Localized Dual-Polarization Differential Heterodyne Dynamic Light Scattering System
Date Issued
2011
Date
2011
Author(s)
Chou, Li-Dek
Abstract
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.
Subjects
dual polarization
heterodyne
dynamic light scattering
laser Doppler
localization
Brownian motion
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-100-R94943160-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):3535a4669bfb6f123bec13a3d8ad1b78