Controlled aerosol manipulation using holographic optical tweezers

We demonstrate the use of holographic optical tweezers for the optical trapping and manipulation of arrays of airborne water droplets (aerosols). Making use of a phase-only spatial light modulator we present evidence of stable, interactive manipulation of both single and multiple aerosol droplets, of the order of 10 microns in diameter, and also their controlled coagulation. We discuss the advantages, disadvantages, and limitations of using a spatial light modulator for droplet manipulation including the implications of the update speed of the device (a Holoeye LC-R2500 SLM), diffraction efficiency, and droplet growth and evaporation due to laser intensity variations. We will examine the generic difficulties of trapping in air, working in the absence of inertial damping. Finally we will discuss the applications of the above work in fields such as atmospheric chemistry and microfluidic microchemical reactors whilst presenting preliminary results on fusion of two or more droplets of differing phases.