Shaping the angular spectrum of a Bessel beam to enhance light transfer through dynamic strongly scattering media

We prepare a quasi-non-diffracting Bessel beam defined within an annular angular spectrum with a spatial light modulator. The beam propagates through a strongly scattering media, and the transmitted speckle pattern is measured at one point with a Hadamard Walsh basis that divides the ring into N segments (N = 16, 64, 256, 1024). The phase of the transmitted beam is reconstructed with 3-step interferometry, and the intensity of the transmitted beam is optimized by projecting the conjugate phase at the SLM. We find that the optimum intensity is attained for the condition that the transverse wave vector k⊥ (of the Bessel beam) matches the spatial azimuthal frequencies of the segmented ring kϕ. Furthermore, compared with beams defined on a 2d grid (i.e., Gaussian) a reasonable enhancement is achieved for all the k⊥ sampled with only 64 elements. Finally, the measurements can be done while the scatterer is moving as long as the total displacement during the measurement is smaller than the speckle correlation distance.