Nonlinear line narrowing of excited state resonances in perylene doped poly(methylmethacrylate) using multiply enhanced nonparametric spectroscopy

Abstract

Line narrowing of perylene vibronic transitions in poly(methylmethacrylate) (PMMA) samples has been demonstrated using multiply enhanced nonparametric spectroscopy. Three lasers are used to generate a four wave mixing signal that is resonantly enhanced by three simultaneous perylene resonances involving a vibrational state, a vibrationless excited electronic state, and a vibronic state of the excited electronic state. There is a correlation between the position of the electronic and vibronic states within the inhomogeneously broadened absorption spectrum. The correlation can be used to achieve line narrowing by fixing one of the resonances to a subset of perylene sites within the inhomogeneous profile so the other resonance of those sites will be selectively enhanced. The position of the line narrowed vibronic peaks depends upon the electronic detuning from the center of the inhomogeneously broadened absorption band as different sites within the band are probed. Excited state coherent processes involving resonance with higher singlet states are shown to be unimportant from the detuning dependence on a simultaneous vibrational enhancement.