壓克力(PMMA)菲涅爾鏡片於紅外線波段的設計與製作

Abstract

紅外線攝影像技術是藉由探測物體散發的紅外線來重建影像的技術，藉由此技術，我們可以在缺乏可見光的情況下偵測四周環境。然而，大部分用於製作普通鏡片的材料，例如玻璃，對紅外線都有很高的吸收率。以前常用於紅外線鏡片的材料，如矽、鍺也有著其缺點。其中一個重要的缺點是這兩種材料皆為堅硬且易脆，要用這兩種材料形成有弧度的彎曲鏡片通常必須透過鑽石研磨，因此紅外線鏡片的成本往往高於普通鏡片的成本。多年來，雖然不少廠商都有投入新材料的研發而且也有一些成果被發表，但是這些新材料的配方卻往往被視為商業機密而被開發廠商保護著，因此這些材料還是不能被大眾所知悉。 我們發現Poly(methyl methacrylate)(縮寫PMMA，俗稱壓克力)在中紅外線波段有著不錯的穿透率，同時又是一種極容易取得的材料。更重要的是，液態的PMMA可以輕易的被塑型成任何我們想要的形狀。因此，在這篇論文中，我們討論了一下PMMA在紅外線波段的光學特性，接著我們設計並模擬了利用PMMA製作的菲涅爾透鏡，我們設計出來的鏡片直徑10毫米，焦距14毫米，模擬的結果證實了我們的設計可以有效的聚焦紅外線。 最後，我們採用了一種新的製成方式製作我們的菲涅爾透鏡。跟傳統的製作方式相比，我們的製成不僅成本較低同時也更為簡單，十分適合工業上大規模生產。而製作完成的鏡片也利用了各種檢測去測量其結構和光學特性。測量結果顯示，利用我們的製成，我們可以成功的製作出符合我們設計的PMMA紅外線菲涅爾透鏡。

Infrared thermography is a promising solution that can help improve our lives. However, most of the common materials used to fabricate lenses are opaque in the infrared range. Silicon and germanium are better solutions. But shaping these two materials are truly complicated and time-consuming. Many companies have devoted themselves to develope new materials. Though some results have been published recently, the recipe of the new materails are still usually protected as the commercial secret. Due to material restriction, traditional lenses to focus infrared rays are ususally expensive. Poly(methyl methacrylate) is an ubiquitous polymor material. It is cheap and transparent in mid-IR range. More importantly, liquid PMMA can be shaped and solidified easily. Therefore, we chose PMMA as the material to design and make our IR lenses. In this research, we introduce a common material - Poly(methyl methacrylate) and discuss its optical properties in mid-IR range. We design a Fresnel lens with diameter 10 mm and f/1.4. We also run the simulation by using ZemaxR. The simulation results are the same as our design. We make the lens by our much low-cost and easier fabrication process. After that, we examine the structure and optical characteristic of our PMMA fresnel lens. The examine results also show that the lens is quite identical to our design.