Light propagation in two-layer tissues with an irregular interface

Determination of the rough interface parameters using the self-imaging effect

In this work, a linear grating is used to project a periodic light intensity distribution on a rough interface, and the near field transmitted light scattering is studied. It is shown theoretically that the intensity in the Fresnel regime depends on statistical properties of the rough interface and the light intensity period. The self-image contrast exponentially depends on the interface height-height correlation function. The correlation is obtained in terms of multiplication of the self-image number and the period of the light intensity distribution. Therefore, the roughness and the correlation length of the interface can be obtained by determining the contrast of the self-images when the light intensity period is smaller than the interface correlation length. For periods longer than twice the correlation length, the contrast measurements only provide the interface roughness. In experimental studies, the roughness of interfaces is determined by square gratings with periods much longer than the correlation lengths. The rough interfaces are prepared by roughening sheet glass by powders of different grit numbers. The results for different gratings and light wavelengths are quite consistent.

Fast numerical method for electromagnetic scattering from an object above a large-scale layered rough surface at large incident angle: vertical polarization

A fast numerical method has been proposed in this paper for calculating the electromagnetic scattering from a perfectly electric conducting object above a two-layered dielectric rough surface. The focus in this study is large incidence. The parallel fast multipole method is combined with the method of moments for fast implementation of the scattering from this composite model. The biconjugate gradient method is adopted to solve the unsymmetrical matrix equation and parallelized. The simulating time and parallel speedup ratio with different processors are provided. Several numerical results are shown and analyzed to discuss the influences of the parameters of the rough surface, the object, and the intermediate medium on the bistatic scattering.

Quantification of the optical properties of two-layer turbid materials using a hyperspectral imaging-based spatially-resolved technique

Recent research has shown that a hyperspectral imaging-based spatially-resolved technique is useful for determining the optical properties of homogenous fruits and food products. To better characterize fruit properties and quality attributes, it is desirable to consider fruit to be composed of two homogeneous layers of skin and flesh. This research was aimed at developing a nondestructive method to determine the absorption and scattering properties of two-layer turbid materials with the characteristics of fruit. An inverse algorithm along with the sensitivity coefficient analysis for a two-layer diffusion model was developed for the extraction of optical properties from the spatially-resolved diffuse reflectance data acquired using a hyperspectral imaging system. The diffusion model and the inverse algorithm were validated with Monte Carlo simulations and experimental measurements from solid model samples of known optical properties. The average errors of determining two and four optical parameters were 6.8% and 15.3%, respectively, for Monte Carlo reflectance data. The optical properties of the first or top layer of the model samples were determined with errors of less than 23.0% for the absorption coefficient and 18.4% for the reduced scattering coefficient. The inverse algorithm did not give acceptable estimations for the second or lower layer of the model samples. While the hyperspectral imaging-based spatially-resolved technique has the potential to measure the optical properties of two-layer turbid materials like fruits and food products, further improvements are needed in determining the optical properties of the second layer.

Solution of transport equations in layered media with refractive index mismatch using the PN-method

The PN-method is a spectral discretization technique used to obtain numerical solutions to the radiative transport equation. To the best of our knowledge, the PN-method has yet to be generalized to the case of refractive index mismatch in layered slabs used to numerically simulate skin. Our main contribution is the application of a collocation method that takes into account refractive index mismatch at layer interfaces. The stability, convergence, and accuracy of the method are established. Example calculations demonstrating the flexibility of the method are performed.

Determination of height distribution on a rough interface by measuring the coherently transmitted or reflected light intensity

In this work it is shown theoretically and examined experimentally that the measurement of coherently transmitted or reflected monochromatic light intensity from a randomly rough interface as a function of incident angle provides the height distribution on the interface. It is also shown that the spectrum of coherently transmitted or reflected light from a rough interface is modified and the modified spectrum yields the height distribution. The experimental results obtained by applying both methods, in transmission and reflection, on rough surfaces prepared by roughening the sheet glasses by powders of different grain sizes are quite consistent. In addition, the effect of the surrounding medium's refractive index on the roughness measurement is studied by immersing the samples into liquids of different refractive indices. Also, the application range and limitations of the introduced methods are discussed.