Spatiotemporal Control of Light in Turbid Media

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TitleSpatiotemporal Control of Light in Turbid Media
Publication TypeThesis
Year of Publication2013
AuthorsJ. Aulbach
Date Published09/2013
UniversityUniversity of Twente
Thesis TypePhD
Keywordscondensed matter, disorder, light diffusion, multiple scattering, nonlinear optics, optics, random matrix theory, second harmonic generation, Wavefront shaping

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.



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Dissertation_JochenAulbach.pdf13.48 MB