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Proceedings Paper

The study of thin films on solid aerosol particles using optical trapping and Mie scattering from a broadband white LED
Author(s): Stephanie H. Jones; Martin D. King; Andrew D. Ward
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Paper Abstract

A counter-propagating optical trap has been used to study thin organic films on the surface of solid particles levitated in air. Micron sized silica spheres have been trapped in air between opposed 1064 nm laser beams, and illuminated with a broadband white LED. Backscattered light from the trapped particle was collected to obtain a Mie spectrum over the 495-670 nm wavelength range and this was used to determine particle radius and wavelength dependent refractive index (Jones et al., 2013). The trapped particle was coated using a flow of organic vapour and the resultant thin film analysed using a coated sphere model. Resonance positions in the Mie spectrum were monitored with time in order to determine film formation, thickness and refractive index. Whilst thin films are believed to form naturally on atmospheric aerosols (Tervahattu et al., 2002), a debate remains as to whether the organic component completely coats the aerosol surface or partially engulfs it. Such films are readily oxidised in the atmosphere causing a change in aerosol properties and knowledge of aerosol properties is required to understand their effect on the climate. The use of optical trapping combined with Mie spectra acquisition to study and characterise coated solid particles is therefore an important step in atmospheric science.

Paper Details

Date Published: 16 September 2014
PDF: 8 pages
Proc. SPIE 9164, Optical Trapping and Optical Micromanipulation XI, 91641X (16 September 2014); doi: 10.1117/12.2061775
Show Author Affiliations
Stephanie H. Jones, Rutherford Appleton Lab. (United Kingdom)
Univ. of London (United Kingdom)
Martin D. King, Univ. of London (United Kingdom)
Andrew D. Ward, Rutherford Appleton Lab. (United Kingdom)

Published in SPIE Proceedings Vol. 9164:
Optical Trapping and Optical Micromanipulation XI
Kishan Dholakia; Gabriel C. Spalding, Editor(s)

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