Optical micromanipulation of aerosols

Abstract

This thesis describes my work on the development of optical trapping techniques for manipulating airborne particles. Although many of the basic principles are similar to those used in more conventional colloidal experiments, there are many differences which have been described and investigated in detail in this work. Basic characterisation measurements are made, such as axial Q and sample size selectivity, for a number of sample liquids in a basic optical tweezers setup. Performance at 532nm and 1064nm were compared and shown to be very similar, despite increased absorption in the infrared. A successful method was developed for the optical trapping of solid aerosol particles, allowing a direct comparison between similar particles suspended in both the gas and liquid phase. A single beam levitation trap was developed for transporting liquid aerosols to allow multiple chemical measurements to be made on a single droplet. Performance between Gaussian and Bessel beams was compared for various liquids, with guiding distances of several millimetres being achieved with the Bessel beam geometry. An experiment to demonstrate lasing within an optically tweezed droplet was also performed and spectra were taken. Although strong resonance modes were evident, the data was not conclusive. However, it is likely that a redesign of the experiment would be successful. These techniques have extended research capabilities in the areas of both optical trapping and atmospheric chemistry, allowing the detailed study of single aerosol particles in the 1-10 μm range.