Coherent light emission from teleost iridophores

Iridescence is observed in both plants and animals. The iridescent color of fish iridophores is caused by guanine platelets separated by layers of cytoplasm, where the color depends on several factors including the size, shape, orientation, and ordering of the guanine platelets found in iridophores. Many silvery fish use their iridophores with aperiodic photonic structures as camouflage, while other species of fish have developed periodic photonic crystal structures for communication. Some passive, linear, optical techniques have been developed to investigate the visual appearance of animals with structural color including spectrophotometry, coherent back scatter, imaging scatterometry, determination of total reflected light with an integrating sphere, and methods that study the photonic structures after changing the refractive index of the fluid/void region. A sensitive nonlinear method to quantify the aperiodic photonic structures in silvery fish iridophores is presented, where the amplified spontaneous emission threshold is used to determine a single figure-of-merit. Preliminary observations of one-dimensional, distributed-feedback, laser emission from periodic photonic crystal structures found in the iridophores of a freshwater fish will also be presented.