  The birdwings butterfly Troides magellanus possesses interesting properties
for light and thermal radiation management. The black wings of the male exhibit
strong (98%) absorption of visible light as well as two strong absorption peaks
in the infrared both due to chitin. These peaks are located in the spectral
region where the black body emits at 313K. The study of absorption enhancement
in this butterfly could be helpful to design highly absorbent biomimetic
materials. Observations of the wings using a scanning electron microscope (SEM)
reveal that the scales covering the wings are deeply nanostructured. A periodic
three-dimensional (3D) model of the scale nanoarchitecture is elaborated and
used for numerical transfer-matrix simulations of the absorption spectrum. The
complex refractive index of the wing material is approximated by a
multi-oscillator Lorentz model, leading to a broad absorption in the visible
range as well as two peaks in the infrared. The absorption peak intensities
turn out to be dependent on the complexity of the nanostructures. This result
clearly demonstrates a structural effect on the absorption. Finally, a
comparison with a planar layer of identical refractive index and material
volume lead us to conclude that the absorption is enhanced by nanostructures.
