Optical force of a TEM00 light beam on a sphere with refractive index less than its surrounding medium

The force acting on a micro-sphere with refractive index less than its surrounding medium by a TEM00 mode focused light beam is investigated both theoretically and experimentally. It is demonstrated that although the force is mainly a repulsing one, optical trapping is available in the cases in which the sphere is closed to the beam axis of the light and located closely before its focus. By moving an aqueous micron sphere in an oil medium, then fusing it into a larger aqueous sphere encapsulating microbes and acting as a micron-bioreactor, we demonstrated the force and its potential applications.