Observation of a single-beam gradient-force optical trap for dielectric particles in air

A single-beam gradient-force optical trap for dielectric particles, which relies solely on the radiation pressure force of a TEM00-mode laser light, is demonstrated in air for what is believed to be the first time. It was observed that micrometer-sized glass spheres with a refractive index of n = 1.45 remained trapped in the focus region for more than 30 min, and we could transfer them three dimensionally by moving the beam focus and the microscope stage. A laser power of similar to 40 mW was sufficient to trap a 5-mu m-diameter glass sphere. The present method has several distinct advantages over the conventional optical levitation method. (C) 1997 Optical Society of America.