Focusing Light through Turbid Media: Methods and Imaging Applications

Imaging in complex media such as highly scattering tissue remains one of the great challenges of modern optics. While propagating through the medium, light is multiple scattered and its wavefront gets strongly distorted. As a result, the image of an object hidden behind a turbid layer will be blurred or even completely unrecognizable. On the other hand, strong scattering also affects incident light when focusing through the medium and, thus, limits the generation of a well-defined light-distribution at the hidden sample. The recent emergence of high-resolution liquid-crystal devices allows for spatial manipulation of the optical wavefront down to length-scales of a few microns. This kind of modulation is capable to compensate for scattering effects and, therefore, to focus the light at objects hidden behind the turbid medium. In a second step, the spatial light modulator may also be employed to shift the location of the focal spot and thus to raster-scan the hidden object for imaging. In our contribution, we investigate different methods employed in our laboratory for focusing light through turbid media and present recent results in imaging of objects hidden behind such layers.