120 research outputs found
Review of high-contrast imaging systems for current and future ground-based and space-based telescopes III: technology opportunities and pathways
The Optimal Optical CoronagraphWorkshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 30 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. This contribution is the final part of a series of three papers summarizing the outcomes of the workshop, and presents an overview of novel optical technologies and systems that are implemented or considered for high-contrast imaging instruments on both ground-based and space telescopes. The overall objective of high contrast instruments is to provide direct observations and characterizations of exoplanets at contrast levels as extreme as 10^(-10). We list shortcomings of current technologies, and identify opportunities and development paths for new technologies that enable quantum leaps in performance. Specifically, we discuss the design and manufacturing of key components like advanced deformable mirrors and coronagraphic optics, and their amalgamation in "adaptive coronagraph" systems. Moreover, we discuss highly integrated system designs that combine contrast-enhancing techniques and characterization techniques (like high-resolution spectroscopy) while minimizing the overall complexity. Finally, we explore extreme implementations using all-photonics solutions for ground-based telescopes and dedicated huge apertures for space telescopes
Preliminary design of the full-Stokes UV and visible spectropolarimeter for UVMag/Arago
The UVMag consortium proposed the space mission project Arago to ESA at its
M4 call. It is dedicated to the study of the dynamic 3D environment of stars
and planets. This space mission will be equipped with a high-resolution
spectropolarimeter working from 119 to 888 nm. A preliminary optical design of
the whole instrument has been prepared and is presented here. The design
consists of the telescope, the instrument itself, and the focusing optics.
Considering not only the scientific requirements, but also the cost and size
constraints to fit a M-size mission, the telescope has a 1.3 m diameter primary
mirror and is a classical Cassegrain-type telescope that allows a
polarization-free focus. The polarimeter is placed at this Cassegrain focus.
This is the key element of the mission and the most challenging to be designed.
The main challenge lies in the huge spectral range offered by the instrument;
the polarimeter has to deliver the full Stokes vector with a high precision
from the FUV (119 nm) to the NIR (888 nm). The polarimeter module is then
followed by a high-resolution echelle-spectrometer achieving a resolution of
35000 in the visible range and 25000 in the UV. The two channels are separated
after the echelle grating, allowing a specific cross-dispersion and focusing
optics for the UV and visible ranges. Considering the large field of view and
the high numerical aperture, the focusing optic for both the UV and visible
channels is a Three-Mirror-Anastigmat (TMA) telescope, in order to focus the
various wavelengths and many orders onto the detectors.Comment: 6 pages, 6 figures, IAUS 30
UVMag: Space UV and visible spectropolarimetry
UVMag is a project of a space mission equipped with a high-resolution
spectropolarimeter working in the UV and visible range. This M-size mission
will be proposed to ESA at its M4 call. The main goal of UVMag is to measure
the magnetic fields, winds and environment of all types of stars to reach a
better understanding of stellar formation and evolution and of the impact of
stellar environment on the surrounding planets. The groundbreaking combination
of UV and visible spectropolarimetric observations will allow the scientists to
study the stellar surface and its environment simultaneously. The instrumental
challenge for this mission is to design a high-resolution space
spectropolarimeter measuring the full-Stokes vector of the observed star in a
huge spectral domain from 117 nm to 870 nm. This spectral range is the main
difficulty because of the dispersion of the optical elements and of
birefringence issues in the FUV. As the instrument will be launched into space,
the polarimetric module has to be robust and therefore use if possible only
static elements. This article presents the different design possibilities for
the polarimeter at this point of the project.Comment: 9 pages, 4 figures, SPIE Conference Astronomical Telescopes +
Instrumentation Montreal June 201
Pupil Plane Phase Apodization
Phase apodization coronagraphs are implemented in a pupil plane to create a
dark hole in the science camera focal plane. They are successfully created as
"Apodizing Phase Plates" (APPs) using classical optical manufacturing, and as
"vector-APPs" using liquid-crystal patterning with essentially achromatic
performance. This type of coronagraph currently delivers excellent broadband
contrast (10) at small angular separations (few ) at
ground-based telescopes, owing to their insensitivity to tip/tilt errors.Comment: Invited chapter, to be published in the "Handbook of Astronomical
Instrumentation", Vol. 3, eds. A. Moore and D. Burrows, WSPC (2018). 9 pages,
1 figur
The Vector-APP: a Broadband Apodizing Phase Plate that yields Complementary PSFs
The apodizing phase plate (APP) is a solid-state pupil optic that clears out
a D-shaped area next to the core of the ensuing PSF. To make the APP more
efficient for high-contrast imaging, its bandwidth should be as large as
possible, and the location of the D-shaped area should be easily swapped to the
other side of the PSF. We present the design of a broadband APP that yields two
PSFs that have the opposite sides cleared out. Both properties are enabled by a
half-wave liquid crystal layer, for which the local fast axis orientation over
the pupil is forced to follow the required phase structure. For each of the two
circular polarization states, the required phase apodization is thus obtained,
and, moreover, the PSFs after a quarter-wave plate and a polarizing
beam-splitter are complementary due to the antisymmetric nature of the phase
apodization. The device can be achromatized in the same way as half-wave plates
of the Pancharatnam type or by layering self-aligning twisted liquid crystals
to form a monolithic film called a multi-twist retarder. As the VAPP introduces
a known phase diversity between the two PSFs, they may be used directly for
wavefront sensing. By applying an additional quarter-wave plate in front, the
device also acts as a regular polarizing beam-splitter, which therefore
furnishes high-contrast polarimetric imaging. If the PSF core is not saturated,
the polarimetric dual-beam correction can also be applied to polarized
circumstellar structure. The prototype results show the viability of the
vector-APP concept.Comment: Proc. SPIE 8450-2
The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environments
The raw coronagraphic performance of current high-contrast imaging
instruments is limited by the presence of a quasi-static speckle (QSS)
background, resulting from instrumental non-common path errors (NCPEs). Rapid
development of efficient speckle subtraction techniques in data reduction has
enabled final contrasts of up to 10-6 to be obtained, however it remains
preferable to eliminate the underlying NCPEs at the source. In this work we
introduce the coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront
sensor suitable for real-time NCPE correction. This pupil-plane optic combines
the apodizing phase plate coronagraph with a holographic modal wavefront
sensor, to provide simultaneous coronagraphic imaging and focal-plane wavefront
sensing using the science point spread function. We first characterise the
baseline performance of the cMWS via idealised closed-loop simulations, showing
that the sensor successfully recovers diffraction-limited coronagraph
performance over an effective dynamic range of +/-2.5 radians root-mean-square
(RMS) wavefront error within 2-10 iterations. We then present the results of
initial on-sky testing at the William Herschel Telescope, and demonstrate that
the sensor is able to retrieve injected wavefront aberrations to an accuracy of
10nm RMS under realistic seeing conditions. We also find that the cMWS is
capable of real-time broadband measurement of atmospheric wavefront variance at
a cadence of 50Hz across an uncorrected telescope sub-aperture. When combined
with a suitable closed-loop adaptive optics system, the cMWS holds the
potential to deliver an improvement in raw contrast of up to two orders of
magnitude over the uncorrected QSS floor. Such a sensor would be eminently
suitable for the direct imaging and spectroscopy of exoplanets with both
existing and future instruments, including EPICS and METIS for the E-ELT.Comment: 14 pages, 12 figures: accepted for publication in Astronomy &
Astrophysic
Polarization Modeling and Predictions for DKIST Part 2: Application of the Berreman Calculus to Spectral Polarization Fringes of Beamsplitters and Crystal Retarders
We outline polarization fringe predictions derived from a new application of
the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder
optics. The DKIST retarder baseline design used 6 crystals, single-layer
anti-reflection coatings, thick cover windows and oil between all optical
interfaces. This new tool estimates polarization fringes and optic Mueller
matrices as functions of all optical design choices. The amplitude and period
of polarized fringes under design changes, manufacturing errors, tolerances and
several physical factors can now be estimated. This tool compares well with
observations of fringes for data collected with the SPINOR spectropolarimeter
at the Dunn Solar Telescope using bi-crystalline achromatic retarders as well
as laboratory tests. With this new tool, we show impacts of design decisions on
polarization fringes as impacted by anti-reflection coatings, oil refractive
indices, cover window presence and part thicknesses. This tool helped DKIST
decide to remove retarder cover windows and also recommends reconsideration of
coating strategies for DKIST. We anticipate this tool to be essential in
designing future retarders for mitigation of polarization and intensity fringe
errors in other high spectral resolution astronomical systems.Comment: Accepted for publication in JATI
M&m's: An error budget and performance simulator code for polarimetric systems
Although different approaches to model a polarimeter's accuracy have been
described before, a complete error budgeting tool for polarimetric systems has
not been yet developed. Based on the framework introduced by Keller & Snik, in
2009, we have developed the M&m's code as a first attempt to obtain a generic
tool to model the performance and accuracy of a given polarimeter, including
all the potential error contributions and their dependencies on physical
parameters. The main goal of the code is to provide insight on the combined
influence of many polarization errors on the accuracy of any polarimetric
instrument. In this work we present the mathematics and physics based on which
the code is developed as well as its general structure and operational scheme.
Discussion of the advantages of the M&m's approach to error budgeting and
polarimetric performance simulation is carried out and a brief outlook of
further development of the code is also given.Comment: Publ. date: 09/201
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