Confined blue iridescence by a diffracting microstructure: an optical investigation of the Cynandra opis butterfly

When illuminated and viewed along certain well-defined directions, segments on the wings of the butterfly Cynandra opis shows a striking violet-blue t o blue-green. We quantify the spectral and the directional properties of th ese areas of the wings of the insect. Electron microscopy shows that wing s cales from these iridescent regions of the wings contain two gratinglike mi crostructures crossed at right angles. Application of the diffraction theor y, as formulated by the Stratton-Silver-Chu integral, to the microstructure can explain all the important features observed experimentally. (C) 1999 O ptical Society of America. OCIS codes: 240.6490, 170.1420, 050.1940.