Periodic Reporting for period 1 - SMART (Scattering Matrix Approach in Reflection applied to Turbid media)
Periodo di rendicontazione: 2017-08-18 al 2019-08-17
We approach this theme with two related sub-topics:
(a) Deep imaging with classical waves (optics and acoustics) in biological (i.e. inhomogeneous) media.
(b) A fundamental study of extreme strong scattering of light.
The objectives are to develop superior imaging and characterization approaches based on (i) incoherent (low power) illumination and (ii) the measurement and manipulation of a matrix of responses between multiple inputs and outputs to the medium. The development of these sub-projects in parallel helps to advance the experimental and post-processing techniques of each. We have been able to demonstrate improved optical imaging with a SMART-OCT system in optics (an OCT-like imaging with low-coherence illumination, improved resolution and depth capabilities compared to OCT) and ultrasonic imaging (deeper imaging through strong aberration, and new contrasts for alternate characterization). We have developed post-processing techniques to image through areas of aberration and multiple scattering in biological media. We have also demonstrated that materials which scatter light exceptionally strongly can be investigated using a similar low coherence, multi-input-output imaging approach.
The fundamental sub-project consisted of the development of an experiment to study materials in which light is extremely strongly scattered, resulting in very slow wave transport (and possibly Anderson localization). Such samples were created (compressed pastilles of TiO2 powder), and were studied with the experimental setup. Results were compared with theoretical predictions to determine whether Anderson localization had taken place and to measure the diffusion coefficient for each sample. One article is about to be submitted on this work.
Results were disseminated to the scientific community via nine conference presentations, and to the public via outreach activities.
For the fundamental sub-project, we did not observe Anderson localization of light in the studied samples, despite them being some of the best candidates in which to observe this phenomenon. This finding, however, agrees with more recent theoretical predictions which are pessimistic about the very existence of this phenomenon for light in compressed powders. We have demonstrated the utility of this setup for the study of other such candidates, and for the quantification of light transport parameters in media, despite the eventual presence of absorption or non linear effects. Our experimental approach enables spatiotemporal observations of extremely slow light, measuring diffusion coefficients of D ~ 1 m^2/s.