Abstract
A common problem of light sources emitting from an homogeneous high-refractive index medium into air is the loss of photons by total internal reflection. Bioluminescent organisms, as well as artificial devices, have to face this problem. It is expected that life, with its mechanisms for evolution, would have selected appropriate optical structures to get around this problem, at least partially. The morphology of the lantern of a specific firefly in the genus Photuris has been examined. The optical properties of the different parts of this lantern have been modelled, in order to determine their positive or adverse effect with regard to the global light extraction. We conclude that the most efficient pieces of the lantern structure are the misfit of the external scales (which produce abrupt roughness in air) and the lowering of the refractive index at the level of the cluster of photocytes, where the bioluminescent production takes place.
Highlights
Most living organisms - including ourselves - use light as a primary source of energy and as an information carrier for communication
We will carry out this work in five steps : (1) [section II] a reference system is first defined; (2) the results of morphology investigations is reported; (3) computer simulations of the optical behavior of each individual recognized substructural lantern element and conclusions on the positive or adverse effect on light extraction are presented; (4) a global model, that takes into account the set of relevant substructures, will be considered in order to provide some theoretical estimate of the external efficiency; (5) we show how these calculated estimates get support from direct observations
We will reconsider all the substructures revealed by the scanning electron microscopy analysis as described in the previous section and, on the basis of computer simulations, investigate the optical properties of each observed substructure separately in order to discuss their possible contribution to light extraction
Summary
Most living organisms - including ourselves - use light as a primary source of energy and as an information carrier for communication. Bioluminescent animals from the deep are usually emitting blue and get the help of symbiotic luminescent bacteria [1] to produce their light. Well understood is the way the bioluminescence can be switched on and off to produce flashes that, sometimes, can be short (pulse duration under a second) and undergo amazingly fast rises and falls Another problem – which has has been neglected up to now, except maybe for a preliminary report of part of the present work in a conference abstract [6] – is the optical origin of the external efficiency of the firefly lanterns. We will carry out this work in five steps : (1) [section II] a reference system is first defined; (2) the results of morphology investigations is reported; (3) computer simulations of the optical behavior of each individual recognized substructural lantern element and conclusions on the positive or adverse effect on light extraction are presented; (4) a global model, that takes into account the set of relevant substructures, will be considered in order to provide some theoretical estimate of the external efficiency; (5) we show how these calculated estimates get support from direct observations
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