Experimental assessment of the effective-medium approach for disordered monolayers of particles with high scattering losses.

The validity of using an effective-medium approach (EMA) to model the reflectivity of a disordered monolayer of particles that scatter light significantly is tested experimentally. To achieve this, we measured the optical reflectivity versus the angle of incidence in an internal reflection configuration of a disordered monolayer of polymeric particles with negligible optical absorption and a diameter of about half a wavelength (size parameter of 1.2) deposited on a glass-air interface.

Probing bio-tissue films by optical internal reflectivity: modeling and measurements.

In this paper, we develop a detailed theoretical model for the optical reflectivity of a bio-tissue film confined between two flat interfaces based on the anomalous-diffraction approximation. We consider bio-tissue films consisting of a few layers of spheroidal cells surrounded by extracellular medium. We explore numerically the predictions of our model and compare them with simple effective medium theories, sometimes used as a first attempt to understand the optical properties of biological media.

Analysis of wavelength-scale 1D depth-dependent refractive-index gradients at an interface by their effects on the internal reflectance near the critical angle.

Light's internal reflectivity near a critical angle is very sensitive to the angle of incidence and the optical properties of the external medium near the interface. Novel applications in biology and medicine of subcritical internal reflection are being pursued. In many practical situations, the refractive index of the external medium may vary with respect to its bulk value due to different physical phenomena at surfaces.

Optical reflectivity of an interface with random refractive-index-contrast patterns.

We develop simple models for the optical reflectivity of an interface in optical contact with random media consisting of discrete volumes of arbitrary form and different refractive indices. Examples of interest are surfaces sprinkled with microdroplets or an interface with biological cells adhered to it at random locations. We focus our attention to the case of internal reflectivity, in which the incidence medium has a larger refractive index than the refractive indices at the other side of the interface.

Analytical approximation to the complex refractive index of nanofluids with extended applicability.

Currently, there are available a few simple analytical approximations to the complex effective refractive index that may be used for nanofluids. Namely, the Maxwell Garnett mixing formula with scattering corrections, the Maxell Garnett Mie approximation, the Foldy-Lax approximation and the small particle limit of the quasi-crystalline approximation. These approximations are valid either for very small nanoparticles (below a few nanometers in radius) or for very dilute nanofluids (below about 1% in particles' volume fractions) and therefore, do not cover the whole domain of particle suspensions referred to as nanofluids.