Optical Trapping and Two-Photon Exitations of Quantum Dots

Abstract

Individual colloidal quantum dots can be optically trapped and manipulated by a single infrared laserbeam operated a low laser powers [Jauffred et al. Nano letters 2008 (10)] and the spring constant of the force, exerted by the harmonic optical trap on a quantum dot, have been found to be of the order of 10−4 pN/nm. We measured the optical trapping strength of individual colloidal quantum dots with different emission wavelenghts (from 525 nm to 800 nm) and different physical sizes, with the result that these diverse quantum dots have identical trapping capabilities. Furthermore, we show that the trapping laserlight can also act as a source for two-photon excitation of the trapped quantum dots, thus eliminating the demand for an excitation light source in addition to the trapping laser beam.