Optical Coherent Reflection from a Confined Colloidal Film: Modeling and Experiment

Abstract

We study the optical reflectivity of confined colloidal films as a function of the angle of incidence in an internal reflection configuration. Two effective medium models and an extended coherent-scattering model for thin colloidal films are compared against experimental measurements with gold, latex, and titanium dioxide colloids. A derivation of the coherent scattering model for confined colloidal films used in this work is presented in a comprehensive way. The model lies within the framework of the multiple-scattering theory and is valid for any angle of incidence and for colloids of small or large particles compared to the wavelength of light, however, only for small and moderately small particles' volume fraction. Reflectivity versus angle of incidence curves for an opaque colloidal film in an internal reflection configuration show the effects of two critical angles. Within the two critical angles, there is a high sensitivity to the presence of colloidal particles, while the volume of colloidal samples needed is in the microliter range. Upon comparing theory with experiment, no model fitting was done in any case. The experimental setup and its calibration procedure are discussed. The results provide physical insight into applications involving optical properties of colloidal systems.

Effective medium theory and its limitations for the description of MoO3 films doped with nanoparticles

“…To corroborate this, it will be shown what happens to the reflectance and the transmittance of doped MoO 3 thin films under the oblique incidence. So, the reflection coefficient simulation [17] is given by the following equation,…”

“…There are several effective medium theories, which can be used. In this manuscript, the one which will be compared with the one that was proposed by vdH is the Maxwell Garnett model (MGM) [17,20], which is given by…”

Impact of Fat Content and Lactose Presence on Refractive Index in Different Types of Cow Milk

“…The exploration of the optical properties of a medium is deeply rooted in the meticulous analysis of its refractive index, a fundamental parameter that indicates the extent to which the speed of light is delayed upon passing through the medium [1][2][3][4][5][6][7][8][9][10]. This significant parameter is a cornerstone in understanding how light interacts with and traverses through various mediums.…”

“…Snell's law is a relationship that describes how light refracts as it passes through a flat interface. Fresnel coefficients represent the proportion of incident light reflected and transmitted at the interface between two media with different refractive indices or interfaces [4,12].…”

“…As already mentioned, the total internal reflection plays a crucial role in the experiment, representing a fundamental optical phenomenon wherein all incident light is reflected beyond a specific angle of incidence known as the critical angle [1][2][3][4][5][6][7][8]15].…”