A single-beam gradient-force optical trap for dielectric particles, wh
ich relies solely on the radiation pressure force of a TEM00-mode lase
r light, is demonstrated in air for what is believed to be the first t
ime. It was observed that micrometer-sized glass spheres with a refrac
tive index of n = 1.45 remained trapped in the focus region for more t
han 30 min, and we could transfer them three dimensionally by moving t
he 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.