Light Scattering Enhancement at the Absorption Edge in Dewetting Droplets of Cyanine Dyes

Diffraction properties of thin films of dewetted cyanine dye droplets are investigated and related to the complex refractive index. Strong changes in the index of refraction are often found near the absorption edge of organic dyes. Within a small window of droplet morphologies, scattering efficiency is maximized and becomes wavelength-selective. The origin of the high scattering efficiency is found to be in the enhancement of scattering at the absorption edge of the dye, where anomalous refractive index dispersion occurs. For a comprehensive understanding of the scattering effect, an analytical solution for the diffraction of an array of scatterers is presented. Finite-difference time-domain simulations of the extinction properties are performed and good agreements to the experiments are found. These results pave the way to an easy fabrication of new organic-based optical devices such as refractive index-based sensors or color selective diffraction gratings.