22,544 research outputs found
SAOLIM, a prototype of a low cost System for Adaptive Optics with Lucky Imaging
A prototype of a low cost Adaptive Optics (AO) system has been developed at
the Instituto de Astrofisica de Andalucia (CSIC) and tested at the 2.2m
telescope of the Calar Alto observatory. We present here the status of the
project, which includes the image stabilization system and compensation of high
order wavefront aberrations with a membrane deformable mirror. The image
stabilization system consists of magnet driven tip-tilt mirror. The higher
order compensation system comprises of a Shack-Hartmann sensor, a membrane
deformable mirror with 39 actuators and the control computer that allows
operations up to 420Hz in closed loop mode. We have successfully closed the
high order AO loop on natural guide stars. An improvement of 4 times in terms
of FWHM was achieved. The description and the results obtained on the sky are
presented in this paper.Comment: Accepted for publishing in PASP, 11 pages, 14 figures, 6 table
The Infrared Imaging Spectrograph (IRIS) for TMT: Data Reduction System
IRIS (InfraRed Imaging Spectrograph) is the diffraction-limited first light
instrument for the Thirty Meter Telescope (TMT) that consists of a
near-infrared (0.84 to 2.4 m) imager and integral field spectrograph
(IFS). The IFS makes use of a lenslet array and slicer for spatial sampling,
which will be able to operate in 100's of different modes, including a
combination of four plate scales from 4 milliarcseconds (mas) to 50 mas with a
large range of filters and gratings. The imager will have a field of view of
3434 arcsec with a plate scale of 4 mas with many selectable
filters. We present the preliminary design of the data reduction system (DRS)
for IRIS that need to address all of these observing modes. Reduction of IRIS
data will have unique challenges since it will provide real-time reduction and
analysis of the imaging and spectroscopic data during observational sequences,
as well as advanced post-processing algorithms. The DRS will support three
basic modes of operation of IRIS; reducing data from the imager, the lenslet
IFS, and slicer IFS. The DRS will be written in Python, making use of
open-source astronomical packages available. In addition to real-time data
reduction, the DRS will utilize real-time visualization tools, providing
astronomers with up-to-date evaluation of the target acquisition and data
quality. The quicklook suite will include visualization tools for 1D, 2D, and
3D raw and reduced images. We discuss the overall requirements of the DRS and
visualization tools, as well as necessary calibration data to achieve optimal
data quality in order to exploit science cases across all cosmic distance
scales.Comment: 13 pages, 2 figures, 6 tables, Proceeding 9913-165 of the SPIE
Astronomical Telescopes + Instrumentation 201
Linear-Array Photoacoustic Imaging Using Minimum Variance-Based Delay Multiply and Sum Adaptive Beamforming Algorithm
In Photoacoustic imaging (PA), Delay-and-Sum (DAS) beamformer is a common
beamforming algorithm having a simple implementation. However, it results in a
poor resolution and high sidelobes. To address these challenges, a new
algorithm namely Delay-Multiply-and-Sum (DMAS) was introduced having lower
sidelobes compared to DAS. To improve the resolution of DMAS, a novel
beamformer is introduced using Minimum Variance (MV) adaptive beamforming
combined with DMAS, so-called Minimum Variance-Based DMAS (MVB-DMAS). It is
shown that expanding the DMAS equation results in multiple terms representing a
DAS algebra. It is proposed to use the MV adaptive beamformer instead of the
existing DAS. MVB-DMAS is evaluated numerically and experimentally. In
particular, at the depth of 45 mm MVB-DMAS results in about 31 dB, 18 dB and 8
dB sidelobes reduction compared to DAS, MV and DMAS, respectively. The
quantitative results of the simulations show that MVB-DMAS leads to improvement
in full-width-half-maximum about 96 %, 94 % and 45 % and signal-to-noise ratio
about 89 %, 15 % and 35 % compared to DAS, DMAS, MV, respectively. In
particular, at the depth of 33 mm of the experimental images, MVB-DMAS results
in about 20 dB sidelobes reduction in comparison with other beamformers.Comment: This is the final version of this paper, which is accepted in the
"Journal of Biomedical Optics". Compared to previous versions, this version
contains more experiments and evaluatio
Generalized Inpainting Method for Hyperspectral Image Acquisition
A recently designed hyperspectral imaging device enables multiplexed
acquisition of an entire data volume in a single snapshot thanks to
monolithically-integrated spectral filters. Such an agile imaging technique
comes at the cost of a reduced spatial resolution and the need for a
demosaicing procedure on its interleaved data. In this work, we address both
issues and propose an approach inspired by recent developments in compressed
sensing and analysis sparse models. We formulate our superresolution and
demosaicing task as a 3-D generalized inpainting problem. Interestingly, the
target spatial resolution can be adjusted for mitigating the compression level
of our sensing. The reconstruction procedure uses a fast greedy method called
Pseudo-inverse IHT. We also show on simulations that a random arrangement of
the spectral filters on the sensor is preferable to regular mosaic layout as it
improves the quality of the reconstruction. The efficiency of our technique is
demonstrated through numerical experiments on both synthetic and real data as
acquired by the snapshot imager.Comment: Keywords: Hyperspectral, inpainting, iterative hard thresholding,
sparse models, CMOS, Fabry-P\'ero
Single conjugate adaptive optics for the ELT instrument METIS
The ELT is a 39m large, ground-based optical and near- to mid-infrared
telescope under construction in the Chilean Atacama desert. Operation is
planned to start around the middle of the next decade. All first light
instruments will come with wavefront sensing devices that allow control of the
ELT's intrinsic M4 and M5 wavefront correction units, thus building an adaptive
optics (AO) system. To take advantage of the ELT's optical performance, full
diffraction-limited operation is required and only a high performance AO system
can deliver this. Further technically challenging requirements for the AO come
from the exoplanet research field, where the task to resolve the very small
angular separations between host star and planet, has also to take into account
the high-contrast ratio between the two objects. We present in detail the
results of our simulations and their impact on high-contrast imaging in order
to find the optimal wavefront sensing device for the METIS instrument. METIS is
the mid-infrared imager and spectrograph for the ELT with specialised
high-contrast, coronagraphic imaging capabilities, whose performance strongly
depends on the AO residual wavefront errors. We examined the sky and target
sample coverage of a generic wavefront sensor in two spectral regimes, visible
and near-infrared, to pre-select the spectral range for the more detailed
wavefront sensor type analysis. We find that the near-infrared regime is the
most suitable for METIS. We then analysed the performance of Shack-Hartmann and
pyramid wavefront sensors under realistic conditions at the ELT, did a
balancing with our scientific requirements, and concluded that a pyramid
wavefront sensor is the best choice for METIS. For this choice we additionally
examined the impact of non-common path aberrations, of vibrations, and the
long-term stability of the SCAO system including high-contrast imaging
performance.Comment: 37 pages, 27 figures, accepted for publication in Experimental
Astronom
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