Aerosol optical chromatography and measurements of light extinction by single particles

Jonathan P. Reid, Bernard J. Mason, Michael I. Cotterell, Thomas C. Preston, Andrew J. Orr-Ewing

Research output: Chapter in Book/Report/Conference proceedingConference Contribution (Conference Proceeding)

4 Citations (Scopus)


To resolve some of the significant uncertainties in the impact of aerosols on global climate, new tools are required to probe light scattering and absorption by aerosol particles. Ideally, such tools should allow direct measurements on individual particles over extended periods of time, providing data to better constrain the optical properties of aerosol, how they depend on the environmental conditions (relative humidity and temperature) and how they change with time. Here, we present a new technique using a combination of a Bessel beam to manipulate individual particles and cavity ringdown spectroscopy for ultrasensitive measurements of the optical extinction. We show that particles can be spatially separated along the propagation direction of a Bessel beam according to their size and refractive index when confined by a Bessel beam core and a counter-propagating gas flow, referred to as optical chromatography. The time-dependent position of a particle is shown to be a consequence of the differing size dependencies of the forces arising from Stokes drag and radiation pressure. We also show that particles captured in a Bessel beam can be moved in and out of an optical cavity formed by two highly reflective mirrors. The time constant for the ringdown in light coupled within the cavity can then be used to measure the optical cross-section of the individual particle with high accuracy. An individual particle can be captured indefinitely and its change in optical cross-section measured with change in environmental conditions.

Original languageEnglish
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherSociety of Photo-Optical Instrumentation Engineers (SPIE)
ISBN (Print)9781628411911
Publication statusPublished - 2014
EventOptical Trapping and Optical Micromanipulation XI - San Diego, United States
Duration: 17 Aug 201421 Aug 2014


ConferenceOptical Trapping and Optical Micromanipulation XI
Country/TerritoryUnited States
CitySan Diego


  • aerosols
  • Bessel beam
  • cavity ringdown spectroscopy
  • light scattering and extinction
  • optical chromatography
  • Optical trapping and manipulation


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