Towards an optical "black hole": surface reshaping for an optimal optical coupling into turbid medium

Light propagation in a turbid medium is typically considered for flat or regular surfaces. However, such an approximation often does not reflect an experimental reality, and, in this report, we attempt to optimize the surface of a scattering medium to improve the optical coupling into the medium. By making conical microchannels in a turbid medium using short-pulsed laser micro-drilling, we show that we were able to substantially increase the photon life-time and diffusion radius in the medium.