29 July 2016 Paper

James Webb Space Telescope optical simulation testbed III: first experimental results with linear-control alignment

Sylvain Egron, Charles-Philippe Lajoie, Lucie Leboulleux, Mamadou N'Diaye, Laurent Pueyo, Élodie Choquet, Marshall Perrin, Marie Ygouf, Vincent Michau, Aurélie Bonnefois, Thierry Fusco, Clément Escolle, Marc Ferrari, Emmanuel Hugot, Rémi Soummer

Proceedings Volume 9904, 99044A (2016) https://doi.org/10.1117/12.2233650

KEYWORDS: James Webb Space Telescope, Wavefront sensors, Space telescopes, Mirrors, Optical simulations, Wavefronts, Telescopes, Optical alignment, Cameras, Zemax

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SPIE Journal Paper | 23 December 2015

Wide-Field Infrared Survey Telescope–Astrophysics Focused Telescope Assets coronagraphic operations: lessons learned from the Hubble Space Telescope and the James Webb Space Telescope

John Debes, Marie Ygouf, Elodie Choquet, Dean Hines, Marshall Perrin, David Golimowski, Charles-Phillipe Lajoie, Johan Mazoyer, Laurent Pueyo, Rémi Soummer, Roeland van der Marel

JATIS, Vol. 2, Issue 01, 011010, (December 2015) https://doi.org/10.1117/12.10.1117/1.JATIS.2.1.011010

KEYWORDS: Coronagraphy, James Webb Space Telescope, Point spread functions, Space telescopes, Telescopes, Infrared telescopes, Stars, Sensors, Space operations, Astronomical telescopes

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Proceedings Article | 16 September 2015 Paper

WFIRST-AFTA coronagraph performance: feedback from post-processing studies to overall design

Bertrand Mennesson, John Krist, Bijan Nemati, Marie Ygouf, Laurent Pueyo, Remi Soummer, Marshall Perrin

Proceedings Volume 9605, 96050D (2015) https://doi.org/10.1117/12.2189403

KEYWORDS: Coronagraphy, Stars, Planets, Point spread functions, Calibration, Wavefronts, Exoplanets, Speckle, Polarization, Image processing

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Proceedings Article | 16 September 2015 Paper

Data processing and algorithm development for the WFIRST-AFTA coronagraph: reduction of noise free simulated images, analysis and spectrum extraction with reference star differential imaging

Marie Ygouf, Laurent Pueyo, Rémi Soummer, Marshall Perrin, Roeland van der Marel, Bruce Macintosh

Proceedings Volume 9605, 96050S (2015) https://doi.org/10.1117/12.2188669

KEYWORDS: Point spread functions, Planets, Coronagraphy, Image processing, Data modeling, Monochromatic aberrations, Stars, Exoplanets, Iterated function systems, Computer simulations

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Proceedings Article | 2 August 2014 Paper

James Webb Space Telescope Optical Simulation Testbed I: overview and first results

Marshall Perrin, Rémi Soummer, Élodie Choquet, Mamadou N'Diaye, Olivier Levecq, Charles-Philippe Lajoie, Marie Ygouf, Lucie Leboulleux, Sylvain Egron, Rachel Anderson, Chris Long, Erin Elliott, George Hartig, Laurent Pueyo, Roeland van der Marel, Matt Mountain

Proceedings Volume 9143, 914309 (2014) https://doi.org/10.1117/12.2056936

KEYWORDS: James Webb Space Telescope, Mirrors, Image segmentation, Wavefront sensors, Telescopes, Phase retrieval, Adaptive optics, Optical alignment, Space telescopes, Sensors

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Proceedings Article | 19 September 2007 Paper

A new concept of achromatic phase shifter for nulling interferometry

Daniel Rouan, D. Pelat, Marie Ygouf, Jean-Michel Reess, Fanny Chemla, Pierre Riaud

Proceedings Volume 6693, 669316 (2007) https://doi.org/10.1117/12.725855

KEYWORDS: Mirrors, Phase shifts, Planets, Stars, Nulling interferometry, Telescopes, Interferometers, Photons, Manufacturing, Signal to noise ratio

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Direct detection and characterization of a planet around a star by nulling interferometry, must be efficient in a large wavelength domain in order to detect simultaneously the infrared bio-tracers CO₂, O₃ and H₂O. This condition requires that an achromatic phase shift of π be implemented, with an accuracy sufficient for achieving a deep nulling at all considered wavelengths. Several solutions have been presented. We present here a new concept for designing such an achromatic phase shifter. It is based on two cellular mirrors (alternatively, transparent plates can be used) where cells have thickness which are respectively odd and even multiples of a quarter of the central wavelength. Each cell introduces then a phase shift of (2k + 1)π or of 2kπ, on the fraction of the wave it reflects. Each mirror is introduced in the collimated beam issued from one or the other telescopes. Because of the odd/even distribution, a destructive interference is obviously produced on axis for the central wavelength when recombining the two beams. The trick to obtain a quasi-achromatisation is to distribute the thickness of the cells, so that the nulling is also efficient for a wavelength not too far from the central wavelength. We show that if the thicknesses are distributed according to the Pascal triangle, a fair quasi-achromatism is reached. This effect is the more efficient that the number of cells is large. For instance, with 256 × 256 cells, where phase shift range is between -6π and +6π one shows that the nulling reaches 10^-6 on the wavelength range [0.7λ₀, 1.3λ₀] which corresponds roughly to the DARWIN specification. In a second step, we study the optimum way to distribute the cells in the plane of the pupil. The most important criterion is the isolation of the planet image from the residual image of the star. Several efficient configurations are presented. Finally we consider some practical aspects on a device belonging to the real world and on the bench we are developing. The major interest of this solution is that it allows a compact, simple and fully symmetric design, with essentially no ajustable sub-systems ; extension to multi-telescopes interferometers with phase shift other than π can also be envisioned.

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