The Slope-Oriented Hadamard scheme for in-lab or on-sky interaction matrix calibration
The correct calibration of the interaction matrix affects the performance of an adaptive optics system. In the case of high-order systems, when the number of mirror modes is worth a few thousands, the calibration strategy is critical to reach the maximum interaction matrix quality in the minimum time. This is all the more true for the E-ELT, for which on sky calibration procedures have to be considered. Here, we first build a tractable interaction matrix quality criterion. We then propose the Slope-Oriented Hadamard scheme which optimizes this quality criterion.We demonstrate that for a given level of quality, the calibration time needed using the Slope-Oriented Hadamard method is ten times less than with a classical Hadamard scheme. These analytical and simulation results are confirmed experimentally on the SPHERE XAO system (SAXO).
Robust real-time control of an adaptive optics system
This research contributes to the understanding of the limitations when designing a robust control real-time system for Adaptive Optics (AO). One part of the research is a new method regarding the evaluation of a Shack-Hartmann wavefront sensor (SHWFS) to enhance the overall performance. The method is presented based on the application of a Field Programmable Gate Array (FPGA) using Connected Component Labeling (CCL) for blob detection. The FPGA has been utilized since the resulting delay is crucial for the general AO performance. In this regard, the FPGA may accelerate the evaluation largely by its parallelism. The developed algorithm does not rely on a fixed assignment of the camera sensor area to the lenslet array to maximize the dynamic range. In extension to the SHWFS evaluation, a new rapid control prototyping (RCP) system based on hard real-time RTAI-patched Linux kernel has been developed. This system includes the required hardware e.g.~the analog output cards and FPGA based frame-grabber. Based upon a Simulink model, accelerated C/C++ code is automatically generated which uses the available parallel features of the processor. A continuative contribution is the application of a robust control scheme using H-infinity methods for designing a controller while considering uncertainty of the identified model. For synthesizing the controller, a special optimization technique called non-smooth mu-synthesis is utilized which minimizes the H-infinity norm while coping with pre-specified controller schemes. Depending on the pre-specified controller scheme, the resulting controller can be computationally costly but the RCP approach is designed to cope with the problem. Based on simulations and according to experiments, the validity of the identified models of the AO setup is assured. At the same time, the enhanced performance of the new RCP setup is demonstrated.
SPHERE: a planet finder instrument for the VLT
Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design of a "Planet Finder" instrument is therefore optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design and expected performance of the SPHERE instrument.