Pump Probe Experiment for Optical Diagnosis of Very Thick Scattering Media

Scattering media with very high optical density are present in a great variety of application: clouds, paints, spray and biological cells. New optical diagnosis tools developments are very important in order to get in situ characterization without disturbing the sample. The goal of this paper is to describe a new method for determining the Particle Size Distribution (PSD) of a very thick scattering medium. This method is based on Optical Density (OD) measurements for different wavelengths, and a numerical inversion algorithm. The experimental challenge is to operate a light source that is both bright enough and tuneable in order to carry out such measurements. In addition, the scattered light has to be filtered. We will demonstrate that femtosecond spectroscopy overcomes all of these difficulties. A numerical inversion algorithm has been implemented in order to determine the PSD from an OD spectrum.