The position and velocity of optically levitated glass spheres (radii 10–20 &mgr;m) moving in a gas are measured accurately, rapidly, and continuously using a high‐speed rotating polygon mirror. The experimental technique developed here has repeatable position accuracies better than 20 &mgr;m. Each measurement takes less than 1 &mgr;s and can be repeated every 100 &mgr;s. The position of the levitated glass spheres can be manipulated accurately by modulating the laser power with an acoustic optic modulator. The technique provides a fast and accurate method to study general particle dynamics in a fluid.