Abstract

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.

A. Malins
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
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