Non-invasive Wavefront Shaping for Focusing Light Inside and Behind Biological Scattering Medium

Optical wavefront shaping is one of the most effective techniques in focusing light inside a scattering medium. Unfortunately, most of these techniques require direct access to the scattering medium or need to know the scattering properties of the medium beforehand. Through our scheme we develop a novel concept in which both the illumination and the detection is on the same side of the inspected object. We model the scattering medium being a biological tissue as a Matrix having mathematical properties matched to the physical and biological aspects of the sample. In our adaptive optics scheme, we aim to estimate the scattering function and thus to encode the wavefront of the illuminating laser light source using DMD (Deformable Mirror Device) with an inverse scattering function of the scattering medium, such that after passing its scattering function a focused beam is obtained. The estimation of the scattering is done by illuminating the medium and in parallel collecting the back reflected light and analyzing its wavefront via off-axis holography (phase and amplitude). We optimize the pattern to be displayed on the DMD using Particle Swarm Algorithm. Hence, we have a map of all the distributions to be displayed in the DMD for focusing inside scattering medium per pixel. Thus, after applying the right beam shaping an imaging of objects behind scattering medium as biological tissue can be made possible. As first proof of concept we experimentally show that we obtain a focused spot behind a biological scattering medium (a tissue) in amplitude modulation scheme using a DMD.