Nonlinear Spectroscopy on a Single Quantum System: Two-Photon Absorption of a Single Molecule

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Science  22 Mar 1996:
Vol. 271, Issue 5256, pp. 1703-1705
DOI: 10.1126/science.271.5256.1703


Two-photon fluorescence excitation spectra of single diphenyloctatetraene molecules trapped in an n-tetradecane matrix were measured at cryogenic temperatures. The purely electronic zero-phonon line (transition at 444 nanometers) of these single molecules with a width of about 60 megahertz was excited by a continuous-wave, single-mode laser at 888 nanometers. Even though the two-photon absorption cross section is extremely small, a high photon count rate and low background allowed nonlinear spectroscopy to be extended to the single-molecule level. This experiment also suggests the possibility of two-photon single-molecule scanning microscopy.