I investigate the optical properties of guanine cytoplasm bi-layer stacks common in fish skins, with the goal of understanding how the structure of the stacks is important in producing a silvery reflectance. A simple model for the optics of a guanine cytoplasm multilayer stack is used to predict the reflectivity across visible wavelengths of light. A method, termed “f-value” deviates measure, is devised to quantify the similarity of the reflectivity spectrum to a perfect silver mirror reflectivity spectrum. A MATLAB optimization routine is used to identify local solutions of stack layer thicknesses which minimize the f-value measure. I find that the larger the number of layers in the stack the easier it is to devise a guanine cytoplasm bi-layer stack with a spectrum similar to silver mirror uniform reflectance. I note that stacks with constant layer thicknesses, such as equal layer and quarter-wave stacks, are poor uniform reflectors compared to chirped and random layer thickness stacks and conclude that variation in layer thicknesses is important for silvery reflectance.
Research report for a project during Complexity Sciences MRes/PhD programme, Faculty of Science, University of Bristol January 2009
supervisors: Professor Julian Partridge & Professor Noah Linden