Tunable dye laser spectroscopy of atomic calcium: collisional redistribution of radiation

By tuning a pulsed dye laser through the resonance line of calcium at 422.7 nm the authors have investigated the spectral redistribution of laser radiation by calcium vapour. Two main components were resolved in the side emission from an oven containing calcium vapour and argon buffer gas. These are produced by Rayleigh scattering and by collision-induced fluorescence. The intensity of the Rayleigh component was found to vary as Delta -2 where Delta = omega 21 - omega L is the laser detuning from resonance. In contrast the intensity of the collision-induced fluorescence showed a markedly asymmetric dependence on detuning. Detailed studies of the collision-induced fluorescence have enabled the complete line shape of the calcium resonance line perturbed by argon to be determined. The interpretation of this data in terms of a frequency-dependent collision rate, gamma E ( Delta ), is discussed. This paper also reports calculations of theoretical line profiles using the unified Franck-Condon theory and trial interatomic difference potentials. The comparison of the experimental and theoretical line profiles enables the range of validity of the unified Franck-Condon theory to be assessed and the form of the optimum Ca-Ar difference potential to be selected.