Propagation of Femtosecond White-Light Continuum Pulse in Polymer Latex Powder Investigated by Optical Kerr Gate and Time-Resolved Diffuse Reflectance Spectroscopy

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Abstract
Propagation of a femtosecond white-light continuum pulse (350 fs) in poly (methyl methacrylate) (PMMA) latex powders with particle diameters of 1, 5, 20, 60, and 100 µm was investigated by means of an optical Kerr gate and time-resolved diffuse reflectance spectroscopy, which is a pump-probe technique for multiple light scattering materials. The temporal profile of a diffuse reflected light pulse from the powder and the temporal response of transient absorption of the powder doped with an organic molecule were measured. The Kubelka-Munk model was extended to address the propagation of a short light pulse, and its numerical simulations reproduced both experimental results quite well. It is suggested that in a dense scattering medium such as powder, an effect that light is confined or proceeds in a twisted manner is of importance. Fitting the experimental data with the diffusion theory was unsuccessful, which is also discussed.