While surface microstructures of butterfly wings have been extensively studied for their structural coloration or optical properties within the visible spectrum, their properties in infrared wavelengths with potential ties to thermoregulation are relatively unknown. The midinfrared wavelengths of 7.5 to 14 µm are particularly important for radiative heat transfer in the ambient environment, because of the overlap with the atmospheric transmission window. For instance, a high midinfrared emissivity can facilitate surface cooling, whereas a low midinfrared emissivity can minimize heat loss to surroundings. Here we find that the midinfrared emissivity of butterfly wings from warmer climates such as Archaeoprepona demophoon (Oaxaca, Mexico) and Heliconius sara (Pichincha, Ecuador) is up to 2 times higher than that of butterfly wings from cooler climates such as Celastrina echo (Colorado) and Limenitis arthemis (Florida), using Fourier-transform infrared (FTIR) spectroscopy and infrared thermography. Our optical computations using a unit cell approach reproduce the spectroscopy data and explain how periodic microstructures play a critical role in the midinfrared. The emissivity spectrum governs the temperature of butterfly wings, and we demonstrate that C. echo wings heat up to 8 °C more than A. demophoon wings under the same sunlight in the clear sky of Irvine, CA. Furthermore, our thermal computations show that butterfly wings in their respective habitats can maintain a moderate temperature range through a balance of solar absorption and infrared emission. These findings suggest that the surface microstructures of butterfly wings potentially contribute to thermoregulation and provide an insight into butterflies' survival.

中文翻译：

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蝴蝶翅膀微结构的红外光学和热学特性。

虽然蝴蝶翅膀的表面微结构因其结构着色或可见光谱内的光学特性而被广泛研究，但它们在红外波长中的特性与体温调节的潜在联系相对未知。7.5 至 14 µm 的中红外波长对于周围环境中的辐射热传递尤为重要，因为它与大气传输窗口重叠。例如，高中红外发射率可以促进表面冷却，而低中红外发射率可以最大限度地减少对周围环境的热损失。在这里，我们发现来自温暖气候的蝴蝶翅膀的中红外发射率，如 Archaeoprepona demophoon（墨西哥瓦哈卡）和 Heliconius sara（Pichincha，使用傅里叶变换红外 (FTIR) 光谱和红外热像仪，厄瓜多尔）比来自 Celastrina echo（科罗拉多州）和 Limenitis arthemis（佛罗里达州）等较冷气候的蝴蝶翅膀高出 2 倍。我们使用晶胞方法的光学计算重现了光谱数据并解释了周期性微结构如何在中红外中发挥关键作用。发射率光谱控制着蝴蝶翅膀的温度，我们证明，在加利福尼亚州欧文市晴朗的天空中，在相同的阳光下，C. echo 翅膀比 A. demophoon 翅膀加热高达 8 °C。此外，我们的热计算表明，蝴蝶翅膀在各自栖息地中可以通过太阳能吸收和红外线发射的平衡保持适度的温度范围。