To exploit photonics technologies for in vivo studies in life science and biomedicine, it is necessary to efficiently deliver light energy to the target objects embedded deep within complex biological tissues. However, light waves diffuse randomly inside complex media due to multiple scattering, and only a small fraction reaches the target object. Here we present a method to counteract the random diffusion and to focus ‘snake-like’ multiple-scattered waves to the embedded target. To realize this, we experimentally identified time-gated reflection eigenchannels that have extraordinarily large reflectance at a specific flight time where most of the multiple-scattered waves have interacted with the target object. By injecting light to these eigenchannels, we achieved more than 10-fold enhancement in light energy delivery compared to ordinary wave diffusion cases. This method works up to depths of approximately 2 times the transport mean free path at which target objects are completely invisible by ballistic optical imaging. This work will lay a foundation for enhancing the working depth of imaging, sensing, and light stimulation.
Ye-Ryoung Lee, Seungwon Jeong, Sungsam Kang, Wonjun Choi, Jin Hee Hong, Jin-Sung Park, Yong-Sik Lim, Hong-Gyu Park, and Wonshik Choi, "Focusing of light energy inside a scattering medium by controlling the time-gated multiple light scattering (Conference Presentation)," Proc. SPIE 10502, Adaptive Optics and Wavefront Control for Biological Systems IV, 105020K (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2286821.5751631622001.
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