Optical Trapping Single Dust Particles in Plasma For In Situ Plasma Diagnostics.*

Optical trapping (OT), conventionally called optical tweezers, use photon radiation pressure force and or photophoretic force to levitate, trap, or transport micron-sized particles (solids or droplets) in different media including air, solution, and reactive gaseous. Very recently, this technology has been demonstrated in plasmas, which shows great promise of a new tool using a single dust particle for in situ noninvasive plasma diagnostics, with high spatial resolution. Here we present our recent developments in OT of various types of particles (size, morphology, and material) in rf plasma and weakly magnetized rf plasma. We show a trapped particle can be smoothly transported in the plasmas vertically along the gravitational field or horizontally perpendicular to the electric field. We use a single trapped particle to measure the electric field in the plasma, operating in various situations. We discuss further potentials for in situ, noninvasive, plasma diagnostics at the microscopic level using a micron-sized particle.