Figure 7

Absorption coefficient of the pigment in the wings of Hetaerina americana and the resulting contribution to the refractive index. (a) The absorption coefficient spectrum derived from the absorbance spectrum of Figure 4b with a membrane thickness of 2.5 µm. The spectrum is decomposed into two components, an α band and a β band, which are assumed to follow modified lognormal functions (see the section on ‘Materials and methods’). (b) The difference between the refractive indices of the membranes in the red and clear wing parts derived from Figure 6c (expt) and the contributions to the refractive index from the components of the absorption coefficient spectrum (the α and β bands and their sum) calculated with the Kramers–Kronig dispersion relation (Equation (8)).