Non-invasive Imaging Through a Scattering Wall

Abstract

! Antonio M. Caravaca-Aguirre, Donald B. Conkey, Jacob D. Dove, Hengyi Ju, Todd W. Murray and Rafael Piestun 1Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado, 80309, USA 2Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, 80309, USA ! We investigate the problem of optical non-invasively imaging through scattering media without the use of the so-called memory effect, namely allowing for thick and highly scattering obstacles. A photoacoustic (PA) signal, consisting of the integration of PA emissions from multiple speckle grains, is used as optimization feedback for focusing through such a scattering material. We use a liquid-crystal spatial light modulator (LC-SLM) to modulate the input wavefront and optimize the PA response using a genetic algorithm [1]. The spatially non-uniform sensitivity of an ultrasound transducer to the PA emission from multiple speckles results in the enhancement of a single speckle creating a sub-acoustic optical focus [2]. The optical focus is used to reconstruct sub-acoustic resolution images of a bee wing scanned behind a diffusing wall. Figure 1 compares the PA image under three different illuminations: uniform illumination (Fig. 1a) where the diffuser is removed, random speckle illumination where a random phase is projected onto the SLM (Fig. 1b), and optimized illumination (Fig. 1c). After optimization, the signal strength improved by a factor of 10 versus the random speckle field revealing interesting complex structure and significant resolution and signal improvement. Figure 1c shows that even the bee wing hairs are individually resolved. !