侷域性雙偏極化光外差干涉動態光散射量測系統之建立

Localized Dual-Polarization Differential Heterodyne Dynamic Light Scattering System

周立德(Li-Dek Chou)

指導教授 ： 闕志達

共同指導教授 ： 曹恆偉(Hen-Wai Tsao)

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01450

摘要

本篇論文的主旨在研發一種新的雙頻率雙極化外差干涉雷射都卜勒測速 (Laser Doppler velocimetry, LDV) 和動態雷射光散射(Dynamic light scattering, DLS)系統. 其特色主要藉由光束平移元件 (Beam displacer) 雙頻率偏極化雷射光束建構成雙軸雷射都卜勒測速系統和動態雷射光散射系統。兩系統之間的差異主要在於偵測散射光子信號強度的不同，前者屬於高強度散射光，而後者為弱散射光。本篇論文由理論的推導建立，至實驗中對精密旋轉馬達測速以及奈米粒子在溶液中的布朗運動和粒子大小的精密量測和分析，印證了本論文所提出方法的正確性。同時在本論文中亦對所提出方法和光學架構的特性以及優點，和傳統雷射都卜勒測速以及動態雷射光散射系統做詳細的比較和分析討論。本論文也對侷域的特性加以討論。

關鍵字

雙極化光 ； 外差干涉 ； 動態光散射 ； 雷射都卜勒 ； 侷域 ； 布朗運動

並列摘要

In this thesis, a novel and sensitive dynamic light scattering system for both laser Doppler measurements and observing in-plane Brownian dynamics of nanoparticles has been developed. The system is based on the interference of the direct back scattered portions of two incident orthogonally polarized beams striking the sample, observing the spectrum of the interference signal and analyzing its corresponding spectrum width and spectral shift. An important feature of the system is that it utilizes a beam displacer to separate the incident laser beam into two orthogonal polarized components propagating in a parallel manner. The beam displacer also acts as a polarization gate for the scattering beams, ensuring the collection of scattering beams maintaining the same polarization state their corresponding incident beams. Verification of our method is done by determining the average size of polystyrene and gold nanoparticles undergoing Brownian motion in liquid suspension, and measuring the transverse velocity of fluid flow through a capillary tube. The average size of Brownian particles are determined by Lorentzian fittings of the measured power spectrums, while the fluid flow velocity is calculated from the amount of spectral shift between the original carrier frequency and the center frequency of the Doppler shifted spectrum. When used as a laser Doppler velocimeter, the proposed system achieves twice the sensitivity as conventional systems. In addition, the localization ability of this laser Doppler and dynamic light scattering system was also demonstrated.

並列關鍵字

dual polarization ； heterodyne ； dynamic light scattering ； laser Doppler ； localization ； Brownian motion

參考文獻

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