SUPERRADIANT LASING FROM J-AGGREGATED MOLECULES ADSORBED ONTO COLLOIDAL SILVER

The picosecond time-resolved emission spectrum of the cyanine dye 1,1' -diethyl-3,3'-bis- yl)-5,5',6,6'-tetrachlorobenzimidazolocarbocyanine (also known as BIC) adsorbed onto colloidal silver was examined as a f unction of laser pulse energy at room temperature. BIC is found to agg regate on colloidal silver, and the number of coherently responding mo lecules involved in the one-exciton state (i. e., the coherence length ) was estimated to involve 8-9 molecules. Lasing at a remarkably low i ncident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in cohe rently coupled adsorbed molecules that emit photons which stimulate em ission from other spatially distributed superradiant states. (C) 1998 American Institute of Physics. [S0003-6951(98)03140-4].