Spatial irradiance is a defining characteristic of radiation during the thermal impact of a laser beam on biological tissues, powders, and other scattering media. The provides a theoretical consideration of multiple light scattering in the volume of a semi-infinite diffuse scattering medium (DSM). Calculations are made for pressed dielectric powders with refractive indices n = 1.47, 1.72, and 2.00 at a wavelength of 1.06 μm (the first harmonic of a neodymium laser). The diffuse reflectance coefficients ρ(1 – Λ) calculated by the Monte Carlo method and in the Kubelka–Munk approximation are compared. A linear relationship is established between the spatial irradiance in DSM volume and the diffuse reflectance coefficient. The precisions and applicability limits of the original and corrected Kubelka–Munk formulas are determined. A complex relationship is ascertained between the single scattering albedo Λ and the angular dependence of a photon flux incident on the DSM–air interface f(α). In particular, it was shown that for Λ → 1 and isotropy scattering, f(α) = cos(α), where a is the photon incidence angle. The results can be used for the development of methods for determining spatial irradiance and, for example, in laser medicine.
light scattering, diffuse scattering media, Monte Carlo method, Kubelka–Munk formula, spatial irradiance
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