Trapping and manipulation of microparticles using laser-induced convection currents and photophoresis

E. Flores-Flores, S. A. Torres-Hurtado, R. Páez, U. Ruiz, G. Beltrán-Pérez, S. L. Neale, J. C. Ramirez-San-Juan, and R. Ramos-García

In this work we demonstrate optical trapping and manipulation of microparticles suspended in water due to laser-induced convection currents. Convection currents are generated due to laser light absorption in an hydrogenated amorphous silicon (a:Si-H) thin film. The particles are dragged towards the beam's center by the convection currents (Stokes drag force) allowing trapping with powers as low as 0.8 mW. However, for powers >3 mW trapped particles form a ring around the beam due to two competing forces: Stokes drag and thermo-photophoretic forces. Additionally, we show that dynamic beam shaping can be used to trap and manipulate multiple particles by photophotophoresis without the need of lithographically created resistive heaters.

DOI