OPTICAL-PROPERTIES OF THICK, TURBID MEDIA FROM PICOSECOND TIME-RESOLVED LIGHT-SCATTERING MEASUREMENTS

A computational and experimental investigation is reported regarding t he feasibility of determining optical properties of turbid media from picosecond (PS) time-resolved light scattering measurements in conjunc tion with diffusion theory predictions, Monte Carlo simulations, and o ther appropriate optical measurements. Picosecond time-resolved transm ission measurements were performed using aqueous latex particle suspen sions with and without absorbing dye. Monte Carlo simulations were als o performed to aid in determining limitations of the approach as well as suitable measurement parameters. The system of interest was an opti cally thick plane-parallel, homogeneous slab consisting of an absorbin g, anisotropic scattering medium subject to collimated, pulsed inciden t radiation. The results of comparing Monte Carlo and diffusion theory predictions showed that important pulse parameters, such as long-time asymptotic log slope and RMS pulse width, are given by diffusion theo ry analytical expressions with enough accuracy to be useful for determ ining the unknown optical properties of the medium from time-resolved scattering measurements. These findings were verified using PS time-re solved transmission measurements on aqueous latex particle suspensions . It was also found that the albedo criterion for application of diffu sion theory to time-dependent scattering may be much less restrictive than is usually reported (weak absorption or albedo near one is not ne cessary).