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  • 學位論文

金奈米球的非線性散射強度調節之機制

The mechanisms of amplitudinal modulation of nonlinear scattering in gold nanospheres

指導教授 : 朱士維
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摘要


貴金屬奈米粒子的非線性在過去數十年當中已被廣泛地研究。由貴金屬形成的電漿子奈米粒子可以藉由它們高載子密度與獨特的價帶結構,來提升金屬中的非線性。這些奈米粒子的非線性有兩個重要應用:在生物成像中作為非線性標記,以及全光學信號控制 。最近,我們發現一種新的非線性現象,那就是當金奈米粒子受到連續波雷射激發時,會產生非線性散射。一般來說,散射是線性的,即入射光強度與散射光強度成正比。而我們發現,當金奈米粒子受到激發時,散射並不會隨著入射增加,顯示出非常強的非線性。在高激發強度下(MW/cm2),散射會偏離至線性趨勢以下,若繼續提高激發強度,散射反而會超過線性趨勢。我們把前者命名為「飽和散射」,後者則命名為「反飽和散射」。這新穎的非線性首先被利用在超解析顯微術,可以使電漿子奈米結構的解析度提高至八分之一波長,而在最近,被利用於全光學開關,可以使信號被關閉80%。間接證據顯示熱晶格是「飽和散射」的主要機制,但是,信號的關閉深度、與「反飽和散射」皆無法被已知的古典模型所預估。在本篇論文裡,我們首先透過實驗驗證熱晶格主張,接著透過米氏理論,並使用溫度相關的介電系數計算孤立奈米粒子的散射光譜。我們先示範信號的非線性無法被已知的古典模型推估,並從馬克斯威-賈內理論得到提示:奈米粒子與塊材應具有不同的介電系數。於是我們修正了羅倫茲-德魯模型,加上了代表局部表面電漿振動的振子。出乎意料地,該振子的羅倫茲-德魯參數揭露了熱晶格如何參與非線性散射。這模型能夠精確描述「飽和散射」,也暗示了「反飽和散射」應該是仰賴其他的機制。

並列摘要


Nonlinearity in noble metallic nanoparticles has been studied extensively for decades. Plasmonic nanoparticles made of noble metals enhances the nonlinearity due to their high carrier density and unique band structures. Two important applications are nonlinear labels in bio-imaging, and all-optical signal manipulations. Recently, we discovered a new nonlinear phenomenon on the scattering of gold particles when excited by continuous-wave (CW) lasers. Conventionally, scattering should be linear, i.e. proportional to the incident intensity. We found that when the excitation intensity in gold nanospheres increases, the scattering may not increase accordingly, showing significant nonlinear response. At high intensity (MW/cm2), the scattering is below the linear trend, and if the intensity further increases, the scattering surpasses the linear trend. We describe the former as “saturable scattering” and the latter as “reverse saturable scattering.” The novel nonlinearity has been first applied to super-resolution microscopy with spatial resolution of plasmonic nanostructures down to λ/8, and recently used in ultrasmall all-optical switching with up to 80% modulation depth. The mechanism of saturable scattering has been proposed with indirect evidence: hot lattice is the major mechanism. Nevertheless, the modulation in scattering amplitude cannot be calculated through known classical models, and the mechanism for reverse saturable scattering is still unknown. In this work, we first confirm the proposition for hot lattice with experiments, then calculate the single-particle scattering spectrum with temperature-dependent permittivity by Mie theory. We compare the calculation to experiments to show the nonlinearity cannot be obtained through known classical models, then derive hints from Maxwell-Garnett theory. From the hints, we propose that nanoparticles having different permittivity to that of the bulk material. Thus, we correct the Lorentz-Drude model with an oscillator representing the localized surface plasmon. Surprisingly, the Lorentz-Drude parameters of such oscillator unveil how hot lattice participate in nonlinear scattering. The model provides accurate description for saturable scattering. It also implies the reverse saturable scattering should rely on other mechanisms.

參考文獻


25. S.-W. Chu, H.-Y. Wu, Y.-T. Huang, T.-Y. Su, H. Lee, Y. Yonemaru, M. Yamanaka, R. Oketani, S. Kawata, S. Shoji, and K. Fujita, "Saturation and reverse saturation of scattering in a single plasmonic nanoparticle," ACS Photonics 1, 32-37 (2014).
28. Y.-T. Huang, "Mechanism of Nolinear Scattering of Single Gold Nanosphere," in Department of Physics(National Taiwan University, Taiwan, 2014).
1. D. Pines, and D. Bohm, "A collective description of electron interactions: II. collective vs individual particle aspects of the interactions," Phys. Rev. 85, 338-353 (1952).
2. W. Nie, "Optical nonlinearity: phenomena, applications, and materials," Adv. Mater. 5, 520-545 (1993).
4. Y. Chen, and H. Ming, "Review of surface plasmon resonance and localized surface plasmon resonance sensor," Photonic Sensors 2, 37-49 (2012).

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