Optical tweezers: Manipulation of matter with light

A review of our research activities on optical manipulation of microparticles will be presented. In particular we will describe a theoretical and experimental analysis of an interferometric optical trapping device that allows efficient sorting of particles, including biological samples, either by size or refractive index. This technique involves no microfluidic flow. It is based on the specific response of different microparticles to a phase-modulated interference pattern. The effect of the light absorption of the fluid in optical tweezers, which is usually considered as an undesired side effect, will be discussed. We will show that heating due to absorption can induce microflows which can be used to efficiently collect DNA molecules. Even more, if the absorption is too large, then cavitation can be generated with cw radiation opening a new research field of the so called sonochemistry.