Effect of an integrating sphere measurement on the distortion of a laser pulse propagating through a turbid medium

Abstract

A focused nanosecond laser pulse produces optical damage to subsurface targets when its intensity is high enough to overcome the required threshold irradiance. However, when the material is highly scattering, the laser pulse irradiance decreases as it propagates through the sample because the temporal pulse profile is stretched due to multiple scattering events. The objective of this work is to determine the transfer function associated to an integrating sphere measurement involving turbid media samples. Integrating spheres are used to measure the total diffuse reflectance and transmittance of homogeneous turbid media samples to retrieve its absorption and scattering coefficients. Reflectance and transmittance measurements, being static properties, are not affected by multiple reflections of light inside the integrating spheres. However, for a time-dependent measurement, such as the temporal profile of a short laser pulse propagating through a turbid medium, the light reflection and multiple scattering events inside the sphere contributes to an additional stretching deformation of the measured temporal pulse profile, which complicates the interpretation of the measurements. In this work we use integrating spheres to analyze the effect of a turbid media on the propagation of a nanosecond laser pulse.