Effect of the gradient of complex refractive index at boundary of turbid media on total internal reflection

Complex refractive index of normal and malignant human colorectal tissue in the visible and near-infrared

A multi-wavelength prism coupling refractometer is utilized to measure the angular reflectance of freshly excised human intestinal tissue specimens. Based on reflectance data, the real and imaginary part of the refractive index is calculated via Fresnel analysis for three visible (blue, green, red) and two near-infrared (963 nm and 1551 nm) wavelengths. Averaged values of the complex refractive index and corresponding Cauchy dispersion fits are given for the mucosa, submucosa and serosa layers of the colorectal wall at the normal state. The refractive constants of tumorous and normal mucosa are then cross-compared for the indicative cases of one patient diagnosed with a benign polyp and three patients diagnosed with adenocarcinomas of different phenotype. Significant index contrast exists between the normal and diseased states, indicating the potential use of refractive index as a marker of colorectal dysplasia.

Measurement of complex refractive index of turbid media by scanning focused refractive index

We present the application of scanning focused refractive index microscopy in the complex refractive index measurement of turbid media. An extra standard scattering layer is placed in front of the detector to perform scattering transformation on the reflected light. The principle of the scattering transformation is elaborated theoretically. The influence of the sample scattering is deeply and effectively suppressed experimentally. As a proof of the feasibility and accuracy of the proposed method, we demonstrate experimental data of 20% and 30% Intralipid solutions that are commonly used as phantom media for light propagation studies.

Analysis of reflectance curve of turbid media and determination of the non-surface complex refractive index

Based on the theory of Goos-Hänchen shift and its continuity near the critical angle, we introduce the concept of penetration depth below the critical angle, and obtain the general formula of reflectance using the gradient complex refractive index multilayered model. Compared with the fitting curve with Fresnel's Formula, our calculated results are more consistent with experimental results of Intralipid solution and the suspension of rutile TiO(2) powder. Combining the change of penetration depth near the critical angle with our model, we also reveal the essence of a simple method used to obtain the non-surface complex refractive index of turbid media.