基於表面等離子體的納米器件已經在近幾十年引起了十分廣泛的興趣因為其對於半波長光子器件，光學傳感，光譜學以及光學捕獲有著廣大的應用前景。表面等離子體是一種被限定於金屬和介質介面上的一種光子-電子混合模式，而且它具有許多吸引人的特質，比如對金屬表面周圍環境極其敏感，納米尺度範圍的光學電磁場局域和場增強，以及對鄰近物體極強的場強梯度捕獲力。雖然這些特性都已經分別被廣泛的研究過，但從光學捕獲的角度去實現光學傳感的方案並還沒有引起大量的關注。很明顯，在納米尺度範圍內操縱目標的可能性將使得新的納米器件具有高的光學探測性能和多功能性。為了涉及這個論題，本項目包括新穎的等離子體納米器件的研究，這些納米器件將能夠提供獨特的功能，在光學傳感，表面增強拉曼散射，以及光學捕獲方面。 / 在第一部分設計中，構建了一種基於雙層金屬納米條陣列的耦合系統。這樣的系統具有簡單的結構，易於加工和集成於微流系統的優點。由於這個系統內的光場耦合，場強可以進一步的被加強，這樣的特點有助於提高系統的敏感特性，尤其是通過強的光場來捕獲一些金屬的納米顆粒後。這個系統的光學共振條件可以從理論上進行模式分析得到。然後二維時域有限差分法證實了理論的分析而且進一步證明了利用該系統於光學傳感和捕獲的可能性。結果表明此系統的光學敏感度約為200nm/RIU，通過光學捕獲的金屬納米顆粒引起的近場調製和場增強可以使得表面增強拉曼散射的增強因數達到10⁹ 到10¹° 的高度。 / 在第二部分的設計裡，金納米環結構被證實了可以成為一個強大的工具作為表面等離子體納米光鑷來抓獲金屬納米顆粒。首先，金屬納米環具有很多優點比如對入射光的偏振不敏感，很寬的可調的共振範圍，有環的內腔周圍和內部有著均勻的光學場增強，以及很容易製備。這裡的設計著重于納米環在入射波長為785nm 的新穎的光學捕獲特性以及表面增強拉曼散射的性能。三維的時域有限差分法被用來計算結構的光學回應，以及麥克斯韋應力張量法被用來計算光學受力分佈情況。計算結果表明對於一個有20nm 大小的金納米顆粒球，納米環結構有最大的光學捕獲勢阱約32 KgT 。由於納米環結構周圍存在多個捕獲勢阱，使得其對目標捕獲顆粒具有約10⁶nm³ 的非常之大的有效體積。而且，被捕獲的顆粒會進一步的導致一些納米間隙的形成，這些納米間隙又會使得近場增強達到約160 倍的高度，這使得在實際應用中10⁸ 的表面增強拉曼散射的增強因數成為可能。 / 在第三部分的設計裡，全光納米操縱的概念被提出並證實，因為這樣的概念拓展了等離子體光鑷的一個極其重要的功能，那就是被捕獲的分子可以在捕獲和區域內被任意的操縱和轉移，而且這個區域是納米尺度的。設計的系統由梯度形金屬納米盤組成，這些納米盤具有不同的直徑，這使得它們支援不同波長的表面等離子體共振。通過改變入射光的波長和旋轉入射光的偏振態，就可以將捕獲的目標從一個納米盤轉移到另一個納米盤。三維的時域有限差分法和麥克斯韋應力張量法被用來證實了所提出的觀點。計算結果表明被捕獲的目標感受到的捕獲勢阱深度高達5000kgT/W/μm²，最大的光學轉矩約為336pN·nm/W/μm²，而且總的有效捕獲體積可達到10⁶nm³ 。在這部分的結尾，討論了所設計的系統在光學傳感方面潛在的應用前景。 / 在最後的部分裡，展示了一個實驗的證明來說明等離子體納米光鑷對目標捕獲的觀測問題，因為這樣的觀測對往後近期的相關實驗來說是首先要關心的問題。雖然兩種途徑已經在別處被證實了，分別是通過觀測系統的透射光的強度變化和系統共振波長的改變，來監測表面等離子體納米光鑷近場捕獲行為的發生，但是在這個部分裡，等離子體納米光鑷和表面增強拉曼傳感技術被結合在了一起並且被證實了這是另一種有效的方法用於觀測捕獲行為的發生。在本實驗中兩束鐳射光束被為別用來激發等離子體納米光鑷和表面增強拉曼信號，一束是633nm 的鐳射，另一束是785nm 的鐳射。表面等離子體納米光鑷簡單地由熱蒸鍍並熱退光的金顆粒納米島墊底構成，這個墊底的共振峰被調製到緊靠633nm 的位置。目標顆粒是由光化學生長合成的銀納米十面體，這些十面體被綁定了4-巰基苯甲酸分子的單分子層，且具有遠離633nm 和785nm 的共振峰。由於當等離子體納米光鑷被激勵的時候目標顆粒會被捕獲到近場的熱點內，這時近場的光場就會被極大的增強，所以表面增強拉曼的信號就會出現。這個過程也被用數值模擬的方法（三維時域有限差分法和麥克斯韋應力張量法）闡明了。更進一步的，當等離子體納米光鑷不被激勵的時候，被捕獲的目標顆粒可以被釋放掉，那樣表面增強拉曼的信號就會消失掉。所以，本設計不僅提供了一種強有力的探測等離子體光鑷捕獲行為的方法，而且能夠成為一種在生物探測方面可重複利用的“捕獲并傳感“的平臺。 / Surface plasmons (SPs) based nanodevices have attracted much research interest in recent decades due to their powerful application potentials for subwavelength optical circuits, optical sensing, spectroscopy, and optical trapping. SPs are the hybrid photon-electron modes bound at the interface of conductors and transparent materials, and they have lots of attractive properties such as sensitive to the changes of environment around the interface, strong optical field localization and enhancement in nanoscale domain, and strong field intensity gradient forces to trap the adjacent objects. Even though these properties have been widely investigated, their application in optical sensing based on the plasmonic optical trapping strategy remains largely unexplored. Clearly, the possibility of manipulating objects within the nanometer regime will enable new nanodevices that offer high optical detection performance and multiple-functionality. With the aim to address this issue, this project involves the study of novel plasmonic nanodevices that provide unique functionality in optical sensing, surface-enhanced Raman scattering (SERS), and optical trapping. / The first design is based on a coupling system involving double-layered metal nano-strips arrays. This system has the advantages of simple geometry and direct integration with microfluidic chips. The intense optical localization due to field coupling within the system can enhance detection sensitivity of target molecules, especially by virtue of the optical trapping of plasmonic nanoparticles. The optical resonant condition is obtained theoretically through analyzing the SPs modes. Numerical modeling based on two-dimensional (2D) finite-difference time-domain (FDTD) is consistent with the theoretical analysis and demonstrates the feasibility of using this system for optical sensing and trapping. Simulation results show that the refractive index sensitivity can reach ~200 nm/RIU, and a maximum SERS enhancement factor (EF) of 10⁹-10¹° is possible because of the near-field modulation and enhancement from optically trapped metal nanoparticles. / In the second design, a gold nano-ring structure is demonstrated to be an effective approach for plasmonic nano-optical tweezers (PNOTs) for trapping metallic nanoparticles. The plasmonic nano-ring structure has many interesting merits such as polarization insensitivity, wide tunable resonance range, uniform field enhancement around and inside the ring cavity, and ease of fabrication. This design has a unique feature of having large active volume for trapping. In our demonstration example, we have optimized a device for SERS operation at the wavelength of 785 nm. Three-dimensional (3D) FDTD techniques have been employed to calculate the optical response, and the optical force distribution have been derived using the Maxwell stress tensor (MST) method. Simulation results indicate that the nano-ring produces a maximum trapping potential well of ~32 kgT on a 20 nm gold nanoparticle. The existence of multiple potential well results in a very large active trapping volume of ~10⁶ nm³ for the target particles. Furthermore, the trapped gold nanoparticles further lead to the formation of nano-gaps that offer a near-field enhancement of ~160 times, resulting in an achievable EF of 10⁸ for SERS. / In the third design, we propose a concept of all-optical nano-manipulation. We show that target molecules, after being trapped, can be transferred between the trapping sites within a linear array of PNOTs. The system consists of an array of graded plasmonic nano-disks (NDs) with individual elements coded with different resonant wavelengths according to their dimensions. Thus, by switching the wavelength and rotating the polarization of the excitation source, the target nanoparticles trapped by the device can be manipulated from one ND to another. 3D FDTD simulation and MST calculation are utilized to demonstrate the operation of this idea. Our results reveal that the target experiences a trapping potential strength as high as 5000 kgT/W/μm², maximum optical torque of ~336 pN·nm/W/μm², and the total active volume may reach ~10⁶ nm³. The potential applications in terms of optical sensing are also discussed. / In the final design, for which experimental demonstration has been conducted, we show that PNOTs are achievable with random plasmonic nano-islands. Operation of the random PNOTs can be monitored by measuring the SERS enhancement factor in real time. Two laser beams having wavelengths of 633 nm and 785 nm are utilized to stimulate the PNOTs and excite the Raman signals simultaneously. The PNOTs are formed by annealing of a thermal evaporated gold film. This so-called nano-island substrate (Au-NIS) has a resonant peak close to 633 nm. The target is photochemical synthesized silver nanodecadedrons (AgNDs) functionalized with 4-Mercaptobenzoic acid (4-MBA) and the resonant peak of these AgNDs is far away from 633 nm and 785 nm. As the target is trapped to the hot-spots when the PNOTs are active, the near-field intensity is enhanced significantly, which results in the emergence of SERS signals, i.e. confirming the expected outcome of SERS upon nanotrapping by the PNOTs. This process is also elucidated numerically through 3D FDTD simulation and MST calculation. Furthermore, the target can be released as the PNOTs become inactive, i.e. disappearance of the SERS signal. Therefore, this design offers not only a robust avenue for monitoring trapping events in PNOTs, but also a reproducible “trap-and-sense“ platform for bio-detection. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Kang, Zhiwen. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 146-170). / Abstracts also in Chinese. / Abstract --- p.I / Acknowledgements --- p.VIII / List of Illustrations --- p.XIII / Chapter Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Surface Plasmon Polaritons and Localized Surface Plasmons --- p.1 / Chapter 1.2 --- Relevant Applications Based on Surface Plasmons --- p.3 / Chapter 1.3 --- Plasmonic Nano-Optical Tweezers and Relevant Applications --- p.7 / Chapter 1.4 --- Literatures Review and Objectives of this Thesis --- p.12 / Chapter 1.5 --- Structure of this Thesis --- p.17 / Chapter Chapter 2. --- Research Methodologies --- p.20 / Chapter 2.1 --- Theoretical Background of Surface Plasmons --- p.20 / Chapter 2.2 --- Numerical Simulation Techniques for Studying Complex Nanostructures --- p.30 / Chapter 2.3 --- Optical Force Calculation with the Maxwell Stress Tensor Method --- p.38 / Chapter 2.4 --- Nanostructure Fabrication and Characterization --- p.40 / Chapter Chapter 3. --- Optical Sensing Based on Double-Layered Metal Nano-Strips --- p.43 / Chapter 3.1 --- Introduction --- p.43 / Chapter 3.2 --- Theoretical Model and Analysis --- p.46 / Chapter 3.3 --- Numerical Verification and Discussion --- p.50 / Chapter 3.4 --- Optical Sensing Evaluation --- p.54 / Chapter 3.5 --- Near-Field Modulation by Optically Trapped Metal Nanoparticles --- p.58 / Chapter 3.6 --- Discussion --- p.61 / Chapter 3.7 --- Conclusion --- p.62 / Chapter Chapter 4. --- Gold Nano-Ring as Plasmonic Nano-Optical Tweezer --- p.64 / Chapter 4.1 --- Introduction --- p.64 / Chapter 4.2 --- Design and Optical Response --- p.67 / Chapter 4.3 --- Optical Force Calculation and Evaluation of Trapping Performance --- p.73 / Chapter 4.4 --- Stable Trapping Sites and Active Trapping Volume --- p.76 / Chapter 4.5 --- Near-Field Variation and Discussion --- p.81 / Chapter 4.6 --- Conclusion --- p.84 / Chapter Chapter 5. --- Graded Plasmonic Nano-Disks for Near-Field Nano-Manipulation --- p.86 / Chapter 5.1 --- Introduction --- p.86 / Chapter 5.2 --- Modeling and Optical Response --- p.89 / Chapter 5.3 --- Optical Force Distribution in the Structure --- p.91 / Chapter 5.4 --- Optical Trapping Potential and Rotational Energy --- p.96 / Chapter 5.5 --- Optical Trapping Volume and Discussion --- p.101 / Chapter 5.6 --- Conclusion --- p.104 / Chapter Chapter 6. --- Monitoring Plasmonic Nano-Optical Trapping through Detection of Surface-Enhanced Raman Scattering --- p.106 / Chapter 6.1 --- Introduction --- p.106 / Chapter 6.2 --- Numerical Investigation --- p.110 / Chapter 6.3 --- Sample Preparation and Characterization --- p.112 / Chapter 6.4 --- Experimental Implementation and Results --- p.122 / Chapter 6.5 --- Discussion --- p.134 / Chapter 6.6 --- Conclusion --- p.137 / Chapter Chapter 7. --- Conclusion and Outlook --- p.139 / References --- p.146 / Publications from this Work --- p.171

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Optical testing often requires a measurement of the phase difference between light from two different optical systems. One system is a master or reference system, and the other is a sample or test system. In the optical shop, the reference may be a precision optical surface and the test system may be a newly fabricated surface. A computer generated hologram is a geometric pattern that can be used as a precise reference in an optical test. Computer-generated holograms can be used to make reference systems that would be very difficult to make by other methods. Various encoding methods for making computer-generated holograms are discussed, and a new method is presented that can easily be used on image recorders intended for image processing applications. This general encoding method has many characteristics in common with earlier computer-generated holograms. Examples are given to demonstrate the properties of synthetic holograms and the differences among different encoding techniques. Geometric ray tracing is an essential part of the process of developing holograms for optical systems. A computer ray-trace code was developed to model the optical performance of equipment used in optical testing. This program was used to obtain numeric coefficients that describe the optical properties (optical path) needed to define a reference wavefront. A review of interferometer design leads to a discussion of how the hologram functions as a part of the interferometer and of the limitations to the computer-generated hologram. The diffraction pattern from the hologram, observed in the focal plane of a lens, is the key to understanding the use and limitations of the hologram in an interferometer. A detailed prescription is given for making a computer-generated hologram for a commercial interferometer designed for use with holograms. Problems of finding the proper focal point, the correct hologram size, and preparation of the final hologram image are discussed. An example of an actual test is included. Finally, an analysis of various errors encountered and the limitations of the methods used is presented. Within these limitations, computer-generated holograms can easily and routinely be used to test aspheric optical components.