45 research outputs found
Ingot Laser Guide Stars Wavefront Sensing
We revisit one class of z-invariant WaveFront sensor where the LGS is fired
aside of the telescope aperture. In this way there is a spatial dependence on
the focal plane with respect to the height where the resonant scattering
occurs. We revise the basic parameters involving the geometry and we propose
various merit functions to define how much improvement can be attained by a
z-invariant approach. We show that refractive approaches are not viable and we
discuss several solutions involving reflective ones in what has been nicknamed
"ingot wavefront sensor" discussing the degrees of freedom required to keep
tracking and the basic recipe for the optical design.Comment: 6 pages, 4 figures, AO4ELT5 Conference Proceeding, 201
A Holographic Diffuser Generalised Optical Differentiation Wavefront Sensor
The wavefront sensors used today at the biggest World's telescopes have
either a high dynamic range or a high sensitivity, and they are subject to a
linear trade off between these two parameters. A new class of wavefront
sensors, the Generalised Optical Differentiation Wavefront Sensors, has been
devised, in a way not to undergo this linear trade off and to decouple the
dynamic range from the sensitivity. This new class of WFSs is based on the
light filtering in the focal plane from a dedicated amplitude filter, which is
a hybrid between a linear filter, whose physical dimension is related to the
dynamic range, and a step in the amplitude, whose size is related to the
sensitivity. We propose here a possible technical implementation of this kind
of WFS, making use of a simple holographic diffuser to diffract part of the
light in a ring shape around the pin of a pyramid wavefront sensor. In this
way, the undiffracted light reaches the pin of the pyramid, contributing to the
high sensitivity regime of the WFS, while the diffused light is giving a sort
of static modulation of the pyramid, allowing to have some signal even in high
turbulence conditions. The holographic diffuser zeroth order efficiency is
strictly related to the sensitivity of the WFS, while the diffusing angle of
the diffracted light gives the amount of modulation and thus the dynamic range.
By properly choosing these two parameters it is possible to build a WFS with
high sensitivity and high dynamic range in a static fashion. Introducing
dynamic parts in the setup allows to have a set of different diffuser that can
be alternated in front of the pyramid, if the change in the seeing conditions
requires it.Comment: 11 pages, 5 figure
Multiple spatial frequencies wavefront sensing
We describe the concept of splitting spatial frequency perturbations into
some kind of pupil planes wavefront sensors. Further to the existing approach
of dropping higher spatial frequency to suppress aliasing effects (the
so-called spatial filtered Shack-Hartmann), we point out that spatial
frequencies splitting and mixing of these in a proper manner, could be handled
in order to exhibit some practical or fundamental advantages. In this framework
we describe the idea behind such class of concepts and we derive the
relationship useful to determine if, by which extent, and under what kind of
merit function, these devices can overperform existing conventional sensors.Comment: 6 pages, 3 figures, in AO4ELT5 Proceeding
Prospects of Deep Field Surveys with Global-MCAO on an ELT
Several astronomical surveys aimed at the investigation of the extragalactic
components were carried out in order to map systematically the universe and its
constituents. An excellent level of detail is needed, and it is possible only
using space telescopes or with the application of adaptive optics (AO)
techniques for ground-based observatories. By simulating K-band observations of
6000 high-redshift galaxies in the Chandra Deep Field South region, we have
already shown how an extremely large telescope can carry out photometric
surveys successfully using the Global-MCAO, a natural guide stars based
technique that allows the development of extragalactic research, otherwise
impracticable without using laser guide stars. As the outcome of the analysis
represents an impact science case for the new instruments on upcoming
ground-based telescopes, here we show how the investigation of other observed
deep fields could profit from such a technique. Further to an overview of the
surveys suitable for the proposed approach, we show preliminary estimations
both on geometrical (FoV and height) and purely AO perspectives (richness and
homogeneity of guide stars in the area) for planned giant telescope.Comment: 8 pages, 6 figures, AO4ELT5 conferenc
SHARK-NIR, the coronagraphic camera for LBT, moving toward construction
SHARK-NIR is one of the two coronagraphic instruments proposed for the Large
Binocular Telescope. Together with SHARK-VIS (performing coronagraphic imaging
in the visible domain), it will offer the possibility to do binocular
observations combining direct imaging, coronagraphic imaging and coronagraphic
low resolution spectroscopy in a wide wavelength domain, going from 0.5{\mu}m
to 1.7{\mu}m. Additionally, the contemporary usage of LMIRCam, the
coronagraphic LBTI NIR camera, working from K to L band, will extend even more
the covered wavelength range. In January 2017 SHARK-NIR underwent a successful
final design review, which endorsed the instrument for construction and future
implementation at LBT. We report here the final design of the instrument, which
foresees two intermediate pupil planes and three focal planes to accomodate a
certain number of coronagraphic techniques, selected to maximize the instrument
contrast at various distances from the star. Exo-Planets search and
characterization has been the science case driving the instrument design, but
the SOUL upgrade of the LBT AO will increase the instrument performance in the
faint end regime, allowing to do galactic (jets and disks) and extra-galactic
(AGN and QSO) science on a relatively wide sample of targets, normally not
reachable in other similar facilities.Comment: 8 pages, 6 figures, AO4ELT5 conference proceeding
MAVIS: The adaptive optics module feasibility study
The Adaptive Optics Module of MAVIS is a self-contained MCAO module, which delivers a corrected FoV to the postfocal scientific instruments, in the visible. The module aims to exploit the full potential of the ESO VLT UT4 Adaptive Optics Facility, which is composed of the high spatial frequency deformable secondary mirror and the laser guide stars launching and control systems. During the MAVIS Phase A, we evaluated, with the support of simulations and analysis at different levels, the main terms of the error budgets aiming at estimating the realistic AOM performance. After introducing the current opto-mechanical design and AO scheme of the AOM, we here present the standard wavefront error budget and the other budgets, including manufacturing, alignment of the module, thermal behavior and noncommon path aberrations, together with the contribution of the upstream telescope system
SHARK-NIR: from K-band to a key instrument, a status update
SHARK-NIR channel is one of the two coronagraphic instruments proposed for the Large Binocular Telescope, in the framework of the call for second generation instruments, issued in 2014. Together with the SHARK-VIS channel, it will offer a few observing modes (direct imaging, coronagraphic imaging and coronagraphic low resolution spectroscopy) covering a wide wavelength domain, going from 0.5ÎĽm to 1.7ÎĽm. Initially proposed as an instrument covering also the K-band, the current design foresees a camera working from Y to H bands, exploiting in this way the synergy with other LBT instruments such as LBTI, which is actually covering wavelengths greater than L' band, and it will be soon upgraded to work also in K band. SHARK-NIR has been undergoing the conceptual design review at the end of 2015 and it has been approved to proceed to the final design phase, receiving the green light for successive construction and installation at LBT. The current design is significantly more flexible than the previous one, having an additional intermediate pupil plane that will allow the usage of coronagraphic techniques very efficient in term of contrast and vicinity to the star, increasing the instrument coronagraphic performance. The latter is necessary to properly exploit the search of giant exo-planets, which is the main science case and the driver for the technical choices of SHARK-NIR. We also emphasize that the LBT AO SOUL upgrade will further improve the AO performance, making possible to extend the exo-planet search to target fainter than normally achieved by other 8-m class telescopes, and opening in this way to other very interesting scientific scenarios, such as the characterization of AGN and Quasars (normally too faint to be observed) and increasing considerably the sample of disks and jets to be studied. Finally, we emphasize that SHARK-NIR will offer XAO direct imaging capability on a FoV of about 15"x15", and a simple coronagraphic spectroscopic mode offering spectral resolution ranging from few hundreds to few thousands. This article presents the current instrument design, together with the milestones for its installation at LBT. <P /