Velocity-modulated drag-trapping of nanoparticles by moving fringe pattern in hollow-core fiber
Abstract
We report optical trapping and transport at atmospheric pressure of nanoparticles in a moving interference pattern in hollow-core photonic crystal fiber. Unlike in previous work at low pressure, when the viscous drag forces are weak and the particles travel at the fringe velocity, competition between trapping and drag forces causes the particle velocity to oscillate as it is momentarily captured and accelerated by each passing fringe, followed by release and deceleration by viscous forces. As a result the average particle velocity is lower than the fringe velocity. An analytical model of the resulting motion shows excellent agreement with experiment. We predict that nanoparticles can be trapped at field nodes if the fringes are rocked to and fro sinusoidally-potentially useful for reducing the exposure of sensitive particles to trapping radiation. The high precision of this new technique makes it of interest for example in characterizing nanoparticles, exploring viscous drag forces in different gases and liquids, and temperature sensing.