Specific behaviors of dynamic optogalvanic signals of an argon hollow cathode discharge

Dynamic optogalvanic signals for Ar metastable transition in a hollow-urani um cathode discharge have been measured by pulsed diode laser irradiation a t 772.376 nm (1s(5)-2p(7) transition in Paschen notation). Oscillations and Penning ionization-related behaviors in the dynamic optogalvanic signals h ave been reported. Based on the simultaneous observations of the oscillatin g features in both the density of metastable atoms and emission intensities of the 1s-2p transitions, one of the possible mechanisms for the voltage o scillation is considered to be related to the stepwise ionization of the me tastable atoms due to collisions with Slow electrons in the discharge. We s how by Fourier transform analysis that the oscillation is composed of two d ifferent frequencies, one at about 9 kHz and the other at about 29 kHz. Eac h frequency is interpreted as the diffusion and the stepwise ionization rat e of the metastable atoms, respectively. The Penning ionization-related sig nals, which show the extra component at the time of about 150 mu s, are cha racterized only in a distinctive negative slope region in the voltage-curre nt curve of the discharge. (C) 1999 Elsevier Science B.V. All rights reserv ed.