Study of laser behaviour in C-440 and C-485 dye mixture

Abstract

The laser behaviour in the C-440 (donor) and C-485 (acceptor) dye mixture in ethanol is studied and discussed by investigating the gain characteristics at various acceptor concentrations (1 X 10 -4 M/L to 1 X 10 -2 M/L) and pump powers of the N 2- laser. It is found that most of the pump power absorbed by C-440 is transferred to C-485 as a useful pump power. The gain characteristics of C-485 are found changed due to the change in the effective fluorescence lifetime caused by the energy transfer reaction. The theoretical calculations were also done to find the total transfer efficiency at various acceptor concentrations to identify the appropriate energy transfer mechanism responsible for gain enhancement in C-485. These calculations take into account the contributions due to both radiative and nonradiative energy transfer. The energy transfer rate constants and critical transfer radius ( R 0) are calculated by using Stern-Volmer plots and concentration dependence of radiative and nonradiative transfer efficiencies. The concentration dependence of laser peak gain and the lasing wavelengths of the ETDL have also been studied. The experimental results indicate that the dominant mechanism responsible for the efficient excitation transfer in this mixture is of nonradiative nature due to long range dipole-dipole interaction. It is also found that the TICT state formation possibility in excited states is either reduced for the acceptor dye in the presence of donor or these TICT states become nonradiative.