First-light adaptive optics system for large binocular telescope

Abstract

The paper describes the design of the single conjugate Adaptive Optics system to be installed on the LBT telescope. This system will be located in the Acquisition, Guiding and Wavefront sensor unit (AGW) mounted at the front bent Gregorian focus of LBT. Two innovative key features of this system are the Adaptive Secondary Mirror and the Pyramid Wavefront Sensor. The secondary provides 672 actuators wavefront correction available at the various foci of LBT. Due to the adaptive secondary mirror there is no need to optically conjugate the pupil on the deformable mirror. This allows having a very short sensor optical path made up using small dimension refractive optics. The overall AO system has a transmission of 70 % and fits in a rectangle of about 400x320mm. The pyramid sensor allows having different pupil sampling using on-chip binning of the detector. Main pupil samplings for the LBT system are 30x30, 15x15 and 10x10. Reference star acquisition is obtained moving the wavefront sensor unit in a field of view of 3x2 arcmin. Computer simulations of the overall system performance show the good correction achievable in J, H, and K. In particular, in our configuration, the limiting magnitude of pyramid sensor results more than one magnitude fainter with respect to Shack-Hartmann sensor. This feature directly translates in an increased sky coverage that is, in K band, about doubled with respect to the same AO system using a Shack-Hartmann sensor.

General formalism for Fourier-based wave front sensing

“…Equation 18 will define the effective meta-intensity while the restriction of the phase power series development to its first term, i.e. to the linear intensity I l , will define the linear meta-intensity (see equation 16). We note that this linear meta-intensity cannot be strictly deduced from the intensity on the detector but easily computed by numerical simulations.…”

“…Note that in this case, it is impossible to make m only a function of the two variables f x /λ and f y /λ; it means that the associated WFS is not achromatic. Fortunately, a classical solution to solve this problem exits which consists in using two transparent pyramids attached by their base (Esposito et al 16 ). Such a device allows, in substance, to nullify the first λ-dependent term C of the refractive index.…”

The LBT-AdOpt arbitrator: coordinating many loosely coupled processes

“…Detailed descriptions of the LBT-AdOpt system and follow-ups of its development have been presented many times [1][2][3][4] and are updated in this same conference 5, 6 . The system is essentially subdivided into two largely independent subsystems: a pyramid based Wavefront Sensor 2, 3 (WFS), and an Adaptive Secondary mirror [7][8][9][10][11] (AdSec).…”

Parallel scientific computing environment for adaptive optic simulations

“…This system allows the gain and sampling to be changed in a continuous way, thus enabling a better match of the system performance with variable wavefront aberration than those obtained with the classical Shack-Hartman set-up. The wavefront sensor consists of a fourface flat pyramid (i.e., with vertex angle slightly smaller than 180) made of a transparent material acting as an image splitter [6]. The software tool currently used to simulate the whole process of atmospheric propagation of light, wavefront sensing, wavefront correction and reconstruction, and closing the loop of the AO system in LBT is the CAOS (Code for Adaptive Optics System) software [4].…”