Spatial coherence of light inside three-dimensional media

Spatial coherence

Speckle is maybe the most fundamental interference effect of light in disordered media, giving rise to fascinating physical phenomena and cutting-edge applications. While speckle formed outside a sample is easily measured and analyzed, true bulk speckle, as they appear inside random media, is difficult to investigate directly due to the obvious issue of physical access. Furthermore, its proper theoretical description poses enormous challenges. In a recent paper, we report on the first direct measurements of spatially resolved intensity correlations of light inside a disordered medium, using embedded DNA strings decorated with emitters separated by a controlled nanometric distance 

“We propose a new use for the DNA-based nanoprobes, commonly employed for the characterization of the resolution of a microscope. - declares Marco Leonetti, lead researcher of the CNR Nanotec, first author of the paper - Illuminating the nanoprobes with an optical modulator, it is possible to measure the speckle statistics, and, from that, extract the optical properties in the surrounding of the nanoprobe. The nanoprobes are capable to “beam” the information across of the opaque wall of the scattering sample to the measurements instruments, enabling to get- in-vivo information and avoiding, potentially, more invasive analysis.”

“With this technique, we can see what happens inside tissue without the need of image formation. Instead, we extract the information for the intensity statistics rather than from the angle of incidence on our eye.  - Concludes Giancarlo Ruocco, Coordinator  Professor the Department of Physics of the University Sapienza - There are multiple potential applications, including a future generation of biocompatible nanoprobes capable of providing direct information of the occurrence of local alteration of the tissue in the least accessible areas such as in some neurodegenerative diseases”. 

The new method provides in situ access to fundamental properties of bulk speckles as their size and polarization degrees of freedom. The authors found these properties to deviate significantly from theoretical predictions and explained these unexpected deviations are described in terms of correlations among polarization components and non-universal near-field contributions at the nanoscale.

Marco Leonetti, Lorenzo Pattelli, Simone De Panfilis, Diederik S. Wiersma, and Giancarlo Ruocco



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