EPG ABSTRACT
Mid-infrared CW laser diodes and their application in cavity ring-down spectroscopy
Jerome Remy, Winfred Stoffels, Gerrit Kroesen, Technische Universiteit Eindhoven, Applied Physics Department, den Dolech 2, P.O Box 513, 5600 MB Eindhoven, The Netherlands - EU
Cavity Ring Down Spectroscopy (CRDS) has become a widely used technique for the optical absorption analysis of atoms and molecules because of its great sensitivity and the simplicity of its use. We intend to apply this diagnostic technique to study dust particles in a radio- frequency silane plasma. The wavelength dependant ring-down time is characteristic for the species densities (like SiH4, SiH2, SiH3, SixHy). Hence we can deduce the plasma chemistry during dust formation. We have completed the design of a CRDS experimental set-up, but some optimization is still required. The design is based on 0.1 mW CW multimode lead-salt laser diodes emitting in the mid-infrared wavelength range. An important feature is the spatial structure of the laser beam. Typically, a focused and intense beam is desirable for efficient operation of the CRDS. We will present the results of the IR laser diode beam characterization, using a beam profiler, a Fabry-Perot etalon and a CO-filled reference cell. Preliminary response of the ring-down cavity to IR radiation will be described as well and will show that CRDS in the IR is feasible.
* This work is supported by the European Union as part of the H-Alpha project under contract NNE5-1999-004 and by the Dutch Centrum voor Plasmafysica en Stralingstechnologie
NASA ABSTRACT
Pulsed discharge nozzle optimization and its application to the cavity ring-down spectroscopy of cold PAH ions
J.Remy, TU/e Eindhoven, Applied Physics Dpt, Eindhoven, The Netherlands-EU
L.Biennier, F.Salama & L.J. Allamandola, NASA AMES research center Space Science Division, Moffett Field, USA
J.J. Scherer & A.O'Keefe, Los Gatos Research, Mountain View, USA
An interstellar simulation chamber has been recently developed to measure the absorption electronic spectra of selected free, cold organic molecules/ions. The early phase of this systematic investigation has yielded some substantial results concerning polycylic aromatic hydrocarbon (PAH) ions in an effort to address the problem of the identification of the diffuse interstellar bands*. The experimental set-up design is based on a cavity ring-down (CRD) spectrometer, using a Nd:YAG pumped, UV-visible tunable pulsed dye laser. A pulsed discharge nozzle (PDN) generates the supersonic plasma jets. The PDN assembly allows direct ionization of the carrier gas and its mixture with the gaseous PAH molecules. We will present the most recent advances in the supersonic jet experiments, resulting from the cold plasma source optimization. A better understanding of the electric discharge physics will help us model our laboratory simulation of the diffuse interstellar medium and quantify the mechanism of ion production through Penning ionization.
* L.Biennier, F.Salama, L.J.Allamandola, J.J.Scherer, A.O�Keefe,� Pulsed discharge nozzle cavity ring-down spectroscopy of cold PAH ions�, to be published