Light can be trapped in localized modes in some dielectric microstructures that are similar to the localized wave functions of electrons in disordered solids as described by Anderson localization. Such a phenomenon is governed by the material properties, mean free path length, associated wavelength, and interference effects. The strength of such localized modes in a disordered optical medium is defined in a unique parameter, by the authors of this article in Optics Express
, as inverse participation ratio (IPR). In a weakly disordered medium, the degree of structural disorder relates to local refractive index fluctuations (or mass density variations) and is proportional to this unique parameter. The method starts from acquisition of confocal fluorescence images of cells and a pixel intensity map is obtained. Each pixel value is attributed to the refractive index of the imaged specimen, and a virtual optical lattice is constructed that represents the 2D profile of the refractive index variations. Two samples with different refractive index distributions would have optical lattices with different structural disorders and thus have different IPR values. A method based on such a light localization analysis to quantify the refractive index fluctuations in a biological material is applied to study the refractive index variations of DNA molecules in cancerous cells, thereby enabling the differentiation of malignant cells from the normal ones. This technique may have its potential in finding out disorder at the cellular level in biological studies and characterization of structural disorder in soft optical materials.
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