Measurements of negative-ion densities by cavity ringdown spectroscopy
Institut für Laser- und Plasmaphysik, Universität GH Essen - D-45117 Essen, Germany
Accepted: 30 October 1998
We report in this letter the first application of Cavity Ringdown Spectroscopy (CRDS) to the quantitative detection of negative ions —-ions in a magnetic multipole source in this specific case. The absorption connected with the photodetachment process is measured. A pulsed () green () laser (Nd:YAG with SHG) beam is radiated into a high-Q cavity containing the discharge plasma. The temporal behaviour of the decaying pulse at the cavity exit yields the density of absorbing -ions on the basis of the known (broadband) photodetachment cross-section. The densities determined by CRDS agree well with earlier measurements obtained with a multipass scheme and with the alternative method which consists in the detection with a Langmuir probe of the electrons released in the photodetachment process.
PACS: 52.70.-m – Plasma diagnostic techniques and instrumentation / 52.70.Kz – Optical (ultraviolet, visible, infrared) measurements / 52.25.Rv – Emission, absorption, and scattering of visible and infrared radiation
© EDP Sciences, 1999