Quantifying Forces on Strongly Absorbing Materials Rotating in Optical Traps
Optical trapping or “tweezing” is a laser-based method of micron-scale material manipulation, exploiting the forces produced by light refracting through small particles to capture them within a particular area (the trap). Biologists and chemists use this technology to handle large molecules, mix small volumes of liquids, and even build cell-scale machinery. In this research project, we use Laguerre-Gauss modes to create the trap and rotate the particles. Generating the Laguerre-Gauss modes is achieved through programming a spatial light modulator (SLM) with a holographic phase pattern. We work with several different combinations of particles (polystyrene latex, silica, mica, graphite, and vermiculite) and solutions (deionized water, SDS) to conduct experimental tests of the effective trapping and rotation of strongly absorbing materials. When a particle is sufficiently trapped, we apply an alternating current to a piezoelectric to oscillate the solution and quantify the trapping force that is present. We also perform theoretical calculations of trapping forces in laser modes carrying orbital angular momentum (OAM). Here, we present the results of our measurements and calculations and show the forces acting on the particles.