Selection and characterization of aerosol particle size using a bessel beam optical trap for single particle analysis

Abstract

Bessel beams were used to create a counter-propagating optical trap for capturing and manipulating aerosol particles. Aerosol droplets were characterized through measurement of the elastic scattered light at three wavelengths; the trapping wavelength of 532 nm was used in conjunction with two probe beams at 405 nm and 633 nm to reduce the uncertainty in estimating droplet radii of 1 μm or less. Control of the aerosol size distribution sampled by the counter-propagating trap was demonstrated by varying the trapping beam core diameters and intensities. Smaller droplet sizes were preferentially selected with a 1.7 μm core diameter compared to cores of 2.7 μm and 4.5 μm. Further, an increase in core intensity was shown to broaden the range in droplet sizes that were optically trapped. The possibility of using such an approach to isolate and analyze the properties of single accumulation mode aerosol particles is discussed.

Deviations from Plane-Wave Mie Scattering and Precise Retrieval of Refractive Index for a Single Spherical Particle in an Optical Cavity

“…The particle radius was obtained from the analysis of interference fringes for light scattered from the trapping laser and collected over a known angular range (the phase function). [11][12][13] In the analysis described in section 5, the beam waist of the TEM00 mode was obtained as 279 m, which compares well to the value expected for our design of linear optical cavity of 272 m. 9 Experimental measurements are overlaid by Mie scattering calculations in (2) to account for the measurement of extinction by light scattering within an optical cavity.…”

A complete parameterisation of the relative humidity and wavelength dependence of the refractive index of hygroscopic inorganic aerosol particles

“…1 in Cotterell et al (2015a) and Fig. 4 in Carruthers et al (2012) for examples of raw PF images recorded using our instrumentation. As described previously (Cotterell et al, 2015a, b), a mean Pearson correlation coefficient c (n λ ) is used to quantify the level of agreement between the measured PF data set and the set of best-fit Mie theory simulations, with c (n λ ) = 1 corresponding to perfect agreement and lower values of c (n λ ) indicative of a poorer fit.…”

Angular scattering of light by a homogeneous spherical particle in a zeroth-order Bessel beam and its relationship to plane wave scattering

“…[18][19][20][21][22] In the field of aerosol science, Bessel beams are very appealing for the study of single aerosol particles and instrumentation 2 incorporating such beams has been recently demonstrated. [23][24][25][26][27][28][29] However, there remains the need for an approach to accurately characterize a particle once it has been trapped in such a beam. For a homogeneous spherical particle the radius and refractive index must be accurately determined.…”