Effect of population redistribution through Na ∗-Ar and Na ∗-Na ∗ collisions on saturation curves in a vapour cell

• Published in: Journal of quantitative spectroscopy & radiative transfer Vol. 35; no. 1; pp. 1 - 11
• Main Authors: van den Wijngaart, C.A., Kuik, P., Dijkerman, H.A., Hollander, Tj, Krause, L., Alkemade, C.Th.J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1986
• ISSN: 0022-4073; 1879-1352
• DOI: 10.1016/0022-4073(86)90087-7

We report measurements of saturation curves and saturation parameters for Na pumped to the 5S or 4D states by two-photon absorption or broadband radiation from a flash lamp pumped dye laser. The experiments were carried out in a vapour cell with Na densities of 10 12 cm -3 and Ar pressures ranging from 0 to 100 Torr. In general, saturation curves for the laser-excited states were similar to those for lower levels. On the other hand, levels lying above the primarily excited states exhibited abnormal, quadratic saturation curves, which were also observed for the 5S state with 4D excitation and for the 3D state with both 5S and 4D excitation. The normal saturation curves are interpreted on the basis of population redistribution caused by radiative transitions or by inelastic collisions with Ar atoms. The quadratic behaviour is ascribed to energy pooling collisions, an interpretation which is supported by the results of time-resolved fluorescence intensity measurements, showing a secondary fluorescence peak after the termination of the laser pulse. The latter peak could be interpreted on the basis of l-mixing collisions of Na “Rydberg atoms” with Ar. The contribution from ionic channels could be neglected under our experimental conditions.