奈米直寫儀用表面電漿光學元件之理論與實驗

Theory and Experiments of Plasmonic Optical Components for Nano Writer

林鼎晸(Ding-Zheng Lin)

指導教授 ： 李世光 ； 葉超雄

國立臺灣大學/工學院/應用力學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.00365

摘要

由於光學繞射極限的限制，聚焦光點受到入射光波長及透鏡數值孔鏡的影響。為了縮小光點，科學家們不斷研發各種技巧，例如使用浸潤式微影、環狀照明和選擇性記錄縱向電場等。然而昂貴的短波長光源及稀有的短波長光源透鏡材料卻不斷延遲的微影技術發展的腳步。
1998年，由於T. W. Ebbesen教授發現了異常穿透現象，使得表面電漿光學重新被喚起興趣。本論文使用表面電漿光學的原理來設計光學元件。文中提出了數種新穎的光學頭設計概念，包括金屬光學頭(MM)、單邊結構光學頭(AS)、介電值-金屬光學頭(DM)、多通道光學頭(MS)、次波長圓環光學頭等(SAA)……等。並逐一以實驗驗證其光學性質與可行性。
模擬方面提出了完整的模擬流程，包括利用嚴格耦合波理論快速估算出射光指向角或利用有限差分時域法計算出射光電磁場分佈。模擬結果與實驗有良好的一致性。這些模擬不僅可幫助我們用來預測未知的物理現象，更可以提供我們電漿子透鏡設計的相關參數。
實驗方面，我們使用倒立式顯微鏡觀測指向性出射的現象，並使用近場光學顯微鏡量測次波長圓環結構的近場及遠場特性。不但發現銀次波長圓環結構的近場具有表面電漿波干涉的條紋，更驚喜的發現其出射光具有高穿透能量、次波長聚光點、及長焦深等特性。這些獨特的光學特性使得電漿子透鏡成為透鏡微小化的最佳選擇之一。
簡言之，表面電漿提供了一個在微小世界操控光路的可能性，於今日奈米科技蓬勃發展之際，有潛力與其他學術及工程領域相結合，激盪出新的研究火花。

關鍵字

表面電漿 ； 奈米光學 ； 光學頭 ； 貝索光束 ； 指向性出射 ； 近場光學

並列摘要

Due to optical diffraction limits, the focal spot size is influenced by the incident wavelength and the numerical aperture of a lens. In order to shrink the size of the focal spot, scientists continuously develop all kinds of techniques, which include immersion lithography, annular illumination, and selectively recording the longitudinal field (Ez), and so on. However, the high cost of light source and the rarity of lens material at shorter wavelength obstruct the development of lithography techniques.
In 1998, Professor T. W. Ebbesen discovered the extraordinary transmission and re-triggered the worldwide research interests on plasmonic optics. In this thesis, we used the theory of plasmonic optics to design new optical components. We proposed many concepts to design a novel optical head, including metal surface grating on metal (MM structure), dielectric surface grating on metal (DM structure), multi-slits structure (MS structure), subwavelength annular aperture structure (SAA structure)......etc. We also performed experiments to verify the optical properties and feasibilities of optical head continuously.
In the section of simulations, we proposed a complete simulation process, including easy estimation on the beaming angle of emitted light by using Rigorous Coupled Wave Analysis (RCWA) method, using Finite-Difference Time-Domain (FDTD) method to calculate the electric field distribution, etc. The simulation results agree well with our experiments. These simulations not only can help us predict the unknown phenomena but also provide us with the related parameters needed to design a plasmonic lens.
In the section of experiments, we used inverted microscope to observe directional beaming phenomena, and used near-field scanning optical microscope (NSOM) to measure the near-field and far-field optical properties of a subwavelength annular aperture (SAA). We not only found the interference fringe of surface plasmon existed at near-filed of the silver SAA structure, but surprisingly discovered the emitting light through the silver SAA structure has characteristics of high transmission energy, subwavelength focal spot, and long depth of focus. These unique optical properties make plasmonic lens one of the best choices for miniature lens.
In short, the surface plasmon offers a possibility to manipulate light in microscopic world and provides us with a potential to create new research fields at the age of nanotechnology.

並列關鍵字

surface plasmon ； nano optics ； optical head ； Bessel beam ； directional beaming ； NSOM

參考文獻

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