Low-temperature Bessel beam trap for single submicrometer aerosol particle studies

Abstract

We report on a new instrument for single aerosol particle studies at low temperatures that combines an optical trap consisting of two counter-propagating Bessel beams (CPBBs) and temperature control down to 223 K (-50 °C). The apparatus is capable of capturing and stably trapping individual submicrometer- to micrometer-sized aerosol particles for up to several hours. First results from studies of hexadecane, dodecane, and water aerosols reveal that we can trap and freeze supercooled droplets ranging in size from ~450 nm to 5500 nm (radius). We have conducted homogeneous and heterogeneous freezing experiments, freezing-melting cycles, and evaporation studies. To our knowledge, this is the first reported observation of the freezing process for levitated single submicrometer-sized droplets in air using optical trapping techniques. These results show that a temperature-controlled CPBB trap is an attractive new method for studying phase transitions of individual submicrometer aerosol particles.

Digital holography of optically-trapped aerosol particles

“…The comparison with numerical simulations promises new insight into complex phenomena, such as the coupling of rotational and translational motion in optical traps or the dynamics of optically bound particles. Promising applications in atmospheric sciences include the investigation of the dynamics of phase transitions (freezing 8,10 , efflorescence, and deliquescence 9,64 ) in small aerosol particles which is still not well understood. It has recently become evident that phase transitions in particles are much more complex than previously anticipated and that these processes can happen through multiple, yet unknown pathways 50,[65][66][67][68] .…”

“…A erosol particles undergo many processes that are of great interest for both fundamental and applied research areas. A nonexhaustive list includes optical forces 1,2 , thermophoresis 3 , optical binding [4][5][6] , formation of cloud droplets 7 , phase transitions [8][9][10] , coagulation 11 , evaporation 12 , photochemistry 13,14 , reactions with gases or radicals 13 , ice nucleation 15 , condensation of molecules on particle surfaces 16 , and scattering and absorption of light [17][18][19] . Submicron-sized (both in radius and diameter 20 ) and non-spherical aerosol particles are of particular interest because of their specific properties.…”

Morphology and motion of single optically trapped aerosol particles from digital holography

“…Aerosol particles are of great interest for both fundamental and applied research. They experience many processes including optical trapping 1,2 , optical forces 3,4 , thermophoresis 5 , optical binding [6][7][8] , formation of cloud droplets 9 , ice nucleation 10 , phase transitions [11][12][13] , evaporation 14 , condensation of molecules 15 on their surface, reactions with gases or radicals 16 , photochemistry 16,17 , scattering and absorption of light [18][19][20] . Nonspherical aerosol particles arouse particular interest due to their specific properties.…”

Phase transition dynamics of single optically trapped aqueous potassium carbonate particles

“…We have performed dehydration and hydration experiments on single K 2 CO 3 particles, which were isolated in air with a counter propagating optical tweezer (CPT) inside an environmental cell. Two different types of elastic light scattering, namely two-dimensional angular optical scattering (TAOS) [37][38][39] and broadband light scattering spectroscopy (BLS) [40][41][42] , were used to retrieve information about the particle size, shape (morphology) and refractive index. TAOS measurements are reported in the literature for the study of the phase transitions of micron-sized particles.…”