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

Abstract

Nonspherical particles play a key role in the atmosphere by affecting processes such as radiative forcing, photochemistry, new particle formation and phase transitions. In this context, measurements on single particles proved to be very useful for detailed investigations of the properties of the particles studied and of processes affecting them. However, measurements on single nonspherical particles are limited by the difficulties and lack of understanding associated with the optical trapping of such particles. Here, we aim at better understanding the optical trapping of nonspherical particles in air by comparing the motion of an observed nonspherical particle with simulated optical forces and torques. An holographic microscope is used to retrieve the 6D motion of a trapped peanut-shaped particle (3D for translation and 3D for rotation). Optical forces and torques exerted by the optical trap on the peanut-shaped particle are calculated by using FDTD simulations. Most of the main features of the particle motion are in agreement with the calculations while some specific aspects of the particle motion cannot yet be explained.

The physics and applications of strongly coupled plasmas levitated in electrodynamic traps

“…In addition, optical forces and torques exerted by the optical trap on the peanut-shaped particle are calculated using FDTD simulations. A good agreement with the experimental results is obtained for the particle motion, while there are still some specific aspects of the particle motion that cannot be explained [156].…”

“…Such step requires further refining of the experimental setup and a more detailed understanding of the physical processes associated with optical levitation. An investigation of optical trapping of nonspherical particles in air is performed in [156], where an analytical model aimed at better explaining the physical mechanisms is suggested by the authors. The 6D motion of a trapped peanut-shaped particle (3D for translation and 3D for rotation) is analyzed by means of a holographic microscope.…”

“…photochemistry, new particle formation, and phase transitions [156]. The scientific community is highly interested in explaining the physical properties and chemical composition of submicron aerosol particles, in an effort to better characterize radiative forcing [527,529] and air quality [90,417,460,504,508,530].…”

“…Moreover, the Rayleigh limit of charge on a droplet can be investigated using elastic scattering, in order to determine the size and charge corresponding to droplet explosions. Phase function measurements (intensity versus scattering angle) and data gathered from morphology-dependent resonances (MDRs) provide alternative methods to determine the size and refractive index of droplets and microspheres [156,436,549,592], and thus characterize coated spheres [85,593].…”

Characterization and control of droplets optically trapped in air

“…In addition, these experiment can be coupled to obtain a more thorough characterization of single particles. The BLS 15,23 , Raman scattering 15 , photoacoustics 7,20,24 and digital holography 25,26 experiments have already been discussed in details elsewhere and will not be discussed further here. This paper explains the feedback control mechanism and the polarizationresolved TAOS measurements.…”