Optical and Plasmon based Trapping : Towards Structured Light Fields

Abstract

We have studied various aspects of development as well as applications of Optical traps. Design considerations of single beam optical traps and holographic optical traps using computer-controlled spatial light modulators(SLM) have been discussed and dealt with in this work. We predominantly use a 633nm He-Ne laser to trap 3-5 μm silica beads in various configurations. An introduction to structured light fields and in-depth studies of creation and properties of Bessel beams has been done. An SLM can be used to project holograms on its display which can alter both the amplitude and phase of incident light. This results into tailored light fields of different kinds. We have also demonstrated plasmonic trapping based on localized surface plasmons on a gold film coated glass slide. The evanescent mode of a 1064nm laser couples effectively at SPP resonance angle due to total internal reflection geometry of a dove prism. This leads to excitation of surface plasmon polaritons(SPP) on the gold film and formation of aggregates of 3μm silica beads which get trapped in this plasmonic potential well. Mobility of such aggregates with the movement of the incident laser spot has also been shown. Further, plans of using structured light fields(e.g. Bessel beams) in such experiments are discussed.