Real-time turbulence profiling with a pair of laser guide star Shack–Hartmann wavefront sensors for wide-field adaptive optics systems on large to extremely large telescopes

Abstract

Real-time turbulence profiling is necessary to tune tomographic wavefront reconstruction algorithms for widefield adaptive optics (AO) systems on large to extremely large telescopes, and to perform a variety of image post-processing tasks involving point-spread function reconstruction. This paper describes a computationally efficient and accurate numerical technique inspired by the slope detection and ranging (SLODAR) method to perform this task in real time from properly selected Shack-Hartmann wavefront sensor measurements accumulated over a few hundred frames from a pair of laser guide stars, thus eliminating the need for an additional instrument. The algorithm is introduced, followed by a theoretical influence function analysis illustrating its impulse response to high-resolution turbulence profiles. Finally, its performance is assessed in the context of the Thirty Meter Telescope multi-conjugate adaptive optics system via end-to-end wave optics Monte Carlo simulations.

Turbulence modeling and Kalman prediction for the control of large AO systems

“…Similarly to [15] we consider Θ, the matrix formed by the {θ v } column vectors, where each of the {θ v } is associated to a possible layer velocity v: only the velocities considered in Θ can be detected. Usually the choice of the velocities to be considered is restricted to those that have a peak (or at least a value significantly greater than 0) associated in ζ e (·, ·, ·) (as in (14)).…”

“…However, differently from [15] and [27], instead of considering θ v l only for values associated to (u, v, k) where k ∈ {1, . .…”

“…velocities and strengths of the turbulent layers) provided by the proposed method can be particularly useful in the multi-conjugate AO system case, however they can be exploited also in the AO case in order to compute the parameters of the considered temporal model of the turbulence. The approach used in this paper is similar to the SLODAR (SLOpe Detection And Ranging) technique, and in particular to those in [15], [9], [27]: the rationale is that of estimating the characteristics of the turbulence layers from the spatio-temporal correlations of the turbulence. The layers are spatially (partially) decorrelated in order to ease such task.…”

Simulation model based approach for long exposure atmospheric point spread function reconstruction for laser guide star multiconjugate adaptive optics

“…This profile can be estimated either offline by postprocessing the cross-covariance measurement matrix of a pair of LGSs from the multi-LGS constellation, or directly online. Such a turbulent profiling method has been demonstrated in simulations [21] and on the sky at the Gemini South telescope [22]. We will use superscript "mod" to indicate data extracted from (or quantities related to) the simulation model (quantities without this superscript are extracted from the real system).…”

Retrieval of Cn2 profile from differential column image motion lidar using the regularization method

“…Knowledge of the optical turbulence profile becomes a key issue in wide-field adaptive optics (WFAO) systems [1,2] , free-space optical (FSO) communication [3,4] , and laser beam propagating through the atmosphere [5,6] . Several approaches have been proposed to measure the C 2 n profile.…”