Estimation of molecular parameters in laser grade dyes: Coumarin 450 and Coumarin 460

Optical gain spectroscopy is exploited to examine photo-physical parameters viz. absorption and emission cross-sections, threshold pump rate, excited to ground state rate constant in two important molecules of Coumarin class of laser grade dyes. The results for the intensity dependent gain coefficient for ethanolic solutions of Coumarin 450 (C-450) and Coumarin 460 (C-460) have been presented in the concentration range from ∼1 × 10−5 to ∼1 × 10−2 mol/l under nitrogen laser excitation. The concentration dependent threshold pump rate, small signal gain coefficient and saturation parameter have also been investigated. The results have been explained in terms of variation of fluorescence lifetime with concentration that originates due to excited state absorption.