Noise amplitude spectra for direct-current plasma atomic emission spectrometry (DCP-AES) were acquired. Flicker (1/<i>f</i>) noise dominates the signal at low frequencies, and white noise prevails at higher frequencies. Broad-band audio-frequency (af) noise was observed in the plasma continuum emission when the nebulizer gas was directed into the discharge. By increasing the electrode-gas flows, it was possible to narrow the frequency range and increase the amplitude of this af noise. The introduction of an easily ionized element into the plasma had little effect on the noise characteristics of the source.
Curtis A. Monnig and Gary M. Hieftje, "An Investigation of Noise Amplitude Spectra Produced by a Direct-Current Plasma," Appl. Spectrosc. 43, 742-746 (1989)