The chopping method, i.e. a dynamic method, was applied for the determination of the effective absorptivity of a vanadium metal-vanadium oxide system during CW CO 2 laser oxidation in atmospheric conditions. The earlier procedure used long-time continuous heating and cooling. The absorptivity values measured by both methods are compared. The maximum deviation between results for the earlier and the new method was found to be as large as 30%. One of the main advantages of the new dynamic method is that the time dependence of absorptivity can also be calculated. Calculations show that, at constant temperature, the absorptivity decreases with time. This effect can be explained by taking into account the heat capacity of the grown oxide layer, and allows us to estimate the mass of the oxide as a function of time.