Berlin 2005 – scientific programme

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P: Plasmaphysik

P 14: Poster: Niedertemperaturplasmen / Plasmatechnologie 6, Diagnostik 4

P 14.16: Poster

Saturday, March 5, 2005, 14:45–16:45, Poster HU

A Novel Method for Absolute Atomic Density Measurements by Photoionization-Controlled Two-Photon Laser-Induced Fluorescence in Collision-Dominated Media — •K. Niemi, V. Schulz-von der Gathen, and H. F. Döbele — Universität Duisburg-Essen, Fachbereich Physik, Universitätsstr. 5, 45117 Essen

Collisional quenching of excited particles in media at elevated pressure represents the main problem for quantitative fluorescence spectroscopic measurements. We present a novel method based on photoionization-controlled loss spectroscopy [Salmon et al. 1986 Opt. Lett. 11 419] for local measurements of effective quenching rates and, consequently, absolute particle densities with conventional nanosecond laser systems in collision-dominated situations without information on the quenching processes required. For a proof-of-principle we use a flow-tube reactor to generate O-atoms, which are diagnosed in the overlap of two focussed laser beams – one at λ=225 nm for two-photon excitation and the other at λ=338 nm for subsequent photoionization. The particular source provides a basis for comparison, because the quenching rate of the laser-excited atoms can be calculated from measured quenching coefficients and known collider densities. The results of preliminary measurements are promising. The applicability of this method limited by the high radiation intensities required for substantial photoionization and the associated risc of artifical particle generation, e.g. by photodissociation, may be extended using alternative schemes of two-photon excitation to higher states from which photoionization can be achieved with lower photon energies.