Technique for distinguishing and determining the origin of photon emissions from complex plasmas
. Rev Sci Instrum 2002
A technique has been developed to separately obtain emission spectra from individual ion-molecule and electron-ion recombination reactions. This involves using a flowing afterglow to create the reaction producing the emissions of interest and pulse modulating a gas into the afterglow that reacts with only the ion species causing that reaction in the plasma. In this way, photon emissions have been detected where other interfering emissions from the ionization source and from other reaction processes, are more than an order of magnitude larger. The technique has been tested with an He+/Ar+ plasma to which OCS had been added. In this case, with pulsed modulation of H-2 into the plasma, emissions can be isolated from Ar+ reactions and from the electron recombination of its ion products, as well as from similar reactions involving H-3(+) (generated from the Ar+ reaction with H-2). The technique is such that the majority of the data acquisition time is devoted to collecting data where there is significant signal with little time being used in wavelength regions where there is no significant signal. In these scans, photon counting times are varied to give all signal peaks the same signal to noise ratio independent of intensity and thus the same statistical significance. This is a considerable improvement over standard spectral scanning approaches. Critical features of the technique are evaluated and the means of optimizing the scan are discussed. (C) 2002 American Institute of Physics.