This thesis deals with novel approaches to control wave propagation, in particular of light, in opaque scattering materials. We have developed and characterized novel experimental methods for spatially and temporally controlled focusing of ultrashort laser pulses both through and inside random scattering media. For this purpose, we developed the approach of short-pulse wavefront shaping; we spatially shape the wavefront of the pulsed beam, which is incident on the medium, by iteratively optimizing an appropriate feedback signal from the focus. The optimized wavefront couples to the random medium in such a way, that the randomly scattered waves interfere constructively at the intended focus, where they form an intense short pulse. We have devised and implemented two different schemes to provide a feedback signal suitable to sensitize the iterative wavefront shaping optimization for the formation of an ultrashort pulse. In a first experiment, we implement this feedback signal by a time-resolved measurement by heterodyne interferometry, which allows the direct optimization of the field amplitude and one point in space and time. Furthermore, we demonstrate that an indirect measurement of a nonlinear feedback signal provided, e.g., by a second-harmonic generation process, leads to comparable focusing and allows creating the focus deep inside scattering media. Our approaches are applicable to all types of waves. Next to our experiments with light, we demonstrate the extension of our short-pulse wavefront shaping approach to a broadband concept based on an ultrasound experiment. We envision a number of possible applications for our methods, such as in the development of novel imaging techniques for biomedical applications, in performing novel tests to random matrix theory, and in devising new ways to control light in nanophotonic structures and metamaterials for communication technology, sensing and optical computing.
|Award date||20 Sep 2013|
|Place of Publication||Enschede|
|Publication status||Published - 20 Sep 2013|