TY - JOUR
T1 - Absence of circular polarisation in reflections of butterfly wing scales with chiral Gyroid structure
AU - Saba, Matthias
AU - Wilts, Bodo D.
AU - Hielscher, Johannes
AU - Schröder-Turk, Gerd E.
N1 - Publisher Copyright:
© 2014 The Authors.
PY - 2014
Y1 - 2014
N2 - The single Gyroid, a triply-periodic ordered chiral network of cubic symmetry, appears as a nanostructure in the green-colored wing scales of various butterflies. In lossless and perfectly ordered single Gyroid materials, the structural chirality leads to circularly polarized reflections from crystals oriented in the [100] direction. Here we report a circular polarisation study of the macroscopic reflections of the wing scales of Callophrys rubi and Teinopalpus imperialis that reveals no circular dichroism, that is, we find no significant difference in the reflectance values for left- and right-circularly polarized light. The reasons for the absence of circularly polarized reflections is likely to be a compound effect of various factors, including crystallite orientation, presence of both leftand right-handed single Gyroid enantiomers, and structural disorder. Each of these factors weakens, but does not fully extinguish, the circular polarisation signal. We further find a substantial amount of blue-absorbing pigment in those wing scales of C. rubi that are structured according to the single Gyroid. Numerical simulations demonstrate that absorption, while evidently reducing overall reflectance, does generally not reduce the circular dichroism strength. The experimental findings of this paper, however, clearly demonstrate that circular dichroism is absent from the reflections of the butterfly wing scale. Henceforth, the chiro-optical response of the idealised structure does not fulfil a biological photonic function.
AB - The single Gyroid, a triply-periodic ordered chiral network of cubic symmetry, appears as a nanostructure in the green-colored wing scales of various butterflies. In lossless and perfectly ordered single Gyroid materials, the structural chirality leads to circularly polarized reflections from crystals oriented in the [100] direction. Here we report a circular polarisation study of the macroscopic reflections of the wing scales of Callophrys rubi and Teinopalpus imperialis that reveals no circular dichroism, that is, we find no significant difference in the reflectance values for left- and right-circularly polarized light. The reasons for the absence of circularly polarized reflections is likely to be a compound effect of various factors, including crystallite orientation, presence of both leftand right-handed single Gyroid enantiomers, and structural disorder. Each of these factors weakens, but does not fully extinguish, the circular polarisation signal. We further find a substantial amount of blue-absorbing pigment in those wing scales of C. rubi that are structured according to the single Gyroid. Numerical simulations demonstrate that absorption, while evidently reducing overall reflectance, does generally not reduce the circular dichroism strength. The experimental findings of this paper, however, clearly demonstrate that circular dichroism is absent from the reflections of the butterfly wing scale. Henceforth, the chiro-optical response of the idealised structure does not fulfil a biological photonic function.
KW - Absorption
KW - Biophotonic crystals
KW - Birefringence
KW - Butterfly wing scale
KW - Chirality
KW - Chitin
KW - Circular polarisation
KW - Gyroid
KW - Optical activity
KW - Pigmentation
KW - Structural color
UR - http://www.scopus.com/inward/record.url?scp=84922989925&partnerID=8YFLogxK
U2 - 10.1016/j.matpr.2014.09.023
DO - 10.1016/j.matpr.2014.09.023
M3 - Article
SN - 2214-7853
VL - 1
SP - 193
EP - 208
JO - Materials Today: Proceedings
JF - Materials Today: Proceedings
ER -