Focusing of light energy inside a scattering medium by controlling the time-gated multiple light scattering

The efficient delivery of light energy is a prerequisite for the non-invasive imaging and stimulating of target objects embedded deep within a scattering medium. However, the injected waves experience random diffusion by multiple light scattering, and only a small fraction reaches the target object. Here, we present a method to counteract wave diffusion and to focus multiple-scattered waves at the deeply embedded target. To realize this, we experimentally inject light into the reflection eigenchannels of a specific flight time to preferably enhance the intensity of those multiple-scattered waves that have interacted with the target object. For targets that are too deep to be visible by optical imaging, we demonstrate a more than tenfold enhancement in light energy delivery in comparison with ordinary wave diffusion cases. This work will lay a foundation to enhance the working depth of imaging, sensing and light stimulation. The use of a time-gated reflection matrix of a scattering medium, in particular via using singular value decomposition and injecting light into the largest time-gated eigenchannel, can lead to a more than tenfold enhancement in light energy delivery in comparison with ordinary wave diffusion cases.