<title>Influence of multiple light scattering on a photoacoustic signal</title>

Abstract

Photoacoustic spectroscopy is powerful method of investigation of absorption spectra of scattering media. This method was successfully applied for investigation of different biotissues. However the multiple scattering is essential in these media. It disturbs the output photoacoustic signals. So it is necessary take this phenomenon into account. The purpose of our work is to analyze the variations of photoacoustic signal versus the multiplicity of light scattering. Calculations are held for the model monodisperse spherical particles. Mie theory was applied to describe scattering by single spherical particle. The case of Gaussian profile beam was considered. Monte- Carlo method was used to calculate the photons trajectories in three dimension space. Such events as photon absorption, scattering and reflection from the sell walls was evaluated by random numbers with appropriate probability density. Angular dependence of probability density of the photon scattering is determined in terms of Mie theory for depolarized light. So we define coordinates of photon's collision and absorption points. It enables us to determine the spatial distribution of the points of photon absorption, which depends on the shapes of scattering volume and beam profile. These calculations were made for the model of former elements of blood. It was shown that the multiple scattering varies the absorption profile of the beam. Since multiplicity of light scattering depends on the wavelength of incident light, then absorption spectrum is disturbed. The depth of light penetration into the medium appears to be essentially smaller in the case of short wavelengths.