Four-wave mixing microscopy of nanostructures

The basics of four-wave mixing (FWM) and recent advances in FWM microscopy are reviewed with a particular emphasis on applications in the field of nanomaterials. The vast progress in nanostructure synthesis has triggered a need for advanced analytical tools suitable to interrogate nanostructures one at a time. The single-nanostructure sensitivity of optical microscopy has solidified the optical approach as a reliable technique for examining the electronic structure of materials at the nanoscale. By zooming in on the individual, optical microscopy has permitted detailed investigations of the linear optical response of nanomaterials such as semiconducting quantum dots and plasmon active nanometals. Besides studying the linear optical properties of nanostructures, optical microscopy has also been used to probe the nonlinear optical properties of nanoscale materials. FWM microscopy, a coherent third-order optical imaging technique, has shown great potential as a tool for investigating the nonlinear optical response of nanostructures. FWM microscopy not only permits the characterization of the nonlinear susceptibility of individual nanostructures, it also offers a route to explore the time-resolved dynamics of electronic and vibrational excitations on single structures. In addition, FWM produces strong signals from nanomaterials that are compatible with fast imaging applications, which holds promise for biological imaging studies based on nanoparticle labels that are not prone to photobleaching. © 2011 Optical Society of America