MICADO, the Multi-AO-Imaging-Camera and Spectrometer for Deep Observations, is one of the first light instruments for the future 40 m class Extremely Large Telescope (ELT). MICADO utilizes the advanced laser guide star multiconjugate adaptive optics system MCAO developed by the MAORY consortium and the jointly developed singleconjugate adaptive optics system (SCAO). We present an overview on the conceptual design of the MICADO Cold Optical Instrument (COI) which comprises the infrared focal plane imager with its 3 x 3 4k2 HgCdTe detector array and a compact cross-dispersing slit spectrometer operating in the spectral range of 0.8 to 2.4 μm. High contrast imaging is enabled via a classical configuration of coronagraph and Lyot stops. The paper summarizes the MICADO COI interchangeable optics, its cryogenic implementation together with the modular opto-mechanical configuration of the cryo-mechanisms and the cryo-vacuum cooling system, which consists of a continuous LN2 flow cryostat.
By adding a dedicated coronagraph, ESO in collaboration with the Breakthrough Initiatives, modifies the Very Large Telescope mid-IR imager (VISIR) to further boost the high dynamic range imaging capability this instru- ment has. After the VISIR upgrade in 2012, where coronagraphic masks were first added to VISIR, it became evident that coronagraphy at a ground-based 8m-class telescope critically needs adaptive optics, even at wavelengths as long as 10μm. For VISIR, a work-horse observatory facility instrument in normal operations, this is ”easiest” achieved by bringing VISIR as a visiting instrument to the ESO-VLT-UT4 having an adaptive M2. This “visit” enables a meaningful search for Earth-like planets in the habitable zone around both α-Cen1,2. Meaningful here means, achieving a contrast of ≈ 10-6 within ≈ 0.8arcsec from the star while maintaining basically the normal sensitivity of VISIR. This should allow to detect a planet twice the diameter of Earth. Key components will be a diffractive coronagraphic mask, the annular groove phase mask (AGPM), optimized for the most sensitive spectral band-pass in the N-band, complemented by a sophisticated apodizer at the level of the Lyot stop. For VISIR noise filtering based on fast chopping is required. A novel internal chopper system will be integrated into the cryostat. This chopper is based on the standard technique from early radio astronomy, conceived by the microwave pioneer Robert Dicke in 1946, which was instrumental for the discovery of the 3K radio background.
The commissioning of the telescope and its first instrument, a Nasmyth port mounted 0.5 degree CCD mosaic imager, started in November 2013. We will report about the results of astronomical tests of the integrated system including the achieved optical quality across the field of view, pointing and tracking quality and operational experiences with the observatory system. The special design features of this alt-az telescope are its compactness and the low-ghost wide field optics (0.7o f.o.v. diameter), and we will briefly report on the lessons learned especially for these special features. We will present an outlook on the further commissioning including the additional instruments which are all under construction or already finalized.
LUCI (former LUCIFER) is the full cryogenic near-infrared multi-object spectrograph and imager at the LBT. It presently allows for seeing limited imaging and multi-object spectroscopy at R~2000-4000 in a 4x4arcmin2 FOV from 0.9 to 2.5 micron. We report on the instrument performance and the lessons learned during the first two years on sky from a technical and operational point of view. We present the upcoming detector upgrade to Hawaii-2 RG arrays and the operating modes to utilize the binocular mode, the LBT facility AO system for diffraction limited imaging as well as to use the wide-field AO correction afforded by the multi-laser GLAO System ARGOS in multi-object spectroscopy.
Due to the exposed location of the Wendelstein observatory on the steep summit of mount Wendelstein no road exists to
transport telescope components and heavy equipment to the observatory in order to install the new 2m Fraunhofer
Telescope Wendelstein (FTW) in its new dome. A two step installation concept was therefore followed to mitigate any
risks that essential hardware would not work once installed on the mountain.
This paper reports on the telescope factory assembly and tests, including on-sky tests, which were performed in early
summer 2011 at the factory site to make sure, that the telescope and all essential subsystems are working properly before
the telescope would be installed on the mountain. The telescope was disassembled again to be transported to the
mountain in summer. Lifting of all structural subsystems and the optics up to the mountain observatory with the help of a
heavy lift helicopter will be presented in detail, also looking at specific design drivers, logistic aspects and special tools
for installation of the telescope and its mirrors in its new dome. Handling and transport concept for the M1 mirror
installation, which also will have to be used when the mirror is disassembled for recoating, are presented. Up to end of
2011 the telescope installation and pre-alignment could be completed including first on-sky tests. The system will
undergo a detailed performance test campaign in the first halve of 2012. Current performance results of these
commissioning activities will be reported.
The integration of the 2m Fraunhofer telescope started in August 2011 at the Mt. Wendelstein observatory. The
logistics of the project are a key problem of the integration as the observatory has no road access. All large
or heavy components inlcuding the primary mirror were successfully delivered by helicopter. Meanwhile, they
are integrated in the telescope. The special design features of this alt-az telescope are its compactness and the
low-ghost wide field optics (0.7 deg. f.o.v. diameter).
We will briefly report on tests of the building and of the telescope system before the telescope moved to the
mountain. The integration at the observatory and the first astronomical performances tests of the telescopes are
discussed, and a brief update on the status of its instruments is presented. We comment on the cleaning and
recoating strategy for the primary mirror based on sample tests.
LUCIFER1 is a NIR camera and spectrograph installed at the Large Binocular Telescope (LBT). Working in
the wavelength range of 0.9-2.5micron, the instrument is designed for direct imaging and spectroscopy with 3
different cameras. A set of longslit masks as well as up to 23 user defined (MOS) masks are available. The set
of user defined masks can be exchanged while the instrument is at operating temperature.
Extensive tests have been done on the electro-mechanical functions, image motion due to flexure, optical
quality, instrument software, calibration and especially on the multi-object spectroscopy. Also a detailed characterization
of the instrument's properties in the different observing modes has been carried out. Results are
presented and compared to the specifications.
ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field
adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding
wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial
beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above
each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to
ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical
distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field
correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial
resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its
ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.
The LUCIFER-MOS unit is the full cryogenic mask-exchange unit for the near-infrared multi-object spectrograph
LUCIFER at the Large Binocular Telescope. We present the design and functionality of this unique device. In LUCIFER
the masks are stored, handled, and placed in the focal plane under cryogenic conditions at all times, resulting in very low
thermal background emission from the masks during observations. All mask manipulations are done by a novel
cryogenic mask handling robot that can individually address up to 33 fixed and user-provided masks and place them in
the focal plane with high accuracy. A complete mask exchange cycle is done in less than five minutes and can be run in
every instrument position and state reducing instrument setup time during science observations to a minimum. Exchange
of old and new MOS masks is likewise done under cryogenic conditions using a unique exchange drive mechanism and
two auxiliary cryostats that attach to the main instrument cryostat.
The successful roll-out of the control software for a complex NIR imager/spectrograph with MOS calls for
flexible development strategies due to changing requirements during different phases of the project. A waterfall
strategy used in the beginning has to change to a more iterative and agile process in the later stages. The
choice of an appropriate program language as well as suitable software layout is crucial. For example the
software has to accomplish multiple demands of different user groups, including a high level of flexibility for
later changes and extensions. Different access levels to the instrument are mandatory to afford direct control
mechanisms for lab operations and inspections of the instrument as well as tools to accomplish efficient science
observations. Our hierarchical software structure with four layers of increasing abstract levels and the use of an
object oriented language ideally supports these requirements. Here we describe our software architecture, the
software development process, the different access levels and our commissioning experiences with LUCIFER 1.
MICADO is the adaptive optics imaging camera for the E-ELT. It has been designed and optimised to be mounted
to the LGS-MCAO system MAORY, and will provide diffraction limited imaging over a wide (~1 arcmin) field
of view. For initial operations, it can also be used with its own simpler AO module that provides on-axis
diffraction limited performance using natural guide stars. We discuss the instrument's key capabilities and
expected performance, and show how the science drivers have shaped its design. We outline the technical
concept, from the opto-mechanical design to operations and data processing. We describe the AO module,
summarise the instrument performance, and indicate some possible future developments.
LUCIFER 1 is the rst of two identical camera-spectrograph units installed at the LBT (Large Binocular Telescope)
on Mount Graham in Arizona. Its commissioning took place between September 2008 and November
2009 and has immediately been followed by science operations since December 2009.
LUCIFER has a 4x4 arcminute eld of view. It is equipped with a 2048x2048 pixel HAWAII-2 array, suitable
lters (broad-band z, J, H, K & Ks plus 12 medium and narrow band near-infrared lters) and three gratings for
spectroscopy for a resolution of up to 15000. LUCIFER has 3 cameras: two specic for seeing limited imaging
(the N3.75 camera, with 0.12"/pixel) and spectroscopy (the N1.8 camera, with 0.25"/pixel) and one for diraction
limited observations (the N30 camera). We report here about the completed seeing-limited commissioning, thus
using only two of the cameras.
We have developed an PSF reconstruction algorithm for the NAOS adaptive optics system that is coupled with CONICA at ESO/VLT. We have modified the algorithm of Véran et al. (1997), originally written for PUEO at CFHT, to make use of the specific real-time wavefront-related data that observers with NACO receive together with their scientific images. In addition, we use the Vii algorithm introduced by Clénet et al. (2006) and Gendron et al. (2006) instead of the Uij algorithm originally used by Véran et al. (1997).
Until now, tests on NAOS has been undertaken during technical time thanks to the NACO team at Paranal. A first test has been successfully performed to calibrate the orientation of reconstructed PSFs with respect to NACO images. We have also obtained two sets of PSF reconstruction test data with NACO in November 2006 and September 2007 to reconstruct PSFs. Discrepancies exist between the observed and reconstructed PSFs: their Strehl ratios are ~31% and ~39% respectively in Nov. 2006, ~31% and ~19% respectively in Sept. 2007. These differences may be at least partly explained by reconstructions that either did not account for the aliasing contribution or poorly estimated the noise contribution with the available noise information at that time.
We have additionally just started to test our algorithm using the AO bench Sésame, at LESIA. Results are promising but need to be extended to a larger set of atmospheric conditions or AO correction qualities.
LUCIFER is a NIR spectrograph and imager (wavelength range 0.9 to 2.5 micron) for the Large Binocular
Telescope (LBT) on Mt. Graham, Arizona, working at cryogenic temperatures of less than 70K. Two instruments
are built by a consortium of five German institutes and will be mounted at the bent Gregorian foci of the two
individual telescope mirrors. Three exchangable cameras are available for imaging and spectroscopy: two of
them are optimized for seeing-limited conditions, a third camera for the diffraction limited case will be used with
the LBT adaptive secondary mirror working. Up to 33 exchangeable masks are available for longslit or multi-object
spectroscopy (MOS) over the full field of view (FOV). Both MOS-units (LUCIFER 1 and LUCIFER
2) and the auxiliary cryostats together with the control electronics have been completed. The observational
software-package is in its final stage of preparation.
After the total integration of LUCIFER 1 extensive tests were done for all electro-mechanical functions and
the verification of the instrument started. The results of the tests are presented in detail and are compared with
HAWK-I is the newly commissioned High Acuity Wide-field K-band Imager at the ESO Very Large Telescope. It is a
0.9-2.5 micron imager with a field of view of 7.5×7.5 arcmin sampled at 106 mas with four Hawaii2RG detectors. It has
a full reflective design that was optimised for image quality and throughput.We present an overview of its performance as
measured during the commissioning and first science runs. In particular, we describe a detector read-out mode that allows
us to increase the useful dynamic range of the detector, and a distortion calibration resulting in <5mas relative astrometry
across the field.
Laser guide star adaptive optics and interferometry are currently revolutionizing ground-based near-IR astronomy, as
demonstrated at various large telescopes. The Large Binocular Telescope from the beginning included adaptive optics in
the telescope design. With the deformable secondary mirrors and a suite of instruments taking advantage of the AO
capabilities, the LBT will play an important role in addressing major scientific questions. Extending from a natural guide
star based system, towards a laser guide stars will multiply the number of targets that can be observed. In this paper we
present the laser guide star and wavefront sensor program as currently being planned for the LBT. This program will
provide a multi Rayleigh guide star constellation for wide field ground layer correction taking advantage of the multi
object spectrograph and imager LUCIFER in a first step. The already foreseen upgrade path will deliver an on axis
diffraction limited mode with LGS AO based on tomography or additional sodium guide stars to even further enhance
the scientific use of the LBT including the interferometric capabilities.
Adaptive optics (AO) allows one to derive the point spread function (PSF) simultaneously to the science image,
which is a major advantage in post-processing tasks such as astrometry/photometry or deconvolution. Based on
the algorithm of Veran et al. (1997), PSF reconstruction has been developed for four different AO systems so far:
PUEO, ALFA, Lick-AO and Altair. A similar effort is undertaken for NAOS/VLT in a collaboration between
the group PHASE (Onera and Observatoire de Paris/LESIA) and ESO. In this paper, we first introduce two
new algorithms that prevent the use of the so-called "Uij functions" to: (1) avoid the storage of a large amount
of data (for both new algorithms), (2) shorten the PSF reconstruction computation time (for one of the two)
and (3) provide an estimation of the PSF variability (for the other one). We then identify and explain issues in
the exploitation of real-time Shack-Hartmann (SH) data for PSF reconstruction, emphasising the large impact
of thresholding in the accuracy of the phase residual estimation. Finally, we present the data provided by the
NAOS real-time computer (RTC) to reconstruct PSF ((1) the data presently available, (2) two NAOS software
modifications that would provide new data to increase the accuracy of the PSF reconstruction and (3) the tests
of these modifications) and the PSF reconstruction algorithms we are developing for NAOS on that basis.
NACO is a VLT/Yepun instrument which provides adaptive optics corrected images in the near and thermal infrared. It is composed of the NAOS adaptive optics system and of an infrared imager CONICA. NACO has been operating since October 2001 and has already delivered a large amount of scientific results in various fields, eg the Solar System (Titan), the Interstellar Medium (outflows in Orion-OMC1), the Galactic Center, the central regions of AGN and ULIRG, ... We present the instrument performance in terms of image quality after two years of operation at Paranal. We first remind the system performance obtained from simulations, design, tests and compare them to the original specifications. We point out the telescope vibrations as a source of performance degradation. We then evaluate the impact of these vibrations on the Strehl ratio. We eventually analyze studies of the telescope vibrations to identify the systems that could excite the telescope vibration modes.
An on-line estimation of turbulence parameters (r0, L0 and wind speed) and Adaptive Optics (AO) performance using NAOS [Nasmyth Adaptive Optics System] is presented. The method is based on the reconstruction of open-loop data from deformable mirror voltages and residual wavefront sensor slopes obtained in closed loop. This dedicated tool implemented in the real time computer of the NAOS system (first AO of the Very Large Telescope) allows without any loop opening to automatically monitor and display (every 15 seconds) both the atmospheric conditions and the system performance. We have validated the algorithm and tested its robustness on simulated and experimental data (both in laboratory and on sky). Using data obtained during more than two years of operations, statistical study on NAOS performance and turbulence characteristics are proposed. An on-line estimation of turbulence parameters (r0, L0 and wind speed)
and Adaptive Optics (AO) performance is presented.
In preparation for upcoming sodium laser guide star for adaptive optics, a spectroscopic study of the amount of sodium, present in the Earth atmosphere, has been undertaken. Preliminary results of almost 3 years of monitoring are presented here.
In October 2002 the VLT Adaptive Optics (AO) facility instrument NAOS-CONICA (NACO) was offered for the first time to the astronomical community and has been operated successfully ever since. NACO is capable of performing AO assisted imaging, spectroscopy, polarimetry, and coronography. One exciting and unique observing capability of NACO is its cold tunable Fabry-Perot Interferometer, that will be offered in October 2004. The 3-dimensional structure analysis of extended objects, such as planetary nebulae, is one interesting application of this device that combines imaging and medium resolution spectroscopy in the K-band. Using VLT day and night time commissioning data, the performance of the Fabry-Perot is evaluated and a strategy to handle the complex calibration and data reduction has been developed.
The Nasmyth Adaptive Optics System (NAOS) and the High-Resolution Near
IR Camera (CONICA) are mounted at the Nasmyth B focus of Yepun (UT4)
telescope of the ESO VLT. NACO (NAOS+CONICA) is an IR (1-5 micron)
imager, spectrograph, coronograph and polarimeter which is fed by the
NAOS - the first adaptive optics system installed on Paranal. NACO
data products are pipeline-processed, and quality checked, by the Data
Flow Operations Group in Garching. The calibration data are processed
to create calibration products and to extract Quality Control (QC)
parameters. These parameters provide health checks and monitor
instrument's performance. They are stored in a database, compared to
earlier data, trended over time and made available on the NACO QC web
page that is updated daily.
NACO is an evolving instrument where new observing modes are offered
with every observing period. Naturally, the list of QC parameters that
are monitored evolves as well. We present current QC parameters of
NACO and discuss the general process of controlling data
quality and monitoring instrument performance.
We present and discuss the capabilities of the infrared polarimetric modes of the ESO-VLT adaptive optics system NAOS-CONICA. Commissioning results obtained both with wire-grids and Wollaston prisms are shown. In particular, NACO observations of the Calabash
reflection nebula are compared with earlier, seeing limited, results
obtained at ESO to illustrate the new potential offered by adaptive
optics assisted polarimetry on an 8m class telescope.
The Homunculus nebula, surrounding the massive star system Η Carinae, is a bipolar dust nebula which is outflowing at up to 700 km/s. The bipolar lobes display high linear polarization in the optical and near-IR, which is consistent with an origin in dust scattering from the central source. Extensive imaging and spectropolarimetric studies have not however been able to provide a consistent picture of the dust which has been ejected in the mass loss events, the most important of which occurred in the 1840's. The magnitude of the linear polarization shows very little change with wavelength, suggesting very small grains. On the other hand, models of the IR emission suggest a mixed grain population. The scattering
properties of feasible dust mixtures do not however well match the
observed optical and near-infrared polarization behaviour. Three possibilities are advanced to explain the dust grain population in the Homunculus: optical depth effects within a clumped distribution; the presence of many small clouds with grain size dependent on depth into the cloud; large-scale grain alignment. The last suggestion is supported by observation of 10μ polarization. Visible light circular polarization observations and refined geometric dust-scattering models are presented to advance the picture of the dust in the Homunculus. Since the dust ejected from Η Carinae is several solar masses, this study is also relevant to the understanding of ISM dust.
The realtime knowledge of the altitude and optical characteristics of a generated Laser Guide Star may be necessary for an independent control of the performances of the associated adaptive optics system. For this ourpose a robotic laser guide star monitoring facility, based on a small telescope physically separated from the observatory has been studied, as a subsystem of the VLT LGS project. After reviewing the state of the art on sodium layer dynamical characteristics, we describe the rationale of the project and the main technical choices. Some particular aspects such as differential field motion and laser plume centroiding algorithms are reviewed in detail. The data processing architecture and the associated pipeline is described, and the expected performances are estimated.
We describe the current status of the ELP-OA project in which we try to demonstrate in practice that it is possible to measure the tilt of a wave front using only a polychromatic laser guide star and no natural guide star. The first phase of ELP-OA, consisting of feasibility experiments, has recently been completed successfully. This paper provides an overview over the results of this first phase and over the continuation of the ELP-OA project.
Adaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS.
This paper summarizes three years of observations of the resonant optical backscatter of laser, used to produce a mesospheric sodium-layer laser guide star for an adaptive optics system. Observations were obtained from a neighboring telescope. The aim of this work was two-fold: to study the Na plume (altitude and profile variations) and to study the Rayleigh cone in order to achieve scattering measurements relevant to the light pollution created by a sodium laser guide star. We report on the short-term characteristics of the sodium layer and stress the consequences of these variations for Laser Guide Star Adaptive Optics System operations. From the measurements of the background intensity measured while observing the laser guide star and the top of the Rayleigh cone, we can derive information on the light pollution produced by the laser as well as the resulting implications for an observatory laser management policy. Information on the laser intensity, size and shape along the Rayleigh cone are also presented.
Adaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source, which is located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength of the observation, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. Several papers have addressed the problem of the sky coverage as a function of these parameters (see e.g.: Le Louarn et al). It turns out that the sky coverage is disastrously low in particular in the short (visible) wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (which is not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return- of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because approximately equals 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial or total sky coverage for the tilt, such as the dual adaptive optics concept, the elongation perspective method, or the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play.
We present results from measurements of the return flux from a polychromatic sodium laser guide star produced in Pierrelatte, France during the PASS-2 experiment. In the experiment, photometry of light at 330, 569, 589, and 589.6 nm emitted by mesospheric sodium under two-color laser excitation (569 and 589 nm) was performed. The variation of oscillator and laser configurations as well as simultaneous measurements of the atmospheric coherence length and the mesospheric sodium density permit a comparison of the results with atomic physics models. Using the results, we can determine the setup that produces the maximum return flux from the polychromatic laser guide star. The knowledge gained will be used to aid the ELP- OA project, which has as its goal the design, testing, and implementation of an adaptive optics system that uses a polychromatic laser guide star for wave front tilt measurements.
Observations have shown the presence of sodium layer centroid height variations of a few hundred meters on timescales of tens of seconds. As quality laser guide star (LGS) plus adaptive optics (AO) assisted astronomy, especially on large (8m+) telescopes, will require optimal scheduling of observations and regular laser and wavefront sensor focusing at sites where sporadic sodium layers are frequent, an 'easy to use' sodium layer monitor is required. LIDAR offers a convenient means to achieve this. By pulsing the outgoing sodium laser and performing time-of-flight measurements on the returned photons we can acquire the altitude profile of the sodium layer. Unfortunately, conventional LIDAR requires the laser duty cycle to be very low, therefore large integration times are required. However, by using a cross-correlation technique the duty cycle can be increased to 50%, which gives far better performance. We present the details of this technique which involved amplitude modulation of the MPIA/MPE ALFA cw laser, as well as the following results of such LIDAR measurements performed in October 1999 at the 3.5 m telescope at Calar Alto Observatory in Spain. The altitude of the sodium layer at Calar Alto on 17th and 18th October 1999 was found to be at 90 +/- 3 km and there is evidence for sporadics on one of two nights with sporadic layer FWHM* varying from approximately 240 to 350 m. In addition, a noticeable layer FWHM change (excluding the sporadic layer) from approximately 13 to approximately 5 - 7 km was observed over the two nights. After flux and altitude calibration and correction of the projected altitude range, a very good agreement is found between sodium layer profiles derived from an auxiliary telescope and 3.5 m telescope LIDAR observations. Using an intensity weighted centroid algorithm the centroid height of the sodium layer was observed to have a variation of < 500 m in approximately 10 minutes. Although, shorter timescale variations may be have been present, poor observing conditions and resulting reduced S/N prevents this analysis.
The optical backscatter of the 4W CW laser used to produce a mesospheric sodium-layer laser guide star for the MPE adaptive optics system (ALFA) has been observed from a neighboring 2.2 m telescope. The observations, taken at the Max Planck Observatory in Calar-Alto (Spain), in August 1998, had two aims: study the Na plume (altitude and profile variations) and the Rayleigh cone to achieve Rayleigh scattering measurements. In the framework of the network, `Laser Guide Star for 8 m class telescopes', a program of the European Commission, ESO, MPE and NUI, Galway are collaborating on studying the light pollution due to the MPE ALFA laser.
This paper describes the effects of Laser Guide Star spot elongation and Rayleigh scattering on wavefront sensing performances. An analytical model of Rayleigh scattering and a numerical model of laser plume generation at the altitude of the atmospheric sodium layer were developed. These models, integrated into a general Adaptive Optics (AO) simulation, provide information about the non-uniform centroid measurement accuracy on the sensor sub-apertures. The effects of laser power, laser type, laser launching position, sensor sampling and sensor field of view on the AO loop performances are analyzed and discussed.
High angular resolution adaptive optics data have been obtained on (eta) Carinae and Homunculus nebula, with the ESO ADONIS system. In the broad band filters, J, H and K, the central source, (eta) Car was allowed to saturate in order to maximize the signal for the extended Homunculus nebula. Unsaturated images were also obtained in a narrow continuum filter. The purpose of these observations was to explore the 3D shape of the Homunculus through high spatial resolution imaging polarimetry. The polarization of resolved knots and filaments, will allow their position along the line of sight to be determined when combined with scattering models. Here the observational details, data reduction and preliminary results are presented.
Post processing of data obtained from the European Southern Observatory's ADONIS system is presented here. A physically constrained iterative deconvolution algorithm is applied to two distinctly different objects demonstrating both object and point spread function recovery. Surface features are found in thermal imaging of Io which compare well with Galileo measurements of vulcanism. Anisoplanatic behavior of the ADONIS system is studied with wide field imaging of the cluster NGC1850.
Post processing of data obtained from the European Southern Observatory’s ADONIS system is presented here. A physically constrained iterative deconvolution algorithm is applied to both bright and faint object data demonstrating both object and point spread function recovery. Comparisons are made with standard linear and non-linear deconvolution algorithms. Simulated data is used to investigate the combined system and post-processing performance on faint extended objects.