Interference effects in laser heating of metals in an oxidizing medium

An investigation is made of the kinetics of laser heating of metal targets in air. It is shown that when the wavelength is shortened (in particular, from 10.6 $\mu m$ to 1.06 $\mu m$ or shorter), the character of the heating changes substantially. Firstly, the number of fluctuations of the absorptivity of the target increases and, secondly, the “high-frequency” fluctuations are modulated by “low-frequency” fluctuations. It is shown that this behavior of the absorptivity is due to the formation of several oxide films with different oxygen contents on the surface of the target. Using a copper target as an example, a detailed analysis is made of the behavior of various quantities characterizing the heating (such as the thickness of the oxide films, temperature, and growth rate of the oxide films). The experiments show good agreement with the theory.