The use of sodium layer density anisotropies to fully measure the atmospheric turbulence, including tip-tilt, focus, and higher order aberrations

Noelia Martinez; Luis Fernando Rodríguez Ramos

doi:10.1117/12.2560784

13 December 2020 The use of sodium layer density anisotropies to fully measure the atmospheric turbulence, including tip-tilt, focus, and higher order aberrations

Noelia Martinez, Luis Fernando Rodríguez Ramos

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Proceedings Volume 11448, Adaptive Optics Systems VII; 114481V (2020) https://doi.org/10.1117/12.2560784
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Abstract

It is well known that Adaptive Optics (AO) observations do require the availability of natural stars (beside laser guide stars - LGSs) to obtain the tip-tilt and focus information of the atmospheric turbulence. Bright natural stars are not always available imposing the ultimate limit to the AO technology due to the small technical field planned for 40m range telescopes. The use of multiple LGSs, with their respective wavefront sensors and tomographic computations, requires the proper reconstruction of the turbulence column adding significant complexity and cost to the Adaptive Optics systems. Precise knowledge of the tip-tilt information is extremely useful for the accurate pointing of lasers in groundto-space optical communications and in space situational awareness applications. In these contexts the tip-tilt information cannot be obtained from natural stars. Our group have proposed an alternative way of measuring all relevant values of the atmospheric turbulence, specifically including tip-tilt, focus and also higher order aberrations, and tomographic information based on the use of the foreseen density anisotropies in the sodium layer. Results of an analysis using the available information about sodium layer profiles will be presented, showing up to what point anisotropies with the proper spatial and time scales could be expected. The requirements of a laser launch system capable of illuminating uniformly the metapupil at the height of the Na layer are identified and special attention is paid to the required laser power. The extended object generated at the Na-Layer should then be analysed with a wavefront sensor suited to that characteristic. The plenoptic camera is the potential candidate under study in this paper.

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Noelia Martinez and Luis Fernando Rodríguez Ramos "The use of sodium layer density anisotropies to fully measure the atmospheric turbulence, including tip-tilt, focus, and higher order aberrations", Proc. SPIE 11448, Adaptive Optics Systems VII, 114481V (13 December 2020); https://doi.org/10.1117/12.2560784

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KEYWORDS

Sodium

Anisotropy

Atmospheric turbulence

Adaptive optics

Stars

Wavefront sensors

Computed tomography

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