Single shot multi spectral transmission matrix measurement of very thick scattering media (Conference Presentation)

After travelling through a disordered medium an ultrashort pulse of light gets completely scrambled both temporally and spatially. Multiple scattering tends to elongate the pulse duration and to distort it spatially, as each spectral component of the pulse generates a different speckle pattern. This mixing results in a complex spatio-temporal speckle pattern. By determining the Multi Spectral Transmission Matrix (MSTM) of the medium, one can achieve full control of transmitted light both in time and space only by exploiting spatial degrees of freedom of a single SLM. This operator is a stack of monochromatic Transmission Matrices (TM), measured for all the spectral components of the pulse. Although this technique has proved its efficiency, its technical complexity precludes its broad dissemination. Primarily, it requires a pulsed laser capable of tunable CW operation to measure all monochromatic TMs. Additionally, the scattering medium needs to be stable during the whole experiment, which is a major limitation for thick media with large number of independent TMs. Here, we report a new technique to parallelize the full MSTM measurement of a highly scattering medium. It speeds up acquisition an order of magnitude, and does not require a tunable source. To this end, a micro-lens array and a diffraction grating are used to encode both spatial and spectral information of the output speckle on a single CMOS camera. We experimentally demonstrate the advantage of the technique by measuring MTSM in very strong scattering regime (N_λ>30) where the conventional method would be impractical.