Energy transfer and optical gain studies of FDS: RhB dye mixture investigated under cw laser excitation

Radiative and non-radiative (Forster type) energy transfer processes in a dye mixture of FDS and Rh B in methanol under cw Ar ion laser excitation were investigated for fixed donor concentration and varying acceptor concentration. It is found that most of the pump power absorbed by FDS is transferred to Rh B as a useful pump power. Transfer probability (P-DA), transfer efficiency both radiative (eta (R)) and non-radiative (eta (NR)) and optical gain (G) of the system were studied for various pump powers. The gain characteristics of Rh B are found to alter due to the change in the effective fluorescence lifetime caused by energy transfer reaction. Theoretical calculations were also done to find the total transfer efficiency (eta (T)) at various acceptor concentrations to identify the appropriate energy transfer mechanism responsible for gain enhancement in Rh B. Both radiative and non-radiative transfer processes are taken into consideration in all the calculations. Various energy transfer parameters viz. radiative rate constant (K-R), non-radiative rate constant (K-NR), critical concentration (C-0), critical radius (R-0) and half quenching concentration ([A](1/2)) are calculated by using the Stern-Volmer plots and concentration dependence of radiative and non-radiative transfer efficiencies. Concentration and pump power dependence of the peak gain and lasing wavelengths of the energy transfer dye lasers (ETDL) have also been studied. The experimental results show that the dominant mechanism responsible for the efficient excitation transfer in this mixture is of radiative nature, whereas the long range dipole-dipole (d-d) interaction (Forster type) is comparatively smaller. (C) 2001 Published by Elsevier Science B.V.