Light Control through Highly Scattering Media

Conkey, Donald Benjamin

Graduate Thesis Or Dissertation

Light Control through Highly Scattering Media Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/sb397843p

Abstract

Imaging through opaque, highly scattering walls is a long sought after capability with potential applications in a variety of fields, such as biomedical imaging. The use of wavefront shaping to compensate for scattering has recently brought a renewed interest as a potential solution to this problem. This method relies on the ability to shape an incident wavefront to pre-compensate for scattering, thus providing light control through a scattering layer. In order for these techniques to begin to extend the imaging depth inside of living biological tissue several constraints must be overcome. As living biological tissue is dynamic these techniques must be able to optimize fast enough to overcome the dynamic nature of the tissue. Also key to the practicality of overcoming scattering is focusing light without direct access behind the scattering wall. This thesis presents means of overcoming these limitations through novel optimization algorithms, wavefront shaping for high-speed modulation, and photoacoustic feedback and imaging behind a scattering layer. A genetic algorithm (GA) is applied for wavefront optimization as a means of enabling parallel mode optimization to increase the speed of the optimization procedure. The results presented show that not only does the GA optimize more quickly, it is more robust in low signal-to-noise (SNR) environments than other optimization algorithms. The low SNR performance is critical to high speed performance, because SNR decreases with the integration time. The GA wavefront optimization is extended towards more complex light control problems, specifically multi-color image projection through scattering layers.

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