Saturation of molecular impurity vibronic transitions under strong laser excitation

The saturation of inhomogeneously broadened vibronic S(1)-S(0) transitions has been investigated experimentally in the perylene impurities of anthracene single crystals under pulse dye laser excitation at 4 K. Methods are developed for determining the homogeneous widths and vibronic dipole transition moments of perylene, on the basis of the experimental results. A vibrational relaxation time of 55 ps was calculated for a vibronic mode of 358 per cm in the excited S(1) state. The dipole transition moment for the vibronic no-phonon fluorescence line in perylene was 0.03 D. An upper limit of 10 to the 3rd to 10 to the 4th W/sq cm was estimated for the nondistortional excitation power of the vibronic transitions and phonon sidebands in perylene, and an upper limit of 10 W/sq cm was estimated for the 0-0 transitions.