VUV-VIS imaging of high-pressure pulsed discharge in argon

Spatial-time behavior of transversally excited pulsed volume discharge in argon is investigated by spontaneous emission spectroscopy and different imaging techniques. VUV Ar-2* emission, UV-VIS continuum and Ar* red lines are used for direct monitoring of discharge homogeneity in the breakdown and recombination stages. Experimental data indicate that Ar* atoms and Ar-2* excimers are created exclusively in the positive column of the discharge, not in near-cathode zones. These zones (cathode sheath and negative glow), however, are the main sources of UV-VIS continuum. The discharge is homogeneous during the first powerful breakdown pulse and fills the whole space between electrodes. Secondary excitation pulses initiate oscillations of plasma emission and longitudinal fragmentation of the discharge into separate zones. Fragmentation is connected with dynamical change of the electron emittance of heated and cold electrodes. Additional electrons, produced during secondary excitation pulses, convert effectively the reservoir of long-lived triplet Ar-2* molecules to fast-emitted singlet Ar-2* excimers - sharp spikes of VUV (126 nm) emission are observed. Double-pulse discharge pumping regime is suggested for easier achievement of the lasing threshold for rare gas excimer lasers.