The University of Southampton
University of Southampton Institutional Repository

Manipulation of particles on optical waveguides

Manipulation of particles on optical waveguides
Manipulation of particles on optical waveguides
A theoretical and experimental study on the optical trapping and propulsion of latex, gold aggregate and colloidal gold particles with average radius of 1.5µm, 250nm and 10nm respectively, in the evanescent region of an illuminated ion-exchange channel waveguide is documented in this thesis.
Optimisation of light-induced forces exerted on a particle on a waveguide relies on two important factors, firstly a maximisation of the intensity and intensity gradient present in the guide-cover interface and secondly, an optimisation of the polarizability of a particle. To this end, a transcendental equation was established and was used to generate design curves for the normalised waveguide thickness required for achieving a maximum gradient force on the guide-cover interface of a waveguide for a specific set of indices.
A study based on Mie theory for the investigation of morphology dependent resonance exhibited by a spherical particle is described. The dependence of resonances on particle radius, index of the sphere with respect to the surrounding medium, absorption, plasmon resonance and symmetry of the incident beam has been investigated. In particular, a simplification of the Mie model was carried out to derive Rayleigh expressions of cross sections from which particle polarizability originates. The validity of the Rayleigh model was assessed with respect to the limiting particle radius.
Based on a semi-classical approach, a derivation of light-induced forces applying to a Rayleigh sphere in the cover region of a waveguide is detailed. The three main optical force components produced are (i) a forward scattering and absorption force due to the intensity of the incident radiation which accounts for propulsion of particles, (ii) a transverse gradient force due to an intensity gradient generated by a decaying evanescent field and finally (iii) a lateral gradient force which arises from the near-Gaussian intensity distribution on a channel waveguide. A comparison of the relative magnitude of each component is described, with additional forces due to gravity, buoyancy and Brownian motion studied.
Factors affecting the propulsion of a gold nanoparticle were investigated. It was shown that the particle velocity is linearly dependent upon the waveguide modal power, increases with a wavelength closer to plasmon resonance in the case of a Rayleigh gold particle, is stronger for TM polarized light, increases with a larger change in the waveguide refractive index and is maximum for a minimum modesize.
For the first time, under the action of light-induced forces generated on the surface of an optical waveguide, colloidal gold particles are propelled in the direction of wave propagation reaching at a maximum velocity of 10µm/s for a modal power of 500mW at lambda=1.047µm. Results obtained will be useful for future applications in particle sorting, fluorescence sensing and surface enhanced Raman sensing of chemical species.
Ng, L.N.
00db8c9f-a390-488e-89a1-9c62f260878c
Ng, L.N.
00db8c9f-a390-488e-89a1-9c62f260878c

Ng, L.N. (2000) Manipulation of particles on optical waveguides. University of Southampton, Department of Electronics and Computer Science, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A theoretical and experimental study on the optical trapping and propulsion of latex, gold aggregate and colloidal gold particles with average radius of 1.5µm, 250nm and 10nm respectively, in the evanescent region of an illuminated ion-exchange channel waveguide is documented in this thesis.
Optimisation of light-induced forces exerted on a particle on a waveguide relies on two important factors, firstly a maximisation of the intensity and intensity gradient present in the guide-cover interface and secondly, an optimisation of the polarizability of a particle. To this end, a transcendental equation was established and was used to generate design curves for the normalised waveguide thickness required for achieving a maximum gradient force on the guide-cover interface of a waveguide for a specific set of indices.
A study based on Mie theory for the investigation of morphology dependent resonance exhibited by a spherical particle is described. The dependence of resonances on particle radius, index of the sphere with respect to the surrounding medium, absorption, plasmon resonance and symmetry of the incident beam has been investigated. In particular, a simplification of the Mie model was carried out to derive Rayleigh expressions of cross sections from which particle polarizability originates. The validity of the Rayleigh model was assessed with respect to the limiting particle radius.
Based on a semi-classical approach, a derivation of light-induced forces applying to a Rayleigh sphere in the cover region of a waveguide is detailed. The three main optical force components produced are (i) a forward scattering and absorption force due to the intensity of the incident radiation which accounts for propulsion of particles, (ii) a transverse gradient force due to an intensity gradient generated by a decaying evanescent field and finally (iii) a lateral gradient force which arises from the near-Gaussian intensity distribution on a channel waveguide. A comparison of the relative magnitude of each component is described, with additional forces due to gravity, buoyancy and Brownian motion studied.
Factors affecting the propulsion of a gold nanoparticle were investigated. It was shown that the particle velocity is linearly dependent upon the waveguide modal power, increases with a wavelength closer to plasmon resonance in the case of a Rayleigh gold particle, is stronger for TM polarized light, increases with a larger change in the waveguide refractive index and is maximum for a minimum modesize.
For the first time, under the action of light-induced forces generated on the surface of an optical waveguide, colloidal gold particles are propelled in the direction of wave propagation reaching at a maximum velocity of 10µm/s for a modal power of 500mW at lambda=1.047µm. Results obtained will be useful for future applications in particle sorting, fluorescence sensing and surface enhanced Raman sensing of chemical species.

Text
Ng_2000_thesis_1460T.pdf - Author's Original
Restricted to Repository staff only
Available under License University of Southampton Thesis Licence.

More information

Published date: 2000
Organisations: University of Southampton, Optoelectronics Research Centre, Electronics & Computer Science

Identifiers

Local EPrints ID: 15499
URI: http://eprints.soton.ac.uk/id/eprint/15499
PURE UUID: 8be4faa9-c728-446d-8791-626bf60fae48

Catalogue record

Date deposited: 09 Jun 2005
Last modified: 26 Jul 2021 16:33

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×