Laser Guide Star for 3.6m and 8m telescopes: Performances and astrophysical implications

We have constructed an analytical model to simulate the behavior of an adaptive optics system coupled with a sodium laser guide star. The code is applied to a 3.6-m and 8m class telescopes. The results are given in terms of Strehl ratio and full width at half maximum of the point spread function. Two atmospheric models are used, one representing good atmospheric conditions (20 per cent of the time), the other median conditions. Sky coverage is computed for natural guide star and laser guide star systems, with two different methods. The first one is a statistical approach, using stellar densities, to compute the probability to find a nearby reference. The second is a cross-correlation of a science object catalogue and the USNO catalogue. Results are given in terms of percentage of the sky that can be accessed with given performances, and in terms of number of science object that can be observed, with Strehls greater than 0.2 and 0.1 in K and J bands.Comment: 14 pages, 17 figures, accepted for publication in MNRAS. Also available at: http://www-obs.univ-lyon1.fr/~lelouarn

The High-Superior-Tension Technique: Evolution of Lipoabdominoplasty

Because abdominoplasty is associated with complications such as seroma and necrosis as well as epigastric bulging and a suprapubic scar located too high, the demand for this procedure is not as high as it otherwise might be. However, although these negative effects were common many years ago, their incidence has decreased dramatically with modern abdominoplastic techniques. One approach using a combination of abdominoplasty and liposuction or lipoabdominoplasty has resolved many of the problems faced with earlier techniques, offering aesthetically pleasing results and excellent reliability. The keys to successful lipoabdominoplasty, first developed as the high-superior-tension technique, are extensive liposuction, preservation of lymphatic trunks, preaponeurotic epigastric dissection, major muscle fascia plication, two high-tension paraumbilical sutures, hypogastric tension sutures, and closure of the dead spaces. The most recent updates to this technique are described in this article

Validation Through Simulations of a Cn2 Profiler for the ESO/VLT Adaptive Optics Facility

The Adaptive Optics Facility (AOF) project envisages transforming one of the VLT units into an adaptive telescope and providing its ESO (European Southern Observatory) second generation instruments with turbulence corrected wavefronts. For MUSE and HAWK-I this correction will be achieved through the GALACSI and GRAAL AO modules working in conjunction with a 1170 actuators Deformable Secondary Mirror (DSM) and the new Laser Guide Star Facility (4LGSF). Multiple wavefront sensors will enable GLAO and LTAO capabilities, whose performance can greatly benefit from a knowledge about the stratification of the turbulence in the atmosphere. This work, totally based on end-to-end simulations, describes the validation tests conducted on a Cn2 profiler adapted for the AOF specifications. Because an absolute profile calibration is strongly dependent on a reliable knowledge of turbulence parameters r0 and L0, the tests presented here refer only to normalized output profiles. Uncertainties in the input parameters inherent to the code are tested as well as the profiler response to different turbulence distributions. It adopts a correction for the unseen turbulence, critical for the GRAAL mode, and highlights the effects of masking out parts of the corrected wavefront on the results. Simulations of data with typical turbulence profiles from Paranal were input to the profiler, showing that it is possible to identify reliably the input features for all the AOF modes.Comment: 15 pages, 12 figures, accepted for publication in the MNRAS Accepted 2015 January 22. Received 2015 January 21; in original form 2014 December

Simulations of Adaptive Optics Systems for the E-ELT

ABSTRACT In this paper, we present simulation work done on AO systems for the E-ELT. We study the influence of the number of Laser Guide Stars (LGS) on system performance. Then, we investigate the impact of the conjugation height of the M4 adaptive mirror on GL/LT/MC-AO. Finally, we compare the results of a Fourier code and end-to-end models on the position of the LGS in the field of view

Prism matching for piston segmentation correction with adaptive optics systems on extremely large telescopes

Images observed at ground-based telescopes are blurred by Earth’s atmosphere. Adaptive optics systems can correct for this blurring by using a wavefront sensor to measure the instantaneous wavefront aberration created by the atmosphere, and a deformable mirror to apply correction to the aberrated wavefront. The European Extremely Large Telescope, one of the next generation of telescopes currently under construction, will have large supporting struts or arms (spiders) for the secondary mirror that obscure whole rows and columns of subapertures in the wavefront sensor. This phase discontinuity can allow large segment piston errors to arise between neighbouring segments, because the deformable mirror can produce the segment modes but the wavefront sensor senses them poorly. The spider for the EELT will have six arms, and we propose in this paper employing a six-sided prism for the wavefront sensor instead of the traditional four sided pyramid. We show that when the diffraction spikes from the spider arms are aligned in the middle of the prism faces, the sensitivty of the sensor, as measured by the sum of the singular values of the interaction matrix for the six segment piston modes, is 15% larger than if the diffraction spikes are aligned with the prism edges

Modeling of pulsed laser guide stars for the Thirty Meter Telescope project

The Thirty Meter Telescope (TMT) has been designed to include an adaptive optics system and associated laser guide star (LGS) facility to correct for the image distortion due to Earth's atmospheric turbulence and achieve diffraction-limited imaging. We have calculated the response of mesospheric sodium atoms to a pulsed laser that has been proposed for use in the LGS facility, including modeling of the atomic physics, the light-atom interactions, and the effect of the geomagnetic field and atomic collisions. This particular pulsed laser format is shown to provide comparable photon return to a continuous-wave (cw) laser of the same average power; both the cw and pulsed lasers have the potential to satisfy the TMT design requirements for photon return flux.Comment: 16 pages, 20 figure

Characterizing the Adaptive Optics Off-Axis Point-Spread Function - I: A Semi-Empirical Method for Use in Natural-Guide-Star Observations

Even though the technology of adaptive optics (AO) is rapidly maturing, calibration of the resulting images remains a major challenge. The AO point-spread function (PSF) changes quickly both in time and position on the sky. In a typical observation the star used for guiding will be separated from the scientific target by 10" to 30". This is sufficient separation to render images of the guide star by themselves nearly useless in characterizing the PSF at the off-axis target position. A semi-empirical technique is described that improves the determination of the AO off-axis PSF. The method uses calibration images of dense star fields to determine the change in PSF with field position. It then uses this information to correct contemporaneous images of the guide star to produce a PSF that is more accurate for both the target position and the time of a scientific observation. We report on tests of the method using natural-guide-star AO systems on the Canada-France-Hawaii Telescope and Lick Observatory Shane Telescope, augmented by simple atmospheric computer simulations. At 25" off-axis, predicting the PSF full width at half maximum using only information about the guide star results in an error of 60%. Using an image of a dense star field lowers this error to 33%, and our method, which also folds in information about the on-axis PSF, further decreases the error to 19%.Comment: 29 pages, 9 figures, accepted for publication in the PAS