Laser heating of sulfuric acid droplets held in air by laser Raman tweezers

Oliver R. Hunt, Andrew D. Ward and Martin King
An optical trap is used to hold a droplet of concentrated sulfuric acid in the focus of Ar-ion laser (λ = 514.5 nm). The temperature and concentration of sulfuric acid in the droplet is calculated from the shifts and intensities of the Stokes-shifted Raman bands around 1000rel. cm−1. Aqueous sulfuric acid droplets can thus be used as a ‘thermometer’ for optically trapped droplets in air. It is demonstrated that the laser power can be kept low enough to prevent laser heating of the trapped droplet (necessary for hygrodynamic studies of atmospheric aerosols) and that high laser powers (in excess of 16mW) can result in heating of 5–10◦C.
DOI