Spectroscopic diagnostics of a pulsed discharge in high-pressure argon

Results of investigation of high-pressure argon plasma excited by a high-current pulsed volume discharge are presented. The plasma diagnostics employs spatiotemporal dependences of the emission intensity in the VUV — visible range. A homogenous discharge is observed at pressures up to 10 atm. It is found that the spectrum of the UV — visible photorecombination continuum is sensitive to the discharge constriction. Change in the shape of the spectrum is caused bythe change of the type of positive charge carriers upon passing of the discharge from the uniform phase (molecular Ar₂⁺ ions) to the arc phase (atomic Ar⁺ ions). Experimental data and model calculations show that the electron heating after the main excitation pulse is a highly undesirable process. It slows down the recombination flow in the plasma, which results in stretching of all the kinetic processes for all excited components in time, and hence in a decrease in the peak values of their concentrations. Electron collision-induced mixing effi-ciently converts the reservoir of long-lived Ar₂* molecules in the triplet state into rapidly emitting singlet excimers. It is this mechanism that dominates the production of singlet Ar₂* excimer molecules. The threshold concentration needed to obtain lasing at a wavelength of 127 nm on Ar₂* excimers (¹Σ⁺_u(v=0)) was, according to calculations, about 5×10¹⁵ cm^-3 for the gain 0.05 cm^-1. This concentration can be achieved in the case of homogeneous pulsed discharge pumping with the peak electron concentration 2.×10¹⁶ cm^-3 at the argon pressure 10 atm.