NANO-SIZED PERIODIC STRUCTURES IN CUTICULE OF INSECTS AND THEIR OPTICAL FUNCTIONS

这个项目的目的是研究在某些昆虫的角质层上形成的纳米结构的光学功能。我们将注意力集中在角质层精细结构中的周期结构上，并提出周期结构是产生其光学功能的主导结构。我们研究了南美雄性Morpho和日本雄性Lycaenidae两种蝴蝶的翼鳞和角膜。在项目方面，我们进行了以下研究：(A)利用扫描电子显微镜观察了蝴蝶的鳞片，研究了结构有色翅膀的微观构筑。结果发现，翼鳞被认为是由片层和脊状结构组成的周期性结构。接下来，我们观察到，蝴蝶的小眼角前表面覆盖着微小的乳头，远小于可见的右侧波长，并以六角阵列排列。需要注意的是，角膜可以看作是乳头阵列的二维周期结构。(B)我们用直径约100微米的显微光谱仪测量了翼鳞的光谱反射率。实验结果表明，每个鳞片都呈现出明亮的蓝色或绿色。角膜突起阵列的光学功能可能是减少可见光从角膜前表面的反射[C.G.Bernhard，Endeavour，26，79-84(1967)]。(C)我们开发了一个数值算法来分析与翼状鳞片或角膜的周期性结构相关的光学功能。该算法基于Yasuura方法，解决了一个大规模的最小二乘问题。我们通过计算机模拟评估了昆虫角质层中周期结构模型在可见光区域的反射率和透射率。

The aim of this project is to investigate optical functions of nano-sized structure that are formed on cuticles of certain insects. We focus our attention on periodic structures in the fine architecture on the cuticles and propose that the periodic structures are dominant to produce their optical functions. We deal with wing scales and ommateal corneas of two species of butterflies, male Morpho from South America and male Lycaenidae from Japan. In the term of project, we have carried on the following studies.(A)We have observed scales of the butterflies by using a scanning electron microscope to investigate microscopic architectures of structurally colored wings. As a result, we found that the wing scales are regarded as periodic structures that consist of lamella and ridge. We next observed that the front surface of ommateal corneas of the butterflies is covered with minute nipples, which is much smaller than a wavelength of visible right and arranged in hexagonal array. It should be noted that the corneas could be considered as two-dimensional periodic structures of the nipples array.(B)We have measured the spectral reflectance of wing scales by a microscopic spectrometer whose spot size is about 100 micrometer in diameter. The experimental results show that each scale exhibits brilliant blue or green. Optical functions of the corneal protuberance array might be to reduce the reflection of visible light from the front surface of cornea [C.G.Bernhard, Endeavour, 26, 79-84 (1967)].(C)We have developed a numerical algorithm for analyzing optical functions associated with periodic structures in wing scales or ommateal corneas. The algorithm, which is based on the Yasuura method, leads us to solve a huge-sized least squares problem. We evaluate reflectance and transmittance of the periodic structure models in cuticles of insects over the visible region from computer simulation.