PhD defence Elisabeth Brunner

13 December 2018 12:30 till 14:30 - Location: Aula senaatszaal, Mekelweg 5 - By: DCSC

"Spline-based wavefront reconstruction for Shack-Hartmann measurements"

In the coming decade, a new generation of extremely large-scale ground-based astronomical telescopes (ELTs) will see first light. Increasing the size of the telescope aperture is however only beneficial if the adaptive optics (AO) system, which compensates for turbulence-induced wavefront aberrations, scales accordingly. For the extreme-AO (XAO) systems of the future ELTs, in the order of 10^4–10^5 unknown phase points have to be estimated at kHz range frequencies. Within the AO group of the DCSC, the Spline-based ABerration REconstruction (SABRE) method has been developed. The approach uses bivariate simplex B-spline functions for wavefront reconstruction (WFR) from gradient measurements provided by the Shack-Hartmann (SH) wavefront sensor. The focus of this thesis lies on advancing the SABRE method in terms of computational efficiency and reconstruction accuracy. Founded on the local nature of the B-spline functions, an inherently distributed solution to the WFR problem was developed. A domain decomposition approach allows local computation of B-spline wavefront estimates on the partitions. A parallel implementation of the method for graphics processing units (GPUs) has proven its scalability to application on XAO systems. Further, two approaches are introduced to retrieve additional information of orders higher than the local gradients from the intensity distributions of the SH focal spot pattern. Employing higher degree polynomials, the reconstruction accuracy of the B-spline estimates achieved with a given SH sensor array can now be increased.


Promotor: M. Verhaegen