||In confocal and two photon excitation microscopy, specimen induced aberrations pose a limit to the achievable imaging quality and imaging depth. Diffraction limited imaging could be restored by applying adaptive optics methodologies. Nonetheless, the inclusion of conventional wavefront sensors is nontrivial in such imaging techniques. Henceforth, sensorless adaptive optics methodologies are particularly appealing in this context, due to their relatively easy application to existing microscopes. In such methodologies, the aberration of the wavefront must be estimated by examining related quantities such as the intensity distribution or the image sharpness .
The problem of aberration estimation can be reformulated in a system theoretical framework where Wiener systems are employed. As both the influence of the specimen aberration and that of the active device used for the aberration correction can be assumed to add linearly in phase, the state of the system can be represented by a linear state space equation. Instead, the output of the system is related by a nonlinear function to the state. Henceforth, a nonlinear state estimation problem results.
The student will perform a literature review on the problem of state estimation and nonlinear identification relevant for the two photon microscopy problem. After successful implementation and verification of a selected state estimation methodology in MATLAB, experimental validation can be performed on the real-life test facilities in the Optics Lab of the Delft Center for Systems and Control.
 H. Song, R. Fraanje, G. Schitter, H. Kroese, G. Vdovin, and M. Verhaegen, "Model-based aberration correction in a closed-loop wavefront-sensor-less adaptive optics system," Opt. Express 18, 24070-24084 (2010)