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The concepts of quantum efficiency and ion yield pertinent to a photon detector consisting of an atmospheric pressure oxygen-argon-acetylene (or hydrogen) flame containing magnesium atomic vapour, and also some published experimental results obtained with this detector, are discussed critically. In these experiments, collision-induced ionisation and direct photoionisation of magnesium atoms are performed. In the former instance, one dye laser excites the atoms from the ground state into the 3s3p-1P(1)(0) state and another laser, in temporal and spatial coincidence with the first, brings the excited atoms into the 3s5d-1D(2) state, from which collisional ionisation occurs. In the last instance, direct photoionisation from the 1P(1)(0) level is accomplished either with the excimer laser radiation at 308 nm or by tuning the second laser into an autoionising resonance at 300.9 nm. It is shown that the total loss rate from the 1P(1)(0) level can be calculated by time resolving the resonance fluorescence waveform, with and without the presence of the second laser, and that, by integrating this signal over the duration of the laser pulse, the fluorescence dip obtained can be related to the ion yield of the excitation-ionisation scheme. By evaluating several experimental results obtained with the different laser systems, it is shown that, in the collision-induced ionisation mode, both fluorescence and ionisation measurements are necessary to derive the quantum efficiency, whereas in the direct photoionisation mode, fluorescence data suffice.

Additional information

Authors: OMENETTO N, JRC Ispra (IT);SMITH B W, University of Florida, Department of Chemistry, Gainesville (US);WINEFORDNER J D, University of Florida, Department of Chemistry, Gainesville (US);FARNSWORTH P B, Brigham Young University, Department of Chemistry, Provo (US)
Bibliographic Reference: Article: Journal of Analytical Atomic Spectrometry, Vol. 7 (1992) pp. 89-98
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