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

• Published in: Biomedical optics express Vol. 6; no. 10; pp. 4079 - 4087
• Main Authors: Flores-Flores, E, Torres-Hurtado, S A, Páez, R, Ruiz, U, Beltrán-Pérez, G, Neale, S L, Ramirez-San-Juan, J C, Ramos-García, R
• Format: Journal Article
• Language: English
• Published: United States Optical Society of America 01.10.2015
• Subjects: (120.6810) Thermal effects; (350.4855) Optical tweezers or optical manipulation; (140.3300) Laser beam shaping
• ISSN: 2156-7085; 2156-7085
• DOI: 10.1364/boe.6.004079

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.