奈米電漿子結構之近場光學研究與濾波微距透鏡技術之開發

Abstract

近年來，奈米電漿子學的結構與材料因其嶄新的物理效應而日益受到重視，其特性探討的最有力工具莫過於具備高空間解析度的近場光學顯微鏡，因此我們發展了適合此類樣品研究用的多功能近場光學量測設備與分析技術。在實驗上，我們製作了多孔隙金膜做為技術能量的驗證，並同時進行了該材料相關之物理研究。多孔隙金膜為利用去合金的方法製作而成，其具有20至350 nm尺寸的隨機孔洞分布於金膜表面，其遠場吸收光譜提供了該結構於635nm時具有表面電漿子共振效應的證據。我們利用近場光學的探針照明模式，發現了偽像現象來自於探針縱軸移動時的光學擾動，亦證實該偽像只在離軸量測時發生，而在同軸量測時則無此問題，因此提出了一個數學近似的方法來去除偽像；表面電漿子因金孔隙結構而產生的不同行為亦被探討，我們同時使用不同波長的光源來進行激發，確認了電漿子效應與波長相關的特性及其對純粹光學檢測上的影響；不同偏振的入射光源亦被實行，我們可藉由表面電漿子與偏振相關的物理特性，來定義出這類樣品在不同區域處的表面電漿子行為和結構之間的關係。本論文同時亦提供了對於幾種式樣的表面電漿子樣品完整的量測與研究方法。 此外，我們亦發展了一種新穎之光學微距濾片透鏡技術，可有效克服在有限共軛的微距光學系統中，吸收型濾片材料所造成的光譜像差問題。其技術包含兩項鏡片的組成，一為濾片透鏡，二為特寫透鏡。濾片透鏡的功能為取代傳統之光學濾片，以其鏡片結構來補償非準直光束於進入介質後的路程，進而消除光程差之存在。特寫透鏡的功能則為提供微距攝影之能力，其裝設於一般數位相機鏡頭與被測物之間，且針對微距透鏡行以光學優化，準直將進入鏡頭內的發散光源。此光學微距濾片透鏡技術針對微距光學之成像目的，非但能提供影像更加良好的光譜均勻度、均一的光強資訊，並且更有低成本、輕巧、易於裝置使用於各式相機鏡頭的便利性與相容性。此研究乃僅為一典型範例，其概念可擴充至所有種類之濾片應用，包含色鏡片、偏振片、玻片等等。是以對於未來精度要求極高之各式先進光學量測，必能供予十足的技術支持

Near field scanning optical microscopy (NSOM) is a powerful tool because of its high spatial resolution and has been widely used in nano-photonics, such as super-resolution optics, surface-enhanced Raman scattering, metamaterials and plasmonics. For this reason, we setup a multifunction NSOM for measuring different types of plasmonic nanostructures. Topographic artifacts and surface plasmon influences on the near-field optical images of a porous Au film are observed experimentally. Under tip illumination, topographic artifacts are found to be present in a reflection mode optical image but not in a transmission mode image. A simple algorithm is used for filtering the topographic artifacts and extracting a correct near-field optical image approximately. Surface plasmon influences are present in both modes. By using three exciting wavelengths of 488, 647.1, and 520.8 nm, it is confirmed that a suitable wavelength should be chosen for avoiding the surface plasmon interference in a near-field optical investigation of morphological or material dielectric contrast. Plasmonic or non-plasmonic regions on the porous Au film can be identified from the observed optical intensity variation in the optical images obtained at incident polarizations of 0°, 90°, and 45°. In addition to the porous Au film, we study the elliptical nanohole ensembles, super resolution cover glass slip and specific plasmonic structures/particles in this doctoral dissertation. On the other hand, a filtering macro-lens was developed to simultaneously achieve macro-optical imaging and correct spectrum aberration. The macro-lens was a doublet lens composed of a filtering lens and a close-up lens. The shape of the filtering lens was designed to eliminate the optical path differences between the light rays in the absorbing medium. The close-up lens was designed to decrease the effective focal length of an ordinary camera lens to provide high magnification capability and collimate the diverging beams through the filtering lens. Experimental results demonstrated that the spectrum uniformity of the macro-optical images was markedly improved by the filtering macro-lens. This innovation may be used in finite conjugate optical systems and has great potential for various filter application.