Optical Properties

The optical properties of tissue reveal characteristics that are useful in differentiating between tissue types and identifying pathological changes. Our research focuses specifically on the refractive index, absorption and scattering properties of biological samples. The index of refraction refers to the speed at which light passes through a material and is usually measured over a large area. As light interacts with small structures of varying refractive index, it is angularly redistributed, or scattered. The scattering coefficient is a function of the index variations at a scale near that of the wavelength of the incident light. This quantity, when added to the absorption coefficient, represents the overall attenuation of the light passing through the material. The attenuation causes an exponential degradation of the incident intensity with depth.

Our laboratory uses a variety of techniques in order to measure these characteristics at multiple wavelengths. Integrating spheres are used to measure the scattering and absorption coefficients of materials by collecting all transmitted and reflected light onto two detectors.

A goniometric instrument, which moves a detector around the sample to collect the redistributed light, yields an angular scattering function. Refractive index measurements are computed based on the analysis of displaced-reflector images created using an OCT system.

Refractive index measurements are computed based on the analysis of displaced-reflector images created using an OCT system.