Three-dimensional imaging with optical tweezers

We demonstrate a three-dimensional scanning probe microscope in which the e xtremely soft spring of an optical tweezers trap is used. Feedback control of the instrument based on backscattered light levels allows three-dimensio nal imaging of microscopic samples in an aqueous environment. Preliminary r esults with a 2-mu m-diameter spherical probe indicate that features of app roximately 200 nm can be resolved, with a sensitivity of 5 nm in the height measurement. The theoretical resolution is limited by the probe dimensions . (C) 1999 Optical Society of America.