Characterization of the sodium layer at Cerro Pachón, and impact on laser guide star performance

Neichel, Benoît; d’Orgeville, Céline; Callingham, J. R.; Rigaut, François; Winge, Cláudia; Trancho, Gelys

doi:10.1093/mnras/sts631

Cited by 28 publications

(25 citation statements)

References 19 publications

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“…• Better understanding of the laser coupling efficiency to sodium [45] and of the sodium layer [46][47] will continue to be developed.…”

Section: Future Progressmentioning

confidence: 99%

Progress in laser guide star adaptive optics and lessons learned

Wizinowich

2012

SPIE Proceedings

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Laser Guide Star (LGS) Adaptive Optics (AO) on large telescopes has recently become a very productive science tool for the astronomical community. Astronomical objects can now be observed at an unprecedented resolution over much of the sky. The science enabled by LGS AO and the capabilities and limitations of these systems will be discussed, along with the lessons learned that can be applied to LGS AO systems on existing and planned telescopes.

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“…• Better understanding of the laser coupling efficiency to sodium [45] and of the sodium layer [46][47] will continue to be developed.…”

Section: Future Progressmentioning

confidence: 99%

Progress in laser guide star adaptive optics and lessons learned

Wizinowich

2012

SPIE Proceedings

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“…The sodium layer evolves slowly: we expect a focus variation of a few tens of nanometers (≤ 0.1 rad) in 1 minute. 13 These variations are negligible in our case. However, meteors can cross the sodium layer and change its altitude quickly in the sensing direction.…”

Section: Simulation Methods and Parametersmentioning

confidence: 51%

LIFT: analysis of performance in a laser assisted adaptive optics

Plantet¹,

Meimon²,

Conan³

et al. 2014

SPIE Proceedings

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Laser assisted adaptive optics systems rely on Laser Guide Star (LGS) Wave-Front Sensors (WFS) for high order aberration measurements, and rely on Natural Guide Stars (NGS) WFS to complement the measurements on low orders such as tip-tilt and focus. The sky-coverage of the whole system is therefore related to the limiting magnitude of the NGS WFS.We have recently proposed LIFT, a novel phase retrieval WFS technique, that allows a 1 magnitude gain over the usually used 2×2 Shack-Hartmann WFS. After an in-lab validation, LIFT's concept has been demonstrated on sky in open loop on GeMS (the Gemini Multiconjugate adaptive optics System at Gemini South). To complete its validation, LIFT now needs to be operated in closed loop in a laser assisted adaptive optics system.The present work gives a detailed analysis of LIFT's behavior in presence of high order residuals and how to limit aliasing effects on the tip/tilt/focus estimation. Also, we study the high orders' impact on noise propagation. For this purpose, we simulate a multiconjugate adaptive optics loop representative of a GeMS-like 5 LGS configuration. The residual high orders are derived from a Fourier based simulation. We demonstrate that LIFT keeps a high performance gain over the Shack-Hartmann 2×2 whatever the turbulence conditions. Finally, we show the first simulation of a closed loop with LIFT estimating turbulent tip/tilt and focus residuals that could be induced by sodium layer's altitude variations.

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“…It is well-suited to studies of mesospheric sodium on timescales relevant for AO. A sodium layer study for LGS AO purposes on time resolutions of tens of seconds has been conducted by Neichel et al (2013) on Cerro Pachón in the southern hemisphere. Their dynamical results agree well with the present 3-year data set.…”

Section: Introductionmentioning

confidence: 99%

High resolution mesospheric sodium properties for adaptive optics applications

Pfrommer

Hickson

2014

A&A

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Context. The performance of laser guide star adaptive optics (AO) systems for large optical and infrared telescopes is affected by variability of the sodium layer, located at altitudes between 80 and 120 km in the upper mesosphere and lower thermosphere. The abundance and density structure of the atomic sodium found in this region is subject to local and global weather effects, planetary and gravity waves and magnetic storms, and is variable on time scales down to tens of milliseconds, a range relevant to AO. Aims. It is therefore important to characterize the structure and dynamical evolution of the sodium region on small, as well as large spatial and temporal scales. Parameters of particular importance for AO are the mean sodium altitude, sodium layer width and the temporal power spectrum of the centroid altitude. Methods. We have conducted a three-year campaign employing a high-resolution lidar system installed on the 6-m Large Zenith Telescope (LZT) located near Vancouver, Canada. During this period, 112 nights of useful data were obtained. Results. The vertical density profile of atomic sodium shows remarkable structure and variability. Smooth Gaussian-shaped profiles rarely occur. Multiple internal layers are frequently found. These layers often have sharp lower edges, with scale heights of just a few hundred meters, and tend to drift downwards at a typical rate of one kilometer every two to three hours. Individual layers can persist for many hours, but their density and internal structure can be highly variable. Sporadic layers are seen reaching peak densities several times the average, often in just a few minutes. Coherent vertical oscillations are often found, typically extending over tens of kilometers in altitude. Regions of turbulence are evident and Kelvin-Helmholtz instability are sometimes seen. The mean value of the centroid altitude is found to be 90.8 ± 0.1 km. The sodium layer width was determined by computing the altitude range that contains a specified fraction of the returned sodium light. We find a mean value of 13.1 ± 0.3 km for the range containing 95% of the photons, with a maximum width of 21 km. The temporal power spectral density of fluctuations of the centroid altitude is well described by a power law having an index that ranges from −1.6 to −2.3 with a mean value of −1.87 ± 0.02. This is significantly steeper than the value of −5/3 that would be expected if the dynamics were dominated by Kolmogorov turbulence, indicating that other factors such as gravity waves play an important role. The amplitude of the power spectrum has a mean value of 34 +6 −5 m 2 Hz −1 at a frequency of 1 Hz, but ranges over two orders of magnitude. The annual means of the index and amplitude show a variation that is well beyond the calculated error range. Long-term global weather patterns may be responsible for this effect.

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Characterization of the sodium layer at Cerro Pachón, and impact on laser guide star performance

Cited by 28 publications

References 19 publications

Progress in laser guide star adaptive optics and lessons learned

Progress in laser guide star adaptive optics and lessons learned

LIFT: analysis of performance in a laser assisted adaptive optics

High resolution mesospheric sodium properties for adaptive optics applications

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