cut out the result of this is that the gas jet comes permanently in the same way with respect to the metal and that for a determined adjustment of the pressure of the injected gas the gas jet is always positioned in the same way in relation to the substance treated the shape of the nozzle leads to a clearly supersonic flow at its outlet for a pressure of a few bars the fluid thus enters the cutting out slot slows very suddenly conceeds a great part of its energy and discharges the melted substance by the completely cut out portion of the groove experience shows that the cutting speed increases fairly rapidly when the gas outlet speed rises in the clearly supersonic region for a pressure of 5 bars a speed in the order of a mach 1 7 has been measured at the outlet of the nozzle tube the temperature fo the injected gas is limited in numerous cases by the nature of the frontal lens 2 more particullarly in the case of a beam formed by a light flux whose wavelength is in the order of 10 microns it is obviously difficult to inject a gas at high temperature without ensure effective protection of the frontal lens that protection corresponds to the second variant of the method which in the majority of cases combines with the variant described with reference to the drawings corresponding to fig1 and 2 for a hot gas to act effectively on the substance to be cut out it is an advantage for the gas to have with respect to the temperature of the substance to be melted the greatest difference in temperature possible and.