Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE
Optical Bistability In Dimer-Monomer Dye Systems
Shammai Speiser, Frank L. Chisena
Abstract
Optical bistability has been observed in highly concentrated fluorescein dye solutions and in thin (-1 pm) doped polymeric films. At concentrations larger than 10-5 mole/k dye dimers are formed. For fluorescein dye, the dimer-monomer equilibrium constant is 10 -5 mole/ℓ so that most of the dye species are in the dimer form. At 480 nm the dimer absorption cross section is 10-18 cm2/molecule, while that for the dye monomer molecule is 7.6 x 10-17 cm2/molecule. Upon laser excitation dimers dissociate to form monomers thus providing a highly nonlinear laser induced absorption. This high nonlinear absorption coefficient can be utilized for optically bistable response of the dye system. Optical bistability was observed by placing dye solutions or dye thin films inside a Fabry-Perot resonator and exciting it with 480 nm dye laser pulses of 10 ns duration. The effect is more pronounced in 10-4 mole/ℓ fluorescein than in 10-6 mole/k fluorescein in which dimer formation is not that efficient.