Measurements of channels and time delay of light in strongly scattering media

Abstract

In this thesis measurements of the transport of light through a multiple scattering medium are presented. We experimentally investigate three different eigenmodes of the light field: Transport eigenchannels, time delay eigenstates and scattering invariant modes. We investigate the spectral width and time delay of the transmission channels, which are singular modes of the transmission matrix. We find three transmittance regimes for the spectral width of the transmission channels and find their transmission is only weakly correlated to time delay. The time delay eigenstates are eigenmodes of the Wigner-Smith time-delay matrix. We investigate their time delay eigenvalues, in which we identify modes with a time delay ranging between zero and about three times the Thouless time. Finally, we show scattering invariant modes, which are transmitted with a similar field shape through air and a multiple scattering medium. We also show an iterative digital optical phase conjugation based procedure to find a scattering invariant mode. The observations are based on multispectral transmission matrix measurements that capture a large fraction of the transmission operator.