Light propagation in turbid and condensed media.

摘要

The goal of this thesis is to study scattering and transmission of ultrashort optical pulses in turbid and condensed media. Time-resolved polarization, Brillouin precursor propagation and the formation of periodic spatial filament distribution are discussed. Applications of the results of this research will be in medical imaging and free-space optical communications.; In this thesis, I first developed an analytical solution for the time-dependent polarized photon transport equation in a scattering medium using cumulant expansion. By terminating at the second order, I have derived an explicit expression of the polarized light distribution function. Our numerical time-resolved backscattering measurement and results presented a novel circular polarization memory effect in the backscattering from medium containing large size of particles. The application of polarization memory effect in imaging through turbid medium is demonstrated.; I also conducted experiments on ultrashort optical pulses propagation through scattering media. Time-resolved profiles of the transmitted light with parallel and perpendicular to incident polarization are simultaneously measured. Polarization analysis was used to extract coded information buried within the multiple scattering profile from the early ballistic and snake components passing through the turbid medium.; Generation, propagation and attenuation of Brillouin precursor in a dielectric (dispersive and attenuative) medium described by Lorentz model are of interest since controlling of precursor could enhance medical imaging and also has significant applications for the military. I numerically evaluated the contribution of dispersion and absorption in the formation of Brillouin precursor and proposed a feasible way to observe it in THz region. We disproved a recent claim of observing optical precursor in water and gave an alternative explanation to the distortion of small overtone absorption band on optical pulse.; Nonlinear propagation of ultrafast laser pulse and supercontinuum (SC) generation in bulk materials are also been discussed. Periodic formation of ultraintense light filaments, which has markable transmission properties through optically dense media, are induced with diffraction component. Fringes and rings interference patterns are observed and contributed to the coherent properties of multiple supercontinuum sources.