[en] A theoretical analysis of the gas dynamics of the Mach-disk technique in laser evaporation experiments is presented. The relation between stagnation pressure, sonic pressure, and saturation pressure is given, and the equivalent sonic orifice diameter for laser-induced vaporization is calculated. Experimental results on UO₂, which make use of the results of this analysis, are presented. These measurements, in the temperature range 3700-4200 K, confirm previous data for the total vapour pressure. The vaporization mechanism at extreme rates of evaporation and the relevance of equilibrium calculations to high-temperature evaporating systems are also discussed. (author)