ONE-PHOTON AND 2-PHOTON SPECTROSCOPY ON SINGLE MOLECULES OF DIPHENYLOCTATETRAENE

We report investigations on one- and two-photon excitation of single m olecules of diphenyloctatetraene in n-tetradecane at cryogenic tempera tures. Saturation intensities, count rates and linewidths of single mo lecules are compared with corresponding ensemble values obtained from statistical fine structure investigations. The single-molecule linewid ths under one-photon excitation are generally two to three times narro wer than in two-photon excitation spectra. This effect is discussed wi th respect to saturated spectral diffusion induced by the high power I R light necessary for efficient two-photon absorption.