MANU-CHAO: a laboratory ground-layer adaptive optics experiment

Abstract

We present a laboratory setup of a Ground-Layer Adaptive Optics system. This system is a scaled-down version of the MCAO system of MAD (a MCAO system for the VLT) / LINC-NIRVANA (a Fizeau Imager for the LBT) and measures the wavefront aberrations with 4 pyramids in a layer-oriented fashion with optical co-addition. The laboratory setup contains besides the wavefront-sensing unit a telescope-simulator, a dynamic turbulence generator and a Deformable Mirror for the wavefront correction. We describe the overall system and its single components, open-and closed-loop measurements of the characteristics of a system working in GLAO mode and first results when using a Kalman filter for the control of the wavefront reconstruction process.

A frame decomposition of the atmospheric tomography operator

“…Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Correction of an incoming wavefront by a deformable mirror (left, image taken from [2]) and sketch of an SCAO system (right, image taken from [6]).…”

“…Unfortunately, and in particular since the separation of the NGSs and LGSs is low (e.g., 1 arcmin for MCAO and 3.5 arcmin for MOAO), the problem of atmospheric tomography falls into the category of limited-angle tomography, which is known to be a severely illposed problem [4,21]. In addition, the number of available guide stars is relatively small as well (e.g., 6 LGSs for the ELT), which in combination with the severe ill-posedness makes the reconstruction of the full atmospheric turbulence above the telescope a hopeless endeavour. Hence, one works with the commonly accepted assumption that the atmosphere contains only a limited number of turbulent layers, which are infinitely thin and located at predetermined heights.…”

“…Figure 1.Correction of an incoming wavefront by a deformable mirror (left, image taken from[2]) and sketch of an SCAO system (right, image taken from[6]). …”

The MPIA multipurpose laboratory atmospheric turbulence simulator MAPS

“…MAPS not only allows one to simulate the dynamic effects of the atmospheric turbulence with adjustable wind-speeds, but also to examine the influence of non-conjugated turbulent layers on the measurement and reconstruction process of the ground-layer turbulence. Its repeatability of the turbulent effects furthermore allows a statistically significant comparison of different reconstruction algorithms for AO and MCAO (see Egner et al, 19 these proceedings).…”

Pyramid wavefront sensor using a sequential operation method

“…The PWFS is an attractive option for next generation astronomical adaptive optics systems compared with the Shack-Hartmann wavefront sensor [7,8]. It also acts as a new element in the multilayer conjugate adaptive optics system to solve the problems related with limited field of view [9]. The capability of PWFS to phase and align segmented mirrors has also been described in [10].…”