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- (3-sulfopropyl)-5,5',6,6'-tetrachlorobenzimidazolocarbocyanine (also known as BIC) adsorbed onto colloidal silver was examined as a function of laser pulse energy at room temperature. BIC is found to aggregate on colloidal silver, and the number of coherently responding molecules involved in the one-exciton state (i. e., the coherence length) was estimated to involve 8-9 molecules. Lasing at a remarkably low incident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in coherently coupled adsorbed molecules that emit photons which stimulate emission from other spatially distributed superradiant states. (C) 1998 American Institute of Physics. [S0003-6951(98)03140-4].