探討永久電雙極對材料之影響

On the Influence of Permanent Electric Dipoles on Optical/Photonic Materials

蔡博宇(Po-Yu Tsai)

指導教授 ： 廖重賓

共同指導教授 ： 郭文凱(Wen-Kai Kuo)

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2010年)

https://doi.org/10.6827/NFU.2010.00109

摘要

當一光波（電磁波）入射至一材料時，材料界面上的光學現象（含反射、折射、透射），傳統上，都是由古典光學的Fresnel’s Equations加以描述。然而，這些巨觀的光學現象背後真正的微觀（microscopic）物理成因，其實是光子（photon）被電/磁雙極（electric/magnetic dipoles）散射（scattering）之集總結果。其中，電/磁雙極的角色即為微觀電磁波散射之源頭（亦即，微小的發射天線）。
本研究在此觀點下，藉由推導Fresnel’s Equations 散射型式之過程中知道電/磁雙極進入此巨觀之公式，因而進一步了解加入永久電雙極（permanent electric dipoles）如何可以改變一材料之布魯斯特角（Brewster angle），包含其與入射光波之功率（更準確地說，入射光之電場強度）、永久電雙極方向角之相關性，以及兩共軛入射路徑間之折射不對稱現象。然後，利用此所謂的“電雙極工程（dipole engineering）”，增減一有機高分子薄膜（Polyvinylidene Fluoride，PVDF）內部之永久電雙極，再於可見光頻率下，進行布魯斯特角實驗，證實上述理論之預測。隨後，由實驗結果定量算出PVDF內部對可見光頻率有反應的永久電雙極之等效極化密度（polarization density）與其方向角。接著，並據此繪出當入射角為大角度時，具對稱開岔（open splittings）之原本為3維折射率橢球切面（refractive index ellipse）圖。最後，再指出永久電雙極（如：奈米粒子）之存在對傳統表面電漿共振（surface plasmon resonance, SPR）類之量測可能產生的可觀影響。
此研究計畫係在國立虎尾科技大學光電同調控制實驗室與奧博實驗室之全力支援下進行。

關鍵字

電雙極工程 ； 永久電雙極 ； 布魯斯特角

並列摘要

In arriving at the more intuitive “scattering form” of the Fresnel equations, microscopic physical electric and magnetic dipoles were rigorously employed as the sources of EM waves by Doyle et al. Motivated by such an approach, the authors started to speculate how the incorporation of permanent dipoles might affect the Brewster angle of a specific optical material. It is found that in the presence of permanent dipoles, not only is the Brewster angle dependent on the incident light power as well as the dipole orientation, but also that two conjugate incident light paths result in distinctively different refractions.
Experiments on dipole-engineered PVDF (polyvinylkidene fluoride) films show that by way of adding/reducing permanent dipole density and varying orientations, the aforementioned theoretical predictions can be evidenced unambiguously in the visible light range. Further, new effective polarization density can be quantified from the above experiments subjected to different dipole engineering processes. As a result, the traditionally elliptic contour of a slanted section of the 3D refractive index ellipsoid now manifests symmetric open splittings at large incident angles. It implies that severe challenge to the accuracy of traditional surface plasmon resonance (SPR) measurements may arise in the presence of permanent dipoles of various morphologies, such as in the form of nano-particles.

並列關鍵字

dipole-engineered ； permanent electric dipoles ； Brewster angle

參考文獻

[1] J. C. Maxwell, “A Dynamical Theory of the Electromagnetic Field,” in Philosophical Transactions of the Royal Society of London, 155, p. 459 (1895).

[2] H. Hertz, “Ueber strahlen elektrischer kraft,” Ann. Phys. Chem. Leipzig., 36, pp. 769-783(1889).

[5] W. T. Doyle, “Scattering Approach to Fresnel’s Equations and Brewster’s Law,” Am J. Phys. 53, 463 (1985).

[6] ChungpinLiao et al.,“Manipulating the Brewster Angles by Using Microscopically Coherent Dipole Quanta and Its Possible Implications,” J. Lightwave Technol.24 No. 8, pp.3248-3254 (2006).

[9] K. M. Yassien et al., “On the digital holographic interferometry of fibrous material, I: Optical properties of polymer and optical fibers,” Opt. Lasers Eng.48, Issue 5, Pages 555-560 (2010).