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Innovative optical designs allow tackling the spot elongation issues in Shack-Hartman based laser guide star wavefront sensors. We propose two solutions using either a combination of two arrays of freeform microlenses, or a combination of freeform optics, to perform a shrinkage of the laser spots as well as a magnification of the SH focal plane. These approaches will drastically reduce the number of needed pixels, thus making possible the use of existing detectors. We present the recent advances on this activity as well as the estimation of performance, linearity and sensitivity of the compressed system in presence of aberrations.

The resolution of coronagraphic high contrast exoplanet imaging devices such as SPHERE is limited by quasistatic aberrations. These aberrations produce speckles that can be mistaken for planets in the image. In order to design instruments, correct quasi-static aberrations or analyze data, the expression of the point spread function of a coronagraphic telescope in the presence of residual turbulence is useful. We have derived an analytic formula for this point spread function. We explain physically its structure, we validate it by numerical simulations and we show that it is computationally efficient.

In this article, we compare a set of Wave Front Sensors (WFS) based on Fourier filtering technique. In particular, this study explores the "class of pyramidal WFS" defined as the 4 faces pyramid WFS, all its recent variations (6, 8 faces, the flattened PWFS, etc.) and also some new WFSs as the flattened cone WFS or the 3 faces pyramid WFS. In the first part, we describe such a sensors class thanks to the optical parameters of the Fourier filtering mask and the modulation parameters. In the second part, we use the unified formalism develop in Fauvarque et al. 1 to create a set of performance criteria: size of the signal on the detector, efficiency of incoming flux, sensitivity, linear range and chromaticity. In the third part, we show the influence of the previous optical and modulation parameters on these performance criteria. This exhaustive study allows to know how to optimize the sensor regarding to performance specifications. We show in particular that the number of faces has influence on the number of pixels required to do the wave front sensing but no influence on the sensitivity and linearity range. To modify these criteria, we show that the modulation radius and the apex angle are much more relevant. Moreover we observe that the time spent on edges or faces during a modulation cycle allows to adjust the trade-off between sensitivity and linearity range.

Over the last few years the Laboratoire d'Astrophysique de Marseille (LAM) has been heavily involved in R&D for adaptive optics systems dedicated to future large telescopes, particularly in preparation for the European Extremely Large Telescope (E-ELT). Within this framework an investigation into a Pyramid wave-front sensor is underway. The Pyramid sensor is at the cutting edge of high order, high precision wave-front sensing for ground based telescopes. Investigations have demonstrated the ability to achieve a greater sensitivity than the standard Shack-Hartmann wave-front sensor whilst the implementation of a Pyramid sensor on the Large Binocular Telescope (LBT) has provided compelling operational results.1, 2 The Pyramid now forms part of the baseline for several next generation Extremely Large Telescopes (ELTs). As such its behaviour under realistic operating conditions must be further understood in order to optimise performance. At LAM a detailed investigation into the performance of the Pyramid aims to fully characterise the behaviour of this wave-front sensor in terms of linearity, sensitivity and operation. We have implemented a Pyramid sensor using a high speed OCAM2 camera (with close to 0 readout noise and a frame rate of 1.5kHz) in order to study the performance of the Pyramid within a full closed loop adaptive optics system. This investigation involves tests on all fronts, from theoretical models and numerical simulations to experimental tests under controlled laboratory conditions, with an aim to fully understand the Pyramid sensor in both modulated and non-modulated configurations. We include results demonstrating the linearity of the Pyramid signals, compare measured interaction matrices with those derived in simulation and evaluate the performance in closed loop operation. The final goal is to provide an on sky comparison between the Pyramid and a Shack-Hartmann wave-front sensor, at Observatoire de la Cote d'Azur (ONERA-ODISSEE bench). Here we present the adaptive optics setup at LAM and latest experimental and modelling results. The loop is closed on different static wave-front errors: the initial shape of the deformable mirror (DM) and a turbulent-like shape projected onto the DM. The results demonstrate a Pyramid closed loop performance of 7–8nm rms wave-front error compared to a reference at surface.

We propose two methods to characterize the Non-Common Path Aberrations (NCPA) on the TMT/NFIRAOS system; these techniques are known as Phase Diversity and Focal Plane Sharpening. We demonstrate the feasibility of these techniques on an experimental bench. We also explore the operational effects of Phase Diversity and how it might be best applied to a NFIRAOS-like system. In particular we explore the technique of single image Phase Diversity along with the effects of i) estimating either Zernike modes or Disk Harmonics, ii) using multiple diverse images, and iii) using diversities other than focus. These operational considerations are explored in a simulation of the NFIRAOS system and we aim to find the best estimation of the NFIRAOS NCPA in the presence of different levels of noise. We find a realistic estimation of NFIRAOS NCPA would be with multi-image Phase Diversity - with focus-diverse images sampled at asymmetric positions on either side of the focal plane (with no estimation of the object).

HARMONI is a visible and near-infrared integral field spectrograph designed to be a first-light instrument on the European extremely large telescope. It will use both single-conjugate and laser tomographic adaptive optics to fully exploit high-performance and sky coverage. Using a fast AO modelling toolbox, we simulate anisoplanatism effects on the point spread function of the single-conjugate adaptive optics of HARMONI. We investigate the degradation of the correction performance with respect to the off-axis distance in terms of Strehl ratio and ensquared energy. In addition, we analyse what impact the natural guide source magnitude, AO sampling frequency and number of sub-apertures have on performance. We show, in addition to the expected PSF degradation with the field direction, that the PSF retains a coherent core even at large off-axis distances. We demonstrated the large performance improvement of fine tuning the sampling frequency for dimer natural guide stars and an improvement of approx. 50% in SR can be reached above the nominal case. We show that using a smaller AO system with only 20x20 sub-apertures it is possible to further increase performance and maintain equivalent performance even for large off-axis angles.

GALACSI is the Adaptive Optics (AO) system serving the instrument MUSE in the framework of the Adaptive Optics Facility (AOF) project. Its Narrow Field Mode (NFM) is a Laser Tomography AO (LTAO) mode delivering high resolution in the visible across a small Field of View (FoV) of 7.5" diameter around the optical axis. From a reconstruction standpoint, GALACSI NFM intends to optimize the correction on axis by estimating the turbulence in volume via a tomographic process, then projecting the turbulence profile onto one single Deformable Mirror (DM) located in the pupil, close to the ground. In this paper, the laser tomographic reconstruction process is described. Several methods (virtual DM, virtual layer projection) are studied, under the constraint of a single matrix vector multiplication. The pseudo-synthetic interaction matrix model and the LTAO reconstructor design are analysed. Moreover, the reconstruction parameter space is explored, in particular the regularization terms. Furthermore, we present here the strategy to define the modal control basis and split the reconstruction between the Low Order (LO) loop and the High Order (HO) loop. Finally, closed loop performance obtained with a 3D turbulence generator will be analysed with respect to the most relevant system parameters to be tuned.