Flow Investigations of Pulsed Arc Discharge Recombination Lasers

Abstract

Metal vapor recombination lasers of the SPER-type (Segmented Plasma Excitation and Recombination) were first developed and operated by SILFVAST et al. /1–3/. The laser active species is produced and the laser mechanism initiated in pulsed arc discharges over stall electrode gaps. The ends of short wire pieces that are aligned parallel to the optical axis of the laser resonator serve as the electrodes. Some electrode metal is vaporized and ionized in the arc discharges. A spherical cloud of plasma expands rapidly from each gap into a background gas. Cooling by the adiabatic expansion and by collisions with the background gas at the plasma front causes a rapid recombination of the ions. Within the recombination relaxation time the upper electronic levels are populated preferentially by collisions with electrons and inversions may develop. WÄGLI and BOHN /4/ have presented a theoretical model for this laser, based on the similarity theory of SEDOV for the strong explosion in a homogeneous atmosphere /5/. The rapid build-up of the plasma and its subsequent expansion creates a strong shock wave (Fig. 1), and at the contact front of the plasma with the shocked gas develops a diffusion zone with enhanced collisional cooling of the electrons and large electron heat transfer.