T. Plakhotnik et al., NONLINEAR SPECTROSCOPY ON A SINGLE QUANTUM SYSTEM - 2-PHOTON ABSORPTION OF A SINGLE-MOLECULE, Science, 271(5256), 1996, pp. 1703-1705
Two-photon fluorescence excitation spectra of single diphenyloctatetra
ene molecules trapped in an n-tetradecane matrix were measured at cryo
genic 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 ext
remely small, a high photon count rate and low background allowed nonl
inear spectroscopy to be extended to the single-molecule level. This e
xperiment also suggests the possibility of two-photon single-molecule
scanning microscopy.