121 research outputs found
Shaped pupil design for the Gemini Planet Imager
The Gemini Planet Imager (GPI) is an instrument designed for the Gemini South
telescope to image young Jupiter-mass planets in the infrared. To achieve the
high contrast needed for this, it employs an apodized pupil Lyot coronagraph
(APLC) to remove most of the starlight. Current designs use a
partially-transmitting apodizer in the pupil; we examine the use of binary
apodizations in the form of starshaped shaped pupils, and present a design that
could achieve comparable performance, along with a series of design guidelines
for creating shaped pupil versions of APLCs in other systems.Comment: 20 pages, 7 figures, accepted for publication in Ap
High Performance Lyot and PIAA Coronagraphy for Arbitrarily shaped Telescope Apertures
Two high performance coronagraphic approaches compatible with segmented and
obstructed telescope pupils are described. Both concepts use entrance pupil
amplitude apodization and a combined phase and amplitude focal plane mask to
achieve full coronagraphic extinction of an on-axis point source. While the
first concept, named Apodized Pupil Complex Mask Lyot Coronagraph (APCMLC),
relies on a transmission mask to perform the pupil apodization, the second
concept, named Phase-Induced Amplitude Apodization complex mask coronagraph
(PIAACMC), uses beam remapping for lossless apodization. Both concepts
theoretically offer complete coronagraphic extinction (infinite contrast) of a
point source in monochromatic light, with high throughput and sub-lambda/D
inner working angle, regardless of aperture shape. The PIAACMC offers nearly
100% throughput and approaches the fundamental coronagraph performance limit
imposed by first principles. The steps toward designing the coronagraphs for
arbitrary apertures are described for monochromatic light. Designs for the
APCMLC and the higher performance PIAACMC are shown for several monolith and
segmented apertures, such as the apertures of the Subaru Telescope, Giant
Magellan Telescope (GMT), Thirty Meter Telescope (TMT), the European Extremely
Large Telescope (E-ELT) and the Large Binocular Telescope (LBT). Performance in
broadband light is also quantified, suggesting that the monochromatic designs
are suitable for use in up to 20% wide spectral bands for ground-based
telescopes.Comment: 19 pages, 12 figures, accepted for publication in Ap
Optimal Occulter Design for Finding Extrasolar Planets
One proposed method for finding terrestrial planets around nearby stars is to
use two spacecraft--a telescope and a specially shaped occulter that is
specifically designed to prevent all but a tiny fraction of the starlight from
diffracting into the telescope. As the cost and observing cadence for such a
mission will be driven largely by the separation between the two spacecraft, it
is critically important to design an occulter that can meet the observing goals
while flying as close to the telescope as possible. In this paper, we explore
this tradeoff between separation and occulter diameter. More specifically, we
present a method for designing the shape of the outer edge of an occulter that
is as small as possible and gives a shadow that is deep enough and large enough
for a 4m telescope to survey the habitable zones of many stars for Earth-like
planets. In particular, we show that in order for a 4m telescope to detect in
broadband visible light a planet 0.06 arcseconds from a star shining
times brighter than the planet requires a specially-shaped occulter 50m in
diameter positioned about km in front of the telescope.Comment: 14 pages, 4 figures, 15 subfigure
A dual-mask coronagraph for observing faint companions to binary stars
Observations of binary stars for faint companions with conventional
coronagraphic methods are challenging, as both targets will be bright enough to
obscure any nearby faint companions if their scattered light is not suppressed.
We propose coronagraphic examination of binary stars using an apodized pupil
Lyot coronagraph and a pair of actively-controlled image plane masks to
suppress both stars simultaneously. The performance is compared to imaging with
a band-limited mask, a dual-mask Lyot coronagraph and with no coronagraph at
all. An imaging procedure and control system for the masks are also described.Comment: 17 pages, 6 figure
Boundary diffraction wave integrals for diffraction modeling of external occulters
An occulter is a large diffracting screen which may be flown in conjunction
with a telescope to image extrasolar planets. The edge is shaped to minimize
the diffracted light in a region beyond the occulter, and a telescope may be
placed in this dark shadow to view an extrasolar system with the starlight
removed. Errors in position, orientation, and shape of the occulter will
diffract additional light into this region, and a challenge of modeling an
occulter system is to accurately and quickly model these effects. We present a
fast method for the calculation of electric fields following an occulter, based
on the concept of the boundary diffraction wave: the 2D structure of the
occulter is reduced to a 1D edge integral which directly incorporates the
occulter shape, and which can be easily adjusted to include changes in occulter
position and shape, as well as the effects of sources---such as
exoplanets---which arrive off-axis to the occulter. The structure of a typical
implementation of the algorithm is included.Comment: 13 pages, 5 figure
REVIEWED COMMENTARY: FACTORY-GROWN WOOD, THE FUTURE OF FORESTRY?
Recent developments in factory-grown foods suggest that factory-grown wood (FGW) may be on the horizon. In fact, recent work at Massachusetts Institute of Technology introduces tunable plant-based materials, an early indicator of what may evolve into a new source of raw material for forest sector companies, and others. Industry and academia would be wise to monitor developments in this field as they may present significant opportunities and/or adjustments for both. We explore the state-of-the-art in this budding area of science and contemplate implications of successfully growing wood or other lignocellulosic materials in factories. Given a changing climate and focus on carbon emissions, the pressure to drastically reduce CO2 production will continue climb. Could reduction of their footprint via FGW be an important part of this equation for forest sector companies, going beyond the need to “make every tree count”? In other words, might FGW present an environmental and climate protection breakthrough? Or might it simply trade forest-based environmental impacts for others? What other consequences does FGW promise for companies? And, what might it mean for wood science programs, critical suppliers of research & development and skilled employees for the industry? We explore each of these questions and contemplate potential actions and outcomes.
Real-time speckle sensing and suppression with project 1640 at Palomar
Palomar’s Project 1640 (P1640) is the first stellar coronagraph to regularly use active coronagraphic wavefront control (CWFC). For this it has a hierarchy of offset wavefront sensors (WFS), the most important of which is the higher-order WFS (called CAL), which tracks quasi-static modes between 2-35 cycles-per-aperture. The wavefront is measured in the coronagraph at 0.01 Hz rates, providing slope targets to the upstream Palm 3000 adaptive optics (AO) system. The CWFC handles all non-common path distortions up to the coronagraphic focal plane mask, but does not sense second order modes between the WFSs and the science integral field unit (IFU); these modes determine the system’s current limit. We have two CWFC operating modes: (1) P-mode, where we only control phases, generating double-sided darkholes by correcting to the largest controllable spatial frequencies, and (2) E-mode, where we can control amplitudes and phases, generating single-sided dark-holes in specified regions-of-interest. We describe the performance and limitations of both these modes, and discuss the improvements we are considering going forward
Commissioning and performance results of the WFIRST/PISCES integral field spectrograph
The Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies
(PISCES) is a high contrast integral field spectrograph (IFS) whose design was
driven by WFIRST coronagraph instrument requirements. We present commissioning
and operational results using PISCES as a camera on the High Contrast Imaging
Testbed at JPL. PISCES has demonstrated ability to achieve high contrast
spectral retrieval with flight-like data reduction and analysis techniques.Comment: Author's copy - Proceedings of SPIE Volume 10400. Citation to SPIE
proceedings volume will be added when availabl
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