20,051 research outputs found
Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses.
AIM: To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses. METHODS: Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device (LAMBDA-X, Belgium). Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance (far, intermediate, and near) and pupil size was also analyzed. RESULTS: The power distribution of the lenses was affected by pupil size differently. One of the lenses showed a significant spread in refractive power distribution, from about -3 D to 0 D. Generally, the power distribution of the lenses expanded as the pupil diameter became greater. The surface of the lens dedicated for each distance varied substantially with the design of the lens. CONCLUSION: In an experimental basis, our results show how the lenses power distribution is affected by the pupil size and underlined the necessity of careful evaluation of the patient's visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome
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
Exoplanets imaging with a Phase-Induced Amplitude Apodization Coronagraph - I. Principle
Using 2 aspheric mirrors, it is possible to apodize a telescope beam without
losing light or angular resolution: the output beam is produced by
``remapping'' the entrance beam to produce the desired light intensity
distribution in a new pupil. We present the Phase-Induced Amplitude Apodization
Coronagraph (PIAAC) concept, which uses this technique, and we show that it
allows efficient direct imaging of extrasolar terrestrial planets with a
small-size telescope in space. The suitability of the PIAAC for exoplanet
imaging is due to a unique combination of achromaticity, small inner working
angle (about 1.5 ), high throughput, high angular resolution and
large field of view. 3D geometrical raytracing is used to investigate the
off-axis aberrations of PIAAC configurations, and show that a field of view of
more than 100 in radius is available thanks to the correcting
optics of the PIAAC. Angular diameter of the star and tip-tilt errors can be
compensated for by slightly increasing the size of the occulting mask in the
focal plane, with minimal impact on the system performance. Earth-size planets
at 10 pc can be detected in less than 30s with a 4m telescope. Wavefront
quality requirements are similar to classical techniques.Comment: 35 pages, 16 figures, Accepted for publication in Ap
Double stage Lyot coronagraph with the apodized reticulated stop for extremely large telescope
One of the science drivers for the extremely large telescope (ELT) is imaging
and spectroscopy of exo-solar planets located as close as 20mas to their parent
star. The application requires a well thought-out design of the high contrast
imaging instrumentation. Several working coronagraphic concepts have already
been developed for the monolithic telescope with the diameter up to 8 meter.
Nevertheless the conclusions made about the performance of these systems cannot
be applied directly to the telescope of the diameter 30-100m. The existing
schemes are needed to be reconsidered taking into account the specific
characteristics of a segmented surface. We start this work with the classical
system ? Lyot coronagraph. We show that while the increase in telescope
diameter is an advantage for the high contrast range science, the segmentation
sets a limit on the performance of the coronagraph. Diffraction from
intersegment gaps sets a floor to the achievable extinction of the starlight.
Masking out the bright segment gaps in the Lyot plane although helps increasing
the contrast, does not solve completely the problem: the high spatial frequency
component of the diffractive light remains. We suggest using the Lyot stop
which acts on the light within gaps in order to produce the uniform
illumination in the Lyot plane. We show that for the diffraction limit regime
and a perfect phasing this type of coronagraph achieves a sufficient star light
extinction.Comment: 11 pages, 12 figures, SPIE conference 5905, 200
Band-Limited Coronagraphs using a halftone-dot process: II. Advances and laboratory results for arbitrary telescope apertures
The band-limited coronagraph is a nearly ideal concept that theoretically
enables perfect cancellation of all the light of an on-axis source. Over the
past years, several prototypes have been developed and tested in the
laboratory, and more emphasis is now on developing optimal technologies that
can efficiently deliver the expected high-contrast levels of such a concept.
Following the development of an early near-IR demonstrator, we present and
discuss the results of a second-generation prototype using halftone-dot
technology. We report improvement in the accuracy of the control of the local
transmission of the manufactured prototype, which was measured to be less than
1%.
This advanced H-band band-limited device demonstrated excellent contrast
levels in the laboratory, down to 10-6 at farther angular separations than 3
lambda/D over 24% spectral bandwidth. These performances outperform the ones of
our former prototype by more than an order of magnitude and confirm the
maturity of the manufacturing process.
Current and next generation high-contrast instruments can directly benefit
from such capabilities. In this context, we experimentally examine the ability
of the band-limited coronagraph to withstand various complex telescope
apertures.Comment: Accepted in ApJ - under pres
Ground-Based Coronagraphy with High Order Adaptive Optics
We summarize the theory of coronagraphic optics, and identify a dimensionless
fine-tuning parameter, F, which we use to describe the Lyot stop size in the
natural units of the coronagraphic optical train and the observing wavelength.
We then present simulations of coronagraphs matched to adaptive optics (AO)
systems on the Calypso 1.2m, Palomar Hale 5m and Gemini 8m telescopes under
various atmospheric conditions, and identify useful parameter ranges for AO
coronagraphy on these telescopes. Our simulations employ a tapered, high-pass
filter in spatial frequency space to mimic the action of adaptive wavefront
correction. We test the validity of this representation of AO correction by
comparing our simulations with recent K-band data from the 241-channel Palomar
Hale AO system and its dedicated PHARO science camera in coronagraphic mode.Comment: To appear in ApJ, May 2001 (28 pages, 10 figs
Shaped Pupil Lyot Coronagraphs: High-Contrast Solutions for Restricted Focal Planes
Coronagraphs of the apodized pupil and shaped pupil varieties use the
Fraunhofer diffraction properties of amplitude masks to create regions of high
contrast in the vicinity of a target star. Here we present a hybrid coronagraph
architecture in which a binary, hard-edged shaped pupil mask replaces the gray,
smooth apodizer of the apodized pupil Lyot coronagraph (APLC). For any contrast
and bandwidth goal in this configuration, as long as the prescribed region of
contrast is restricted to a finite area in the image, a shaped pupil is the
apodizer with the highest transmission. We relate the starlight cancellation
mechanism to that of the conventional APLC. We introduce a new class of
solutions in which the amplitude profile of the Lyot stop, instead of being
fixed as a padded replica of the telescope aperture, is jointly optimized with
the apodizer. Finally, we describe shaped pupil Lyot coronagraph (SPLC) designs
for the baseline architecture of the Wide-Field Infrared Survey
Telescope-Astrophysics Focused Telescope Assets (WFIRST-AFTA) coronagraph.
These SPLCs help to enable two scientific objectives of the WFIRST-AFTA
mission: (1) broadband spectroscopy to characterize exoplanet atmospheres in
reflected starlight and (2) debris disk imaging.Comment: 41 pages, 15 figures; published in the JATIS special section on
WFIRST-AFTA coronagraph
Focused and defocused retinal images with Bessel and axicon pupil functions.
Retinal image light distributions in a standard optical model of a diffraction-limited eye with round pupils are presented for several patterns of amplitude and phase modulation of the light admitted into the eye. Of special interest are circularly symmetrical configurations of truncated Bessel amplitude transmission functions, and of light subjected to axicon deviation. It is shown by several examples that this kind of beam shaping allows generation of retinal imagery, which can be more robust to defocus while maintaining minimal image degradation, and it points to situations of two separate zones simultaneously in sharp focus, several diopters apart
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