The effects of hydrogen additive on the performance and detailed kinetics of a pulsed barium vapour laser operating with burst-mode excitation are reported. Time resolved density measurements of significant atomic and ionic barium states in pure neon buffer gas and in a NeH2 mixture show that the plasma relaxes between excitation pulses much more rapidly when hydrogen is present. The observed improvement in laser performance (65% increase in output pulse energy) under steady state (i.e. end of burst) conditions with hydrogen additive is directly attributable to improved pre-pulse conditions, resulting from cumulative effects of the enhanced plasma relaxation. The results and conclusions are relevant to other cyclic pulsed metal vapour lasers.