Aerosols are microscopic solid or liquid particles dispersed in a gas. Their study has great significance in fields such as combustion science and atmospheric chemistry. Holding such particles in optical tweezers permits one to measure properties that contribute to the chemical and physical state of the aerosol and hence to its action in the environment, such as nucleation rates, mass and heat transfer, and particle composition, size and mixing state. Optical trapping and manipulation of aerosols poses unique challenges, mainly due to the very low viscosity of the suspending medium, which leads to important inertial effects, but also permits one to explore some new phenomena, such as photophoretic forces, as shown in Fig. 19.1. In this Chapter, we review experiments on both solid and liquid airborne particles, discussing the features that differentiate the manipulation and interrogation of optically trapped aerosols from optical manipulation in a liquid medium.
19.1 Optical tweezers in the gas phase
19.2 Trapping and guiding
19.3 Photophoretic trapping and guiding
19.4 Further reading