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Issue 47, 2013
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Determining the unique refractive index properties of solid polystyrene aerosol using broadband Mie scattering from optically trapped beads

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Abstract

A method is described to measure the refractive index dispersion with wavelength of optically trapped solid particles in air. Knowledge of the refraction properties of solid particles is critical for the study of aerosol; both in the laboratory and in the atmosphere for climate studies. Single micron-sized polystyrene beads were optically trapped in air using a vertically aligned counter-propagating configuration of focussed laser beams. Each bead was illuminated using white light from a broadband light emitting diode (LED) and elastic scattering within the bead was collected onto a spectrograph. The resulting Mie spectra were analysed to accurately determine polystyrene bead radii to ±0.4 nm and values of the refractive index to ±0.0005 over a wavelength range of 480–700 nm. We demonstrate that optical trapping combined with elastic scattering can be used to both accurately size polystyrene beads suspended in air and determine their wavelength dependent refractive index. The refractive index dispersions are in close agreement with reported values for polystyrene beads in aqueous dispersion. Our results also demonstrate a variation in the refractive index of polystyrene, from bead to bead, in a commercial sample. The measured variation highlights that care must be taken when using polystyrene beads as a calibration aerosol.

Graphical abstract: Determining the unique refractive index properties of solid polystyrene aerosol using broadband Mie scattering from optically trapped beads

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Publication details

The article was received on 16 Aug 2013, accepted on 21 Oct 2013 and first published on 28 Oct 2013


Article type: Paper
DOI: 10.1039/C3CP53498G
Citation: Phys. Chem. Chem. Phys., 2013,15, 20735-20741
  • Open access: Creative Commons BY license
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    Determining the unique refractive index properties of solid polystyrene aerosol using broadband Mie scattering from optically trapped beads

    S. H. Jones, M. D. King and A. D. Ward, Phys. Chem. Chem. Phys., 2013, 15, 20735
    DOI: 10.1039/C3CP53498G

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