<title>Using an obliquely incident laser beam to measure optical properties of turbid media</title>

Abstract

ABSTRACT A simple and quick approach was invented to measure optical properties of tissue-like turbid media. A laser beam with oblique incidence to the medium causes the center of the diffusereflectance that is several transport mean free paths away from the incident point to shift from thepoint of incidence. The amount of shift is used to compute the reduced scattering coefficient by asimple formula. This formula is a function of the refractive index of the turbid medium divided bythat of the incident medium and the angle of incidence off the surface normal for a semi-infiniteturbid medium having a much smaller absorption coefficient than the reduced scattering coefficient. For a turbid medium having a comparable absorption coefficient with the reduced scattering coefficient, a revision to the above formula was made. The slope of the diffuse reflectance can beused to compute the penetration depth. Both the computation of the reduced scattering coefficientand penetration depth are based on simple and quick algorithms. The validity conditions of thealgorithms for slabs of turbid media are studied. This technique has potential for non-invasive, invivo, real-time diagnosis of disease or monitoring of treatments.Key words: Tissue optics, turbid media, scattering media, absorption coefficient, reducedscattering coefficient, optical properties, Monte Carlo simulation.