The expansion dynamics of Ga and GaN laser-ablation plumes were studied in vacuo using time-resolved extreme ultraviolet absorption spectroscopy. Targets of either Ga metal or pressed and sintered GaN pellets and a Nd-YAG laser (1.06 mum) at a fluence of 10 J cm(-2) were used. Spatio-temporal maps of the relative concentration of Ga+ an constructed by measuring the transmission through the ablation plumes of a pulsed beam of ultraviolet radiation tuned to 3p --> 3d inner-shell transitions in Ga+. Marked differences between the Ga and GaN plumes were observed. The results are discussed in the context of the growth of GaN by Pulsed Laser Deposition (PLD).