Optically induced rotation of a trapped micro-object about an axis perpendicular to the laser beam axis

A strongly focused Nd:YAG laser beam has been used experimentally to achieve optical trapping and simultaneous rotation of a micro-object about an axis perpendicular to the trapping laser beam axis. The micro-object (12 μm in diameter), which has shape anisotropy in its interior, can be produced by oxygen reactive ion etching of a fluorinated polyimide film (refractive index n=1.53). This optically induced rotation of the micro-object in ethanol (n=1.36) is accomplished by utilizing the net radiation pressure force arising from the momentum change of light scattered at the micro-object's inner walls.